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I'm using a Haynes Maintenance manual:
1. Check your fuses there are a total of 5 fuses and 1 fusible link (so let's concentrate on the a/c compressor circuits)Your blower motor works? Your a/c controller is power? Ok great there are 2 fuses that control the compressor clutch.
2. Remove the A/c relay& Check power at the relay Pnk/Blk wire (trigger circuit) there should be 12 volts (smaller gauge wires) only in start or run.
3. The Blk/Red is the ground side that goes back to the ecu. (smaller gauge wires) turn the switch on and check that there's a ground here w/o the relay installed.
4. Check power at the green wire (large gauge) this is the load power source. 12 volts at all times.
5. The Yel/Blk wire is the Load component side of the load circuit. Check for continuity from here to the compressor clutch wire!
Complete these test and see what you find....
Really sounds like a faulty pressure switch or pressure switch circuit or Maybe debris inside the pressure switch so it doesn't really know whats going on....try a junkyard a/c controller if you don't have one maybe I can ship one to you! I hope you have access to an a/c recovery system!
I had an aircraft that the air crew complained about the aircraft being to Hot all the time. The assigned mechanic was a parts changing SOB. He kept changing compressors, relays, etc....I went to that base troubleshot it to the Pressure switch. Bypassed the pressure switch and the a/c run fine we changed the faulty pressure switch and hooked everything back up and the a/c didn't work! So I figured the pressure wasn't getting to the pressure switch. Depleted the entire system took the schrader valve out that the pressure switch screws into and come and behold some debris was clogging up the system side of the schrader valve & it looked like teflon tape. I removed and cleaned the schrader valve, reinstalled the schrader valve, pressure switch, and reserviced the aircraft a/c system ground ran it and it worked like a champ...Now the Air crew complained it was too cold!
Let me know if you can try another a/c controller you might have on hand....GL
Really sounds like a faulty pressure switch or pressure switch circuit or Maybe debris inside the pressure switch so it doesn't really know whats going on....try a junkyard a/c controller if you don't have one maybe I can ship one to you! I hope you have access to an a/c recovery system!
....
Let me know if you can try another a/c controller you might have on hand....GL
Hi CMax, thanks a lot for your help. Regarding the a/c controller, I'm not exactly sure what you're referring to, but I am sure that I don't have a spare on hand. By A/C controller do you mean the dash control? I went through all your checks, so let me try to respond to those:
1) Yes, my blower motor works, and the A/C controls light up and are responsive. Per the FSM, I did check the two 7.5A fuses, and those were fine. Perhaps those are the 2 fuses you're referring to, and in the diagram I attached? You may recall from my first post that I did initially find a blown 7.5a fuse in the dash after replacing the compressor. I'm not sure when that fuse blew (I guess it could have occurrred when the original compressor locked up?), but I replaced it and it has not blown again since.
2) Check!
3) This read ~14.2V regardless of switch on or off.
4) Check!
5) Check!
Regarding the pressure switch, I can't say for sure if that's working yet or not, but what I know is that the input to that switch (pin 4 on the switch connector) is not toggling on and off with the A/C control switch. It remains at ~0V regardless of A/C on or off. So even if the switch is working properly (and I have no reason to believe it's not right now), the input to the ECU control (pin 21) is never telling the ECU to set pin 12 to ground (which goes to the A/C relay input trigger, or pin 2 of the A/C relay).
From what I can decipher from the FSM, pin 4 on the triple switch connector should come from pin 5 of the A/C auto amp., so I'm assuming the problem is either the A/C auto amp itself, or some wiring in between. I suppose the A/C auto amp is part of the a/c controller you're talking about? What's the procedure for swapping that out?
Hi CMax, thanks a lot for your help. Regarding the a/c controller, I'm not exactly sure what you're referring to, but I am sure that I don't have a spare on hand. By A/C controller do you mean the dash control? I went through all your checks, so let me try to respond to those:
1) Yes, my blower motor works, and the A/C controls light up and are responsive. Per the FSM, I did check the two 7.5A fuses, and those were fine. Perhaps those are the 2 fuses you're referring to, and in the diagram I attached? You may recall from my first post that I did initially find a blown 7.5a fuse in the dash after replacing the compressor. I'm not sure when that fuse blew (I guess it could have occurrred when the original compressor locked up?), but I replaced it and it has not blown again since.
2) Check!
