Help needed: A/C charging question - Long
09-30-2010, 09:15 AM
#1
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Help needed: A/C charging question - Long
Our Max is starting to blow cool air even at lowest temperature setting, similar to what some of you here in the forum are experiencing. I performed the AC diagnostic with a 25 code. Flaps are working fine, so is the compressor (it clicks and kicks in). I checked the low side pressure and it was only 35psi with ambient temperature at 90°. According to specs it should be 50-55psi at that temperature, so I thought recharge time!
So this is where it gets weird and I would appreciate your feedback. I added about a can till the gauge read 55psi; the low side tube was cold, so I know it was entering the system. But, it still blows cool, not cold in the cabin.
I let the car rest awhile and after dinner I tested the pressure again and it was now at 60psi - knocking on the red zone, according to the gauge reading. But the car's still blowing non-icy air and the low side is warm/hot to the touch still. Because of the latter symptom, I'm tempted to add another can, but the gauge readout is scaring me from doing it.
What do you think?
So this is where it gets weird and I would appreciate your feedback. I added about a can till the gauge read 55psi; the low side tube was cold, so I know it was entering the system. But, it still blows cool, not cold in the cabin.
I let the car rest awhile and after dinner I tested the pressure again and it was now at 60psi - knocking on the red zone, according to the gauge reading. But the car's still blowing non-icy air and the low side is warm/hot to the touch still. Because of the latter symptom, I'm tempted to add another can, but the gauge readout is scaring me from doing it.
What do you think?
09-30-2010, 10:01 AM
#2
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First off you are now way overcharged. Low side should be around 35 PSI which was were it was in the first place. Where did you get 55 psi from?
The only way to correctly recharge R134 systems is by weight, and from a completely discharged and vacuum state.
Have an A/C tech look at the system, there are many more reasons for a system to perform poorly other then it's R134 charge which you now have completely messed up.
The only way to correctly recharge R134 systems is by weight, and from a completely discharged and vacuum state.
Have an A/C tech look at the system, there are many more reasons for a system to perform poorly other then it's R134 charge which you now have completely messed up.
09-30-2010, 12:38 PM
#4
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Location: San Antonio, TX
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I live in San Antonio... ITS HOT here. I had issues the same thing. It showed around 50-55. I loaded a can in my system and while I was charging it the car was ARCTIC cold. But right after the Compressor was kicking in with a sever sound. It was working through the higher pressure, I think I did over charge it. However, before all this I had my mechanic look at it after I had the compressor replaced and he said the charge seemed right. It has NEVER gotten super cold like it used to on the original compressor. I think it has to do with the age of the vehicle, probably had a super small leak and just the nature of the new coolant, its not as good as real freon. But once my pressure was too the right levels it works OK. Not great but OK for Texas weather. still takes about 5-7 minutes to blow cold air from a hot day. Replacement compressors not as good as original equipement? did 4th gens use older forms of coolant?
09-30-2010, 12:42 PM
#6
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also, be careful charging your system or whatever. Its crazy illegal if you get caught purging your system into the open air (although I don't think anyone would do this on purpose, just saying) . Its recommended a shop do it for you with a vacuum system. Have a shop officially check your levels, low end and high end pressures.
09-30-2010, 12:47 PM
#8
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Thanks for your reply. Blocked with leaves, debris and bugs, you mean? I was just thinking about giving it a hose down, but when I visually inspected the area yesterday is was a little dirty, though I don't think that would create the symptom I have right now.
09-30-2010, 12:54 PM
#9
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I was actually thinking of your lines. Its a closed system, so if outside debris was in there you probably would have NO a/c, but since you said its getting cool air just not cold, I think its either your pressures are too high or too low and the unit is not pushing the coolant through the system correctly. When I over charged my system would kick in with a REAL ugly sound and almost immediately cut off, somehow it regulated itself after a few days and is where it is now. If you got a mechanic you can trust JUST to check levels and not purge and refill your system I'd do that. or just buy another can, and use the valve gauge that comes with it and see what it reads now after you have fooled with it already. I keep the valve gauge in my trunk
09-30-2010, 01:53 PM
#10
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From The On-Line Automotive AC referance Guide
Again, where did you get 50 psi from? Your way overcharged.
Take it to an A/C tech and have the system diagnosed. Your R134 charge is WAY OFF.
When charging, what should my low and high side pressure be?
