I haven't touched my A/C all winter and finally tried it out today. Ran into a bunch of problems.

First, my compressor wasn't activating. I'm thinking maybe it needs to be recharged. Hooked up a guage to the low side and the PSI shot straight up. It hit about 80PSI. It was about 80 degress here today. From searching, normal PSI should have been around 25 give or take.

My question is what would cause the high PSI?

I'm not even going to attampt to add refridgerant.

The blower and heat is working.

 

What was the reading on the high side? Don't mess with anything until you factor that in.

 

Only tested the low side.


1234char

 

If the A/C compressor was not engaged (not actually turning) when you took the reading, 80 PSI would be a correct reading if the system was fully or even somewhat charged. Low and high side pressures would measure the same in this case.

Does the compressor engage at all, even for a short time?

 

Hmmm... i didn't know that the high and low are the same if the compressor doesn't engage.

The compressor didn't engage at all. Not even for a second.

I'm leaning towards fuses and relays now.

Anything else I should look for?

 

Assuming you are in "auto" mode and not "Econ" mode set to the appropriate temp., then fuses and the A/C relay would be the next step. After that check, a voltmeter on the compressor connector can confirm it's an electrical issue vice a compressor clutch issue.

 

Thanks for the input....

I'll take a voltmeter to the connections tomorrow. I did a quick check and the fuses are fine. Hopefully it's not the compressor.

 

I'm troubleshooting another A/C system for another org member and i've hit a wall. We have checked both 10A fuses and switched the relay with the taillight one. All checks out. When we take a voltmeter to the A/C power connection, we get nothing.

Aside from a wire being melted or broken, where else could the circuit open up?

Am I right to assume that power should be going to the A/C regardless if the compressor is working?

The car is getting about 80PSI on the low and high side. I read before that the low side should be the same as the high side if the compressor isn't working.

 

Maybe the AC control unit in the dash is bad or something got disconnected there?

 

He was going to run the diagnostics tests on the control unit when he got home...

Zero... you in here man?

 

Here, tried to do the tests, couldn't get the hang of it. Which ones in the diag test list should I perform? I printed out the sheet from the FSM.

 

Is the other system you are testing the manual or auto temperature type? Also, for the A/C power check you are doing: is it just power to the compressor connector or are the fans dead too?

 

We tested just the power to the compressor. Everything else is working.. I.E. Blower, heat...etc.

 

This may be too simple...Did you check he fuse box? When my A/C stop working, it was a loose fuse that was the problem.

 

We have checked both 10A fuses and switched the relay with the taillight one. All checks out.

 

anyone know what the pressure should be when compressor is engaged? i don't quite remember, but high side should go up to 130's i think...

 

Check the fuse for a secure fit and both fuse prongs make definite contact within the fuse box....if that checks out then....All checks out.....

 

Low side should be 30ish.. give or take a few psi... depending on temp

Checked a few times

 

wngan9447,
For your "other A/C problem -- if its the Manual A/C system (not the AUTO model that you set the desired temp digitally) the check you already ran was to start the Max, select a vent setting (defrost or other), turn the blower fan on, turn the A/C switch to "on" (light below switch should illuminate) at which time you had no A/C clutch engagement as per the FSM diagnosis sheet - Right? You then verified refrigerant pressure in the system and a 'no voltage' condition at the A/C clutch connector and proceeded to swap out both the A/C fuse and relay located under the hood -- the A/C is still inop and the swapped components worked fine elsewere in the Max - also right? In the Max's Manual system that would leave the related A/C wiring, the A/C control unit, or a defective or disconnected refrigerant transducer sensor as the culprit -- all petty rare in a Max, but stuff happens. You might investigate any recent work done on this vehicle.

Now if it is the AUTO A/C system, there are other things that would inhibit the compressor from engaging. Its a complicated beast - a bad outside air or interior air sensor/sensor connection can disable the A/C.

Good hunting

 

Yes to everything you said here.

Good suggestions... we need to look into this more. There has been recent work done, but Zero needs to tell you that. I don't know exactly what it was.

It is an Auto system in the car. I do know that if you set the temp at the lowest possible setting, the A/C should engage regardless of the interior temp.

Thanks for the input

 

For the AUTO system, make sure that the ECON switch is off - ECON 'on' will prevent the A/C from engaging on the AUTO system. The interior temp and outside temp should be readable inside the Max. An open circuit on either of these would give a a -34 deg (or so) reading on the respective circuit and prevent A/C engagement regardless of the Temp setting.