3) This read ~14.2V regardless of switch on or off.
4) Check!
5) Check!
Regarding the pressure switch, I can't say for sure if that's working yet or not, but what I know is that the input to that switch (pin 4 on the switch connector) is not toggling on and off with the A/C control switch. It remains at ~0V regardless of A/C on or off. So even if the switch is working properly (and I have no reason to believe it's not right now), the input to the ECU control (pin 21) is never telling the ECU to set pin 12 to ground (which goes to the A/C relay input trigger, or pin 2 of the A/C relay).
From what I can decipher from the FSM, pin 4 on the triple switch connector should come from pin 5 of the A/C auto amp., so I'm assuming the problem is either the A/C auto amp itself, or some wiring in between. I suppose the A/C auto amp is part of the a/c controller you're talking about? What's the procedure for swapping that out?
Apparently you and I aren't on the same page! Let's try it again: Scenario again is with the a/c relay removed!
1. Checking the 2 fuses.....You said you checked> Great (Same page)
2. Remove a/c relay and check for power 12 volts with key on (Start or Run Only) at Pnk/Blk wire should be pin #1 of the a/c relay. (You said Check so I assume the power went to 0 volts with the ignition off?)
3. ***Is where we aren't on the same page! Blk/Red goes back to the ECU and should be a ground not 12 volts (This should be pin #2 of the A/c relay)** You said it has 14.2 volts) That's impossible! The power side of the relay signal circuit is Pin # 1....***
4. Is the load hot at all time wire The Green wire Pin # 5 of the a/c relay
5. This wire lead to your compressor clutch, Yel/Blk and should be Pin # 3 of the a/c relay and should have continuity to Compressor clutch wire!
Fred try this as well:
1. Turn ignition on don't start...
2. See if you remove the Pressure switch connector measure voltage at Grn/Blk wire it should be 12 volts....If you don't have power the wire is possible damaged or the ECU perform a pin to pin continuity check!
3. There should be no voltage at Grn/Red wire, and about 28 ohms resistance to ground!...If you have infinite resistance perform a pin to pin continuity check between pressure switch connector and the A/c auto amp
3. Short Grn/Blk to Grn/Red and your a/c clutch should engage when these are shorted...If everything checks out above this should work!
4. Start car up, you should have a/c, this tells me you have a faulty pressure switch if you can bypass it and the a/c works!
Apparently you and I aren't on the same page! Let's try it again: Scenario again is with the a/c relay removed!
1. Checking the 2 fuses.....You said you checked> Great (Same page)
2. Remove a/c relay and check for power 12 volts with key on (Start or Run Only) at Pnk/Blk wire should be pin #1 of the a/c relay. (You said Check so I assume the power went to 0 volts with the ignition off?)
3. ***Is where we aren't on the same page! Blk/Red goes back to the ECU and should be a ground not 12 volts (This should be pin #2 of the A/c relay)** You said it has 14.2 volts) That's impossible! The power side of the relay signal circuit is Pin # 1....***
4. Is the load hot at all time wire The Green wire Pin # 5 of the a/c relay
5. This wire lead to your compressor clutch, Yel/Blk and should be Pin # 3 of the a/c relay and should have continuity to Compressor clutch wire!
Hi CMax,
2) Pin #1 (pink wire)- Yes, always hot regardless of A/C on or off. I'll double check that power went off with ignition off, as I did not specifically test this.
3) I'm absolutely certain (well 99%!) that pin #2 (black/red wire) of the A/C relay socket read 14.2V. I'm not sure why this should be impossible? If I understand correctly, this pin is what the ECU sets in order to turn the A/C compressor on or off. If it grounds it, as you were expecting, then it would energize the relay and turn the A/C compressor on. However, if it's not grounding that pin when I turn the A/C on for whatever reason (faulty A/C auto amp?), then the compressor would not come on, which of course is my problem. Am I making any sense here, or am I all wet? Isn't this pin toggling between ground and hot in order to turn the compressor on/off?
4) Pin #5 (light green wire)- Yes, this was always hot regardless of switch position. I did not test it with ignition off, but I don't imagine that's important anyhow?
5) yes, good here.
Last edited by fredbanks; Jun 9, 2020 at 09:28 AM.
Fred try this as well:
1. Turn ignition on don't start...
2. See if you remove the Pressure switch connector measure voltage at Grn/Blk wire it should be 12 volts....If you don't have power the wire is possible damaged or the ECU perform a pin to pin continuity check!
