Most of my cars have been ready to replace when the AC starts acting up. My 2001 SE with nearly 180K is running great and is still fun to drive. Unfortunately, the AC has been struggling to blow cold air unless I'm driving down the road. When I come to a stoplight, the air becomes noticeably warmer but not hot (like drawing outside air). My first thought was that the freon is leaking.

Armed with a gauge and a can of R134a, I tested the pressure at the low port. The instructions said that the pressure should be between 25-45psi. When I gauged the pressure it read 75psi (!). I bled the system to lower the pressure to 45psi figuring that an overcharged system may be the culprit. This was not a good morning to do this since the humidity is nearly 100% with a heat index of 90F.

The compressor runs without cycling but there is absolutely no cold air now. You can hear high pitched "static" noises coming from the dash (like fluid flowing) that was not there prior to being drained.

Does anyone have any ideas?

 

45 PSI seems kinda high for a Maxima, mine runs at a PSI of 30-35 PSI and the air comes out pretty cold. I bet your a/c is still overcharged.

 

I just think it's strange that it *was* blowing cold consistently, then blowing cold when in motion (at the high psi), and no longer blowing any cold air at 45psi. What's the proper way to check the pressure? (could I possibly be goofing that up?)

 

When you tested, did you have the A/C on high setting? I think that is necessary for the the test. It's been a while since I did mine.

 

The way to check the pressure is to turn the a/c to the coldest setting, turn the fan to highest setting, and turn on the air circulation. Let the a/c run for 5 minutes then check the low pressure psi. Watch the guage for about 5-10 minutes and make sure the pressure stays at a steady pressure, if it goes up and down then your compressor is shutting off and on which means it is overcharged. Make sure you have the hose connected properly.

 

Perfect advice (which I had not done correctly). I will do this and follow up with the result.

 

When my AC was only blowing cold while moving, I had a weak compressor. Replaced the compressor and I am all good now. It would blow mildy cool at a stop light but was significantly less than when moving. You MAY have the same problem.

 

Cold A/C only when driving and high pressures when stationary point to an airflow problem usually. Is your condenser fan working?

 

My condenser fan is working properly (as it was the first thing I checked). 2brosgixxer may have a point regarding my compressor's useful lifespan may be reaching its final stages (logical but never considered it). I wanted to tackle the test last night but had class. So I'm driving without AC again today. This evening is free so I will be tackling it.

If low freon was the original problem, I hypothesize:

1) I checked the "static" pressure of the system while it was off hence the abnormal reading at the low pressure port. Further Googling, along with replies to this post, show that the static pressure will be much higher when the system has been at rest. Since I tested after the car had been sitting overnight, this would be the case.

2) I bled the system in an effort to lower the pressure. If freon was already running low, then I exacerbated the problem by bleeding more freon out of the system.

3) I believe the leak is at the pin valve at the low port since when unscrewed the cap (L) a little bit of UV dye sprayed (but not constantly). It may be weeping a bit.

4) If I properly charge the system to 35-45psi (45-55psi if it is very hot outside), and the air continues to blow lukewarm at rest but cold in motion, I believe 2brosgixxer solved my problem at the expense of additional freon and a compressor.

My third gen Maxima lasted to over 300K miles before I purchased this one. It has been babied with synthetic oil changes for its entire lifespan, and the engine can still break loose the tires on demand. The rear bumper is starting to lose its clear coat, but the rest of the car is in good shape. I'm trying to keep this old girl on the road until the wheels fall off because living car payment free is a wonderful thing.

Thank you all for the feedback. Updates forthcoming.

 

I suppose I should have looked at the pressures much sooner. I check the pressure of the low side court and discovered a pressure reading of around 20 pounds. I emptied a can and a half of Freon into the system and was able to get the pressure stabilized between 38 and 30 PSI. The car blows ice cold now.