 

Weird Problem, Today It reached almost 100 Degrees, A/c Worked great in the morning, then all of a sudden the compressor stopped working. I turned the whole system off for a minute turned it back on and the compressor kicked on for about 1 minute then shut off.
This is on auto, Recirculate and fan on high I like it cold...So I turn the fan down still on auto and recirculate...Ran fine...As soon as I turn the fan on high the compressor shuts down and I get warm air blowing...It wasnt such a big deal but the ride home from work I thought was going to be a hot one. So I turn the ac on recirculate, and I start driving, Everything is fine, Fan on high...Got home checked the low side and the psi is at 25... it was 97* on the Outside temp today, Should I add refrigerant, Im not actually sure on what psi it should be at. My friend has a manifold guage that I will check the high side make sure its not clogged somewhere, later when he gets out of work.

 

Without the A/C on the low side should be at 90-100 PSI.

To check A/C charge, bring down the windows, put the A/C in max with highest blower setting at the engine at 2000 RPM idiling. Then connect the gauge to the low port and it should show between 35-45PSI, anything less than that needs recharging. When recharging one should be careful, when the compressor clutch engages it sucks the refrigerant and compresses it. It should show anywhere between 35-45PSI and when the compressor is not engaged it should be in the high 70-80PSI.

Be slow when charging the system, it take very less ozs to overfill the damn tiny system capacity (capacity is 1.2 lbs in total).

 

Does anyone have an illustration of the A/C lines to show the "low" and "high" sides? Thanks in advance.

 

The one close to the condensor is the high side and the one near the PS reservior is the low side port.

Now there are 2 plastic caps clearly highlighted "H" and "L" letters on top. You cannot stick a recharge kit to the H side since the port dimensions are different (the recharge kit will not fit the H port line).

 

at the end of last summer i felt my ac go from freezing to cool

tried charging it for the 1st time a few days ago
reading was on the low side of good - 25psi or so
put in at least 7oz of r134 and it didnt even dent the psi reading - still 25
i did not try putting in the rest of my can
do i have a leak or should i put in more?

 

I recharged my vehicle last weekend for the first time and it took a whole 12oz. I would put in another oz or two till it comes to 35-45PSI. Be slow and shake can vigorously while refilling.

 

As far as I know about a/c systems, the compressor should get no power unless the high pressure switch and the low pressure switch tell the system to go on. You have to check for power on those switches first, then the compressor.

 

To do a partial recharge, the safest way is to add refrigerant to the low side while running is with the can upright and put it in a bucket of warm water while doing this so its temperature is maintained. Be careful not to contaminate the system with water while changing cans. Sealant is bad, don't add it.

Birken

 

BTW, you can't really add refrigerant to the high side. It will blow the can of R134 open and probably kill the person doing it.

Actually, there isn't any GOOD way to do a partial recharge because you have NO idea how much refrigerant is in the system so adding more may help or hurt. Also, adding R134 with those off the shelf setups will introduce air into the system unless you are super careful to bleed the air out of the charge hose before connecting it to the A/C line.
Also, it is not possible to measure JUST the low side pressure and know if you've added enough or too much R134. Especially on a Nissan A/C system. They are designed to maintain a constant low side pressure even in the worst conditions.

The only really good way to handle your A/C is to have someone evacuate and recharge it. The cost is easily offset by the fact that your MPG will totally suck if you overcharge your A/C and your compressor will fail if you have too much R134 in your system.

I've done partial recharges to a number of cars and the end result is always the same. The A/C works better for a while but never as good as it should. Even using manifold guages you can only get so close to the proper pressure and it's near impossible to tell if you have the appropriate fluid level. Plus, the issue could be moisture in your system or a bad receiver/dryer. Partial recharding doesn't fix any of that--just makes things worse.

Evac and recharge is the best way to go. It costs about $125 at the stealer.

If you absolutely MUST do it yourself--this guy has a good writeup on it: http://www.firstfives.org/faq/AC/ac_charge.html

 

Finally, some no-nonsense advice to all of those people who think that every cool/warm AC just needs a shot of refrigerant.

It's not just that simple. If it were, everybody would be an AC technician and the ones out there making a living at it would not be able to charge such high fees for diagnosis & repair. It takes knowledge and equipment to do it right.