3. There should be no voltage at Grn/Red wire, and about 28 ohms resistance to ground!...If you have infinite resistance perform a pin to pin continuity check between pressure switch connector and the A/c auto amp
3. Short Grn/Blk to Grn/Red and your a/c clutch should engage when these are shorted...If everything checks out above this should work!
4. Start car up, you should have a/c, this tells me you have a faulty pressure switch if you can bypass it and the a/c works!
I will have to do these tests later today after I get home from work. In the meanwhile, I do have some questions.
I did previously test at the Pressure switch connector, but I may have tested incorrectly. I checked the voltage at pin 4, which as I recall was the light green wire with red stripe. I did this test with the engine running. I read ~0V on pin 4 (light green/red wire) of the pressure switch connector, regardless of A/C on or off. Shouldn't the voltage here vary according to A/C on or off?
From the FSM schematic, I understood this to be the input to the pressure switch. Then, if the switch is operating correctly, it would pass this signal through to pin 1 (green/black wire), which is routed to pin 21 of the ECU. This is then used by the ECU to set pin 12, which is routed to pin 2 (black/red wire) of the A/C relay to control the compressor. Do I have that right?
I must be reading the schematic wrong, because as I interpret the FSM, the green/black wire should correspond to pin 1 of the pressure switch, which should be an output from the pressure switch that goes to the ECU. Why should it be at 12V if the pressure switch is disconnected?
Sorry for all the questions, but I'd like to try and understand the operation so I don't test incorrectly and waste your time. And a couple more questions if I may:
1) Where is the ECU physically located, and where can I find a pin-out on that?
2) Where is the A/C auto amp physically located, and where can I find a pin-out on that?
Thanks a lot for all your help!
Last edited by fredbanks; Jun 9, 2020 at 09:26 AM.
I don’t have all the PIN numbers in front of me can we communicate apples to apples and just test the pressure switch according to the wire color so we are speaking the same language Please?
I don’t have all the PIN numbers in front of me can we communicate apples to apples and just test the pressure switch according to the wire color so we are speaking the same language Please?
Hi Cmax, sure, I was using the pin numbers because this is how I wrote the notes when I did the testing. As I mentioned, I was pretty sure that the light green/red wire was pin 4, and looking at the PDF I attached from the FSM, that confirms it to be the case. I'm not right in front of the car right now, but since the FSM wire color coding seems accurate, I used it to update my posts above to include the wire colors at the pressure switch and A/C relay socket.
Ok CMax, so I just got home and started testing, and I have to apologize as I was mistaken in reporting my previous test results. This time I paid attention to the wire colors, and apparently I had the pin layout wrong on the AC relay. So for the A/C relay test, here are the results:Removed A/C relay, tested with ignition on/off:
Ign off - A/C Off - A/C On (3 different readings with ignition off - ignition on/A/C Off- ignition on/A/C On)
Pink wire (pin #1)- 0v - 11.8v - 11.6v
Blk/red wire (pin #2)- 0v - 0v - 0v
Lt. grn wire (pin #5)- 12.0v - 11.8v - 11.7v
I'm sorry for the confusion, and hopefully this makes more sense to you. I'll start now on the pressure switch connector test and report back...
Last edited by fredbanks; Jun 9, 2020 at 04:41 PM.
After posting those test results, I seriously question my understanding of the schematic, and think maybe I had some things backwards. If someone could give me a nutshell operation (I know you don't have time for a thesis), that would be awesome. My previous thinking was this:
1) turn A/C on at control panel.
2) This tells the A/C auto amp.to set the input to the pressure switch to a certain voltage.
3) This then gets passed through the pressure switch (assuming the pressures are correct) and to the ECU.
4) This tells the ECU to set the A/C relay input to ground, which closes the relay contact and passes the 12V through to the A/C compressor.
One thing I don't understand is that in the relay socket test above, I had 12V across the pink and blk/red wires (pins 1 & 2 of the relay). Shouldn't that have closed the contact and passed the 12V on the light green wire (pin #5) through to the yellow/blk wire (pin #3)? If I jumper the light green wire to the yellow/blk wire (pins 3 & 5), the compressor engages!
P.S.- I did test the relay, and it checked out fine
Last edited by fredbanks; Jun 9, 2020 at 06:43 PM.