Ah, this is the most asked question there is. There is no magic answer for this question though. There are too many variables. Compressor (engine) RPM and airflow across the condenser are always changing, thus engine speed is always affecting pressure. System design, blower speed, mode setting, refrigerant type, all cause variance in high and low side pressure. For this reason we simply can't say 30 on the low side and 200 on the high side. Though I might add, that's about where you'll usually end up. The reason 30 psi on the low side is just about right is because that translates into an evaporator temperature somewhere around the freezing point of water. Look at your low side R12 gauge and you'll see a temperature scale right next to your pressure scale. That low side pressure translates into evaporator temperature. Since moisture collects on the evaporator, we would like to keep the evaporator temperature slightly above the freezing point. R134a low side pressure will be be slightly lower (27 PSI) at this temperature. Again, refrigerant type is one of those variables we have to consider.
Ah, this is the most asked question there is. There is no magic answer for this question though. There are too many variables. Compressor (engine) RPM and airflow across the condenser are always changing, thus engine speed is always affecting pressure. System design, blower speed, mode setting, refrigerant type, all cause variance in high and low side pressure. For this reason we simply can't say 30 on the low side and 200 on the high side. Though I might add, that's about where you'll usually end up. The reason 30 psi on the low side is just about right is because that translates into an evaporator temperature somewhere around the freezing point of water. Look at your low side R12 gauge and you'll see a temperature scale right next to your pressure scale. That low side pressure translates into evaporator temperature. Since moisture collects on the evaporator, we would like to keep the evaporator temperature slightly above the freezing point. R134a low side pressure will be be slightly lower (27 PSI) at this temperature. Again, refrigerant type is one of those variables we have to consider.
Take it to an A/C tech and have the system diagnosed. Your R134 charge is WAY OFF.
10-01-2010, 09:44 PM
#11
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I can vouch that the 50 psi is straight from the side of the can of R134 coolant. It says with an ambient temperature of 90 degrees, pressure should be around 50-55 psi and registers in the "green" zone on the provided valve gauge.
10-02-2010, 12:56 AM
#12
Ambient air temperature is at 86degF, your high side pressure should be around 169-225psi and your low side pressure should be around 21-26psi.
Ambient air temperature is at 95degF, your high side pressure should be around 199-262psi and your low side pressure should be around 23-27psi.
Hope this helps.
Ambient air temperature is at 95degF, your high side pressure should be around 199-262psi and your low side pressure should be around 23-27psi.
Hope this helps.
10-02-2010, 10:33 AM
#13
10-02-2010, 12:40 PM
#14
The data I provided above is from the FSM.
You are missing the point. Nissan designs the system to operate at a particular pressure. Why would you trust what it says on the side of a can of GENERIC R134a refrigerant? You should consult the FSM for the correct procedure and specs to charge the a/c system...and stop believing everything you read on a can of crap you bought from Autozone.
10-02-2010, 02:06 PM
#15
Yeah, I know. I just wish people would read things for themselves. There would be less silly little arguments here if people would read and research what they're arguing about.
Also from the data you provided it is obvious that you need an a/c gauge set to read both high and low sides...which these people aren't doing. The refill gauge on a can that is sold in the part stores is the WRONG way to go about this job.
Also from the data you provided it is obvious that you need an a/c gauge set to read both high and low sides...which these people aren't doing. The refill gauge on a can that is sold in the part stores is the WRONG way to go about this job.
10-02-2010, 02:08 PM
#16
Yes, manifold gauges are required before working on any AC system.
Yeah, I know. I just wish people would read things for themselves. There would be less silly little arguments here if people would read and research what they're arguing about.
Also from the data you provided it is obvious that you need an a/c gauge set to read both high and low sides...which these people aren't doing. The refill gauge on a can that is sold in the part stores is the WRONG way to go about this job.
Also from the data you provided it is obvious that you need an a/c gauge set to read both high and low sides...which these people aren't doing. The refill gauge on a can that is sold in the part stores is the WRONG way to go about this job.
10-02-2010, 06:18 PM
#19
Why don't you use the real manual? Those Haynes and Chilton manuals suck!
http://www.nicoclub.com/FSM/maxima/1997/
http://www.nicoclub.com/FSM/maxima/1997/
10-03-2010, 03:09 PM
#20
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Why don't you use the real manual? Those Haynes and Chilton manuals suck!
http://www.nicoclub.com/FSM/maxima/1997/
http://www.nicoclub.com/FSM/maxima/1997/
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