2) Pin #1 (pink wire)- Yes, always hot regardless of A/C on or off. I'll double check that power went off with ignition off, as I did not specifically test this.
3) I'm absolutely certain (well 99%!) that pin #2 (black/red wire) of the A/C relay socket read 14.2V. I'm not sure why this should be impossible? If I understand correctly, this pin is what the ECU sets in order to turn the A/C compressor on or off. If it grounds it, as you were expecting, then it would energize the relay and turn the A/C compressor on. However, if it's not grounding that pin when I turn the A/C on for whatever reason (faulty A/C auto amp?), then the compressor would not come on, which of course is my problem. Am I making any sense here, or am I all wet? Isn't this pin toggling between ground and hot in order to turn the compressor on/off?
4) Pin #5 (light green wire)- Yes, this was always hot regardless of switch position. I did not test it with ignition off, but I don't imagine that's important anyhow?
5) yes, good here.
apparently pin#2 is your problem in another post you stated it being 0-0-0 in 3 ignition modes. Then you state in another 2 or 3 post that pin 2 is energized with 14.2 v. So if you have voltage at pin 1 and 2 the relay won’t work. I To work correct the pin 1 must flow to the ground provided by the ecu on pin 2. Apparently you have a wire that’s being energized by you ecu or you’re reading your VOM wrong. The relay is your problem or the relay area. The bypass test of the relay pin 3 & 5 proved that the load circuit is properly working! Check your wiring condition on pin 2 (bulk/red) back to the ecu, check your pin condition for tightness, no damaged wires,. The problem is right there in the trigger circuit for the relay! The pressure switch proves that as well jumping Grn/Blk to Blk/Red should tell the ecu to provide the ground at relay pin 2! Pull the a/c relay and test that pin 2 is grounded with the pressure switch jumper in place! Also check pin to pin test the non energized pressure switch wire back to the ecu this could be the problem as well! Is it possible to say maybe you removed some wires and got them back wards or you may have damaged the ecu pins if you didn’t back probe them but you front probed the connector and now the pin is too loose now? Check those Two wires and good luck!
apparently pin#2 is your problem in another post you stated it being 0-0-0 in 3 ignition modes. Then you state in another 2 or 3 post that pin 2 is energized with 14.2 v. So if you have voltage at pin 1 and 2 the relay won’t work. I To work correct the pin 1 must flow to the ground provided by the ecu on pin 2. Apparently you have a wire that’s being energized by you ecu or you’re reading your VOM wrong. The relay is your problem or the relay area. The bypass test of the relay pin 3 & 5 proved that the load circuit is properly working! Check your wiring condition on pin 2 (bulk/red) back to the ecu, check your pin condition for tightness, no damaged wires,. The problem is right there in the trigger circuit for the relay! The pressure switch proves that as well jumping Grn/Blk to Blk/Red should tell the ecu to provide the ground at relay pin 2! Pull the a/c relay and test that pin 2 is grounded with the pressure switch jumper in place! Also check pin to pin test the non energized pressure switch wire back to the ecu this could be the problem as well! Is it possible to say maybe you removed some wires and got them back wards or you may have damaged the ecu pins if you didn’t back probe them but you front probed the connector and now the pin is too loose now? Check those Two wires and good luck!
Well, the earlier 14.2V reading was incorrect, as I had the pin layout wrong on the relay socket. This time I paid attention to the wire colors, so I'm sure this test was right. Previously, I was reading the voltage from the wrong pin (pin 1 I believe), and with the the car running, which is why the voltage was 14.2. But those past results should be disregarded.
This time, when I did the relay test and measured 0V at pin 2 (blk/red), didn't that effectively show it was grounded? I can ohm that pin back to the ECU pin 12. Can you point me in the right direction to access the ECU and which pin is pin 12? I didn't damage any ecu pins by probing them, since I don't even know where to find them! All the testing I did was on the relay and pressure switch connector sides.
So being puzzled by the fact that I had 0V at pin 2 (blk/red wire) of the A/C relay, and given that pins 5 (lt. grn wire) and 1 (pink wire) were giving the expected 12-14V, I decided to do a little more testing. This time I tapped into the wires themselves so that I could add and remove the relay so that I could see what was happening under load. I focused on the supply side, and with the car running and a/c on, pin 1 (pink wire) was ~14V, regardless of relay plugged in or not. Pin 2 (red/blk wire) read ~0V (0.123V, to be exact) with the relay removed, but as soon as I put the relay in, the voltage jumped to 13.8V. I also read resistance to ground on pin 2, and got 3.2 kOhm with the relay out, and infinite resistance with relay in. This of course explains why my compressor is not coming on, but the question is why Pin 2 is varying?
Obviously there could be a bad connection to the ECU, or the ECU itself bad. I've been looking at the FSM and trying to interpret it, which I've obviously failed at earlier since I know now that my previous understanding of how the system works was incorrect. Going through the FSM troubleshooting, it seems to me that I've eliminated everything except the A/C relay pin 2 continuity back to the ECU, and the pressure switch continuity back to the A/C auto amp, or thermo control amp, or whatever it's called. And of course there is the possibilty that either of those 2 components could be bad as well. According to my understanding of the FSM troubleshooting steps, those continuities could check out, and a bad a/c auto amp could still be causing my problem. I tried to look into this today, and removed the glove box, but was unable to locate this unit. I'm leaning this direction, and would like to confirm it, because prior to the previous compressor failure, everything was working fine. I did not mess with any wiring from the a/c relay to the ECU, and I think I was pretty careful when removing the pressure switch harness, which appears fine visually. I recall finding the blown fuse immediately after hooking up the new compressor, which never even began to engage. This makes me think that something blew that fuse when the old compressor locked up, and I'm thinking the a/c auto amp could be the culprit. Am I all wet here? Could a bad a/c auto amp cause the symptoms I'm seeing?
P.S.- I'm eliminating a problem on the load side since pin 5 stays steady at ~14V, and I can jump pin 5 to pin 3, and the compressor runs fine.
Last edited by fredbanks; Jun 12, 2020 at 04:48 PM.
Test the relay confirm that applying power to the triggers wires closed the relay and the load has 0 ohms at all settings
Hi Cmax,
I did take the relay out and test it for continuity with power applied, and it was good. My voltmeter has an autorange, and I used that, so didn't try manual ranges, but can do.
Pin 2 is working correctly it’s suppose to be 0 volts...been saying that in ever replay! Not sure why you’re not clear on that!
Hi Cmax,
maybe I wasn't clear. I understood that Pin 2 should be 0 volts. What I was saying I didn't understand is how pin 2 was showing 0 volts, but I still wasn't getting power to the compressor?! Since Pin 2 was at 0 volts, it should have been effectively grounded by the ECU (pin 12 I believe), and my compressor should have come on. My follow-up investigation showed why that wasn't happening. Pin 2 is only at 0 volts in the unloaded condition, with the relay removed. As soon as I plug the relay in, pin 2 jumps to 13.8v (so the relay contacts don't close). This is clearly the problem, I just don't know why that is happening.
Here is where I could use some better understanding of the A/C system operation. I'm not sure exactly what triggers pin 12 of the ECU. The FSM schematics and troubleshooting don't give that level of detail, but from the schematics it looks like it's dependent on the A/C auto amp, and the troubleshooting steps seem to imply that as well. I tried to locate that component behind the glovebox where the FSM shows it to be, but I was unsuccessful in finding it. Is there a picture somewhere of this that would help me find it?
"Electrical Units Location" diagrams are at the end of the EL section in your FSM.
Thanks, that helps! So I can see why I couldn't find it behind the glove box now. It looks like it's behind the center console area, and is part of the Body Control Module (BCM). I do also see from the HVAC FSM:
"Magnet clutch control
The ECM (ECCS control module) controls compresser operation using input signais from the throttle position sensor and auto amplifier.
Self-diagnostic system
The self-diagnostic system is built into the auto amplifier (BCM) to quickly locale the cause of problems."
I did run the self-diagnostic, and it did not return any issues with the auto amp, but that may not be able to test everything. I guess I have to dig into the center console and check out the BCM/Auto amp, and probably ECM/ECU while i'm in there. I can't say I'm feeling terribly confident.
So the AC compressor on my daughter's 1996 Maxima went out, and we decided to try and replace it. It seems to just have been the clutch that locked up,and the system was operating well prior to that. I installed the new compressor, which came pre-filled with PAG oil, and also installed a new dryer, as well as new o-rings for both. Vacuumed the system down, and it held vacuum well. I added about 1.5 cans of r-134 with the car not running, then let it sit a few minutes, then turned the compressor over by hand about 10 times. Replaced the drive belt & tensioned appropriately, and locked the idler pulley in place. Started the car and turned on the AC, but the compressor would not come on (clutch was spinning, but compressor not engaged). High and low sides were both reading ~110 psi. Checked power to compressor, and it was 0V. Found a blown 7.5A fuse in the fusebox under hood on drivers side. Replaced this, and still no power to compressor. Tried swapping horn and AC compressor relays under the passenger-side hood, and this made no difference (and the horn worked with both relays). Finally, I tested the compressor by removing the AC comp. relay, and jumping across the pins (I think 1 & 2, and 3 & 5, if I recall correctly). This did engage the compressor, but I only did it for a second to test, as I was afraid to jump it for long for fear of damaging it.
The r-134 refill capacity for the Maxima is listed at 1.4 lbs +/- 0.1 lbs, which should be right at two 12-oz cans. Now, I'm not very experienced with AC, but I would have thought that with 1.5 cans added in, that would give enough pressure to run the compressor. And the pressure readings seem to indicate that. I know that low-side pressure reading was high, but that was with the AC off, and I think it normally reads high without the compressor running, right? And I would not think that with only 1.5 cans added in, that it would be over-pressurized? What do you guys think?
I'm thinking maybe it could be the pressure switch on top of the dryer, which of course I had to remove from the old dryer and put on the new dryer. I had no difficulty with this, so I wouldn't necessarily have expected this switch to fail, and it seems very coincidental. And I'm also wondering why the 7.5a fuse blew to begin with. Given what I've described, where do you suggest I begin with the troubleshooting? The pressure switch? What's the best way to test that out, and if turns out it is bad, then I guess I have to start over with the evacuation and recharge of the system?
Any guidance you can give is appreciated, and I can fill in any details I might have left out as needed.
Thx!
Besides the electrical issue, i wanted to touch on the sealed system. Equalized pressures sounds like your compressor is not running; on the off cycle your pressure should be equalized, unless you have a restriction in the system or stuck expansion/ metering device. Additionally, what is your definition of a WELL VACCUM? Did you use a micron gauge? if not, you dont know how deep of a vacuum you pulled besides your low side gauges being pinned on 30 in of mercury which could still leave moisture in the system.
with R134A gas, your HiGH side gauge will be around 125 and LOW side around 30 to 40 psi, use a PT chart to verify. Make sure you weight in your refrigerant charge using a proper digital scale, these are critically charged systems.
Last edited by maxprivate; Jun 15, 2020 at 03:38 AM.
Besides the electrical issue, i wanted to touch on the sealed system. Equalized pressures sounds like your compressor is not running; on the off cycle your pressure should be equalized, unless you have a restriction in the system or stuck expansion/ metering device. Additionally, what is your definition of a WELL VACCUM? Did you use a micron gauge? if not, you dont know how deep of a vacuum you pulled besides your low side gauges being pinned on 30 in of mercury which could still leave moisture in the system.
with R134A gas, your Low side gauge will be around 125 and low side around 30 to 40 psi, use a PT chart to verify. Make sure you weight in your refrigerant charge using a proper digital scale, these are critically charged systems.
This guy knows his stuff. But the TXV isn't the problem right now. There is no compressor function. It's a 4th gen, but the system principles remain the same. Please put another/new relay in and report back.
This guy knows his stuff. But the TXV isn't the problem right now. There is no compressor function. It's a 4th gen, but the system principles remain the same. Please put another/new relay in and report back.
yup I know. That’s why I stated Besides the electrical issue. The OP said he didn’t know much about HVAC so wanted to enlighten him a bit.
Besides the electrical issue, i wanted to touch on the sealed system. Equalized pressures sounds like your compressor is not running; on the off cycle your pressure should be equalized, unless you have a restriction in the system or stuck expansion/ metering device. Additionally, what is your definition of a WELL VACCUM? Did you use a micron gauge? if not, you dont know how deep of a vacuum you pulled besides your low side gauges being pinned on 30 in of mercury which could still leave moisture in the system.
with R134A gas, your HiGH side gauge will be around 125 and LOW side around 30 to 40 psi, use a PT chart to verify. Make sure you weight in your refrigerant charge using a proper digital scale, these are critically charged systems.
Hi Maxprivate,
thanks for the explantion. Yes, in the post you responded to the readings I took at the time were before I was ever able to get the compressor to run, so that would explain the equal pressures. From an earlier post, the last readings I took with the compressor "hotwired" were as follows:
After hotwiring AC compressor, I took readings with the car at idle, fan on low, and no recirculation Low side=25-30, high side=175-200, vent temp=42-47 degrees. Low pressure line was nice and cold & sweating, but not freezing up. High side line was warm/hot to touch. I read later in the FSM that I should have had the car at 1500 rpm, fan on high, and recirculation on. Nonetheless, I feel the charge is ok and not the main problem in any case, if at all."
These readings are still not exactly in your range, so I admittedly probably didn't optimally charge the system.
This guy knows his stuff. But the TXV isn't the problem right now. There is no compressor function. It's a 4th gen, but the system principles remain the same. Please put another/new relay in and report back.
Ok, I'll give this a try this evening when I get back home. I did try swapping the horn and a/c relays (which look to be identical) at the onset of this problem, but that was a long time ago and a lot has happened since then, so I'll give it another try.
In looking through the FSM some more, I believe I did see that the fuse that blew (located in the fuse block under the hood on the driver's side) was fuse #61, for which the heating and air FSM refers me to HA-96. Interestingly, this page seems to deal with the power and ground circuit checks for the auto amp and control unit. Hmmm....
thanks for the explantion. Yes, in the post you responded to the readings I took at the time were before I was ever able to get the compressor to run, so that would explain the equal pressures. From an earlier post, the last readings I took with the compressor "hotwired" were as follows:
After hotwiring AC compressor, I took readings with the car at idle, fan on low, and no recirculation Low side=25-30, high side=175-200, vent temp=42-47 degrees. Low pressure line was nice and cold & sweating, but not freezing up. High side line was warm/hot to touch. I read later in the FSM that I should have had the car at 1500 rpm, fan on high, and recirculation on. Nonetheless, I feel the charge is ok and not the main problem in any case, if at all."
These readings are still not exactly in your range, so I admittedly probably didn't optimally charge the system.
its probably good enough as you stated. Just wanted to clear up the sealed system, since most don’t understand it. It is an area of expertise and not something just anyone can do a fly by and get away with it working right. Your pressure and temperature ranges sound ok. The high side pressure is a bit high but as long as it’s cooling I would leave it alone. If there’s an another issue with it not cooling with the compressor running, then follow the guide lines I listed above. Most important is your vacuum and proper refrigerant charge. I would also pressurize the system with nitrogen 1st before pulling a vacuum to ensure no leaks. In any event, enjoy your cool air
its probably good enough as you stated. Just wanted to clear up the sealed system, since most don’t understand it. It is an area of expertise and not something just anyone can do a fly by and get away with it working right. Your pressure and temperature ranges sound ok. The high side pressure is a bit high but as long as it’s cooling I would leave it alone. If there’s an another issue with it not cooling with the compressor running, then follow the guide lines I listed above. Most important is your vacuum and proper refrigerant charge. I would also pressurize the system with nitrogen 1st before pulling a vacuum to ensure no leaks. In any event, enjoy your cool air
Thx, I really appreciate the tips! We've been lucky so far in that the weather here hasn't turned unbearable yet (unusual for us at this time!), so my daughter's been able to do without the a/c so far. Very soon that won't be the case, so I'll have to get this electrical problem figured out pronto!
Ok, I'll give this a try this evening when I get back home. I did try swapping the horn and a/c relays (which look to be identical) at the onset of this problem, but that was a long time ago and a lot has happened since then, so I'll give it another try.
In looking through the FSM some more, I believe I did see that the fuse that blew (located in the fuse block under the hood on the driver's side) was fuse #61, for which the heating and air FSM refers me to HA-96. Interestingly, this page seems to deal with the power and ground circuit checks for the auto amp and control unit. Hmmm....
Swapped the relay this evening, and this time I chose a different one (corner lamp relay vs. horn last time, I believe), just to double check. Still no a/c compressor engagement, and the corner lamps did work with the a/c relay.
You went around about the relays for a while and I didn't really follow along. Was too confusing. Testing a relay is as simple as the illustration on page 107 of your HA section. Or you could do what you just did (and did initially) and swap one out for a known good relay just to rule something out. The jack the relay goes into is just as easy to test, as you now have a guide as to where power and ground are located.
Last edited by User1; Jun 16, 2020 at 08:20 PM.
Reason: This illustration is from p107 of your HA section.
You went around about the relays for a while and I didn't really follow along. Was too confusing. Testing a relay is as simple as the illustration on page 107 of your HA section. Or you could do what you just did (and did initially) and swap one out for a known good relay just to rule something out. The jack the relay goes into is just as easy to test, as you now have a guide as to where power and ground are located.
To summarize, initially I "tested" the relay by swapping it with the horn relay when the compressor failed to come on. This didn't work, so I embarked on the lengthy troubleshooting. On June 9, I posted that with the relay removed, I had 12V on the pink wire (pin #1), and 0V on the Blk/red wire (pin #2). I also had 12V on the light green wire (pin 5), which meant to me that everything at the relay looked normal, and the contacts between pin 5 and pin 3 (the yellow/blk wire) should close and pass the 12V on to engage the compressor. My first guess would have been a problem with wire from the relay to the compressor. However, given that I had already successfully jumped the compressor by manually jumping pin 5 to pin 3 multiple times, I ruled that out. So my next thought was the relay. In that 6/9 post, while I mentioned that I tested the relay, it's true I didn't really say how I tested it. But I did test it according to the diagram you posted above. It checked out good.
Now I was really puzzled, so I probed into the wires for pins 1 & 2 so that I could monitor these signals with and without the relay. With the relay removed, everything tested just as I mentioned above, and as should be expected. As soon as I plugged the relay in, the voltage on pin 2 of the relay jumped to 13.8V. So under load, the relay is no longer being energized. Now pin 2 of the a/c relay comes from pin 12 of the ECU, so the wiring there could be an issue. Since by replacing the compressor I didn't disturb this wiring, I was thinking this was not a likely suspect, and was thinking instead either the ECU or the BCU/ A/c auto amp. The FSM troubleshooting steps also seem to imply to me that these 2 are possibilities given the other steps I went through already. Then, when I think back to finding the blown 7.5a fuse, that lead me to post this:
"In looking through the FSM some more, I believe I did see that the fuse that blew (located in the fuse block under the hood on the driver's side) was fuse #61, for which the heating and air FSM refers me to HA-96. Interestingly, this page seems to deal with the power and ground circuit checks for the auto amp and control unit. Hmmm...."
Console switch/control module was my gut feeling in post #10. They are easy to remove and cheap if you have a yard nearby. Self-Diagnostics didn't return sensor issues. I was concerned about the resistor, but it appears that being auto-AC, you don't have one. The auto amplifier is built into the control module
For reference for that part #, which states it is a "manual controller", but they all read that way. I wouldn't get too hung up on the wording if it looks the same as yours.
Thx, that looks like it. I'll do some checking around local yards, and keep this as a backup if I end up needing it. I appreciate your help with this. Hopefully we've honed in on the issue, and are close to getting this solved. Will dig into these hopefully last steps when I can, and report back.
So I found a console unit at a local yard today, and gave it a shot tonight. Unfortuately, no joy in Mudville, and the compressor still did not engage. I had been thinking about this over the past few days, and I have to admit I had become skeptical this would solve the problem. As I thought back through the troubleshooting steps in the FSM, everything seemed to point me to the auto amplifier. I believe I initially misunderstood User1's post and was thinking that he was saying the auto amplifier was built into the console control unit, so this gave me hope the console unit could be the problem. I should have questioned that further, since earlier in the troubleshooting steps I posted it stated the auto amp was located in the BCU. This was the unit I was mistakenly looking for in the glovebox area before (I forget now where I saw that to be the case), so I could troubleshoot it.
Anyhow, one good thing about taking the console unit out is that once this is done, the BCU is easy to see and remove. I went ahead and took it out and inspected it visually to see if there were any obvious trouble spots, but no such luck.I'm still betting this is the issue, so will try to find one locally and swap out to see. If not that, the last possibility I can think of is the ECU. I'm not sure what the likelihood of that failing is? In my reading, I did see on this forum that the the 4th gen BCUs were prone to failure (not necessarily for this problem though), so that's another possible vote towards the BCU.
Another good thing about taking the console unit out is that since I had to take the stereo unit out in the process, I finally got around to fixing the dead display on the stereo (thanks to a nice tutorial I found on this forum from MadChef about resoldering a power board). I'm learning a lot more than I really cared to about this vehicle!
My next step will be to swap out the BCU, unless someone has a better idea?
By A/C controller do you mean the dash control? I went through all your checks, so let me try to respond to those:
