Automotive Air Conditioning Information Forum

Basic info:

1999 Nissan Maxima
Location: Phoenix, AZ
Low temp: 70 - 75 (1500 RPM)
high side 180 - 200 (1500 RPM)

All of a sudden my A/C stopped cooling very well. The temp in the car would fluctuate from 50 to 80 degrees. Tested the pressures and low side was around 50 and high side was around 150. I replaced the Refrigerant control valve (RCV) on the A/C compressor and the expansion valve. I heard fluctuating temps like this could possibly be due to the RCV in the compressor. Well this seemed to help for a while. Temp would get down to about 48 and wouldn't jump around like it had before from 50 to 80. This didn't last long though and pretty soon my temps were a constant 60 coming from the vents. Now the pressures were about 60 to 70 on the low side and 170 for the high side. I had put in UV dye previously and there were no signs of any leaks near the evaporator behind the dash or anywhere in the engine bay. At this point I decided to replace the compressor.

New compressor in and same thing is happening. Pressures are around 70 - 75 on the low and around 200 for the high side when the engine is at 1500 RPM. Looking for some advise on what else may be causing the problem? I think i've ruled out compressor since i'm having the same issue with this new compressor. I'm leaning towards the TXV but that was replaced when i did the control valve but maybe I got a dud?

One other thing, when the cooling stopped working correctly I get kind of a musty smell from the A/C. Not terrible but definitely doesn't smell like it should with a properly working A/C. Not sure if that would help with diagnosis at all. Also, when I recharge I do pull a vacuum before filling by weight. Car takes about 23 oz so I just put 2 cans in which should be just about right (and it has been in the past when I had a faulty compressor a long time ago).

Hope someone can help with the next step in figuring out the issue as this phoenix heat is a killer! Thanks!

**SOLVED**

Ended up replacing the TXV since I would be able to check the blend door at the same time to see if heat was mixing in. Blend door was closing fine blocking off any air from going through the heater core. New TXV and I could tell right away when adding refrigerant it was looking better. This time the low side would drop to about 35 to 40 whereas before it was in the 60 to 70 range with the first can. After adding the 24 ounces the low side was around 40 and high side was 225 which are much better pressures than before and the vent temp would get down to 45 - 50 degress (albeit it does take it awhile but that could be due to the 110 degree weather). Drove it around and seems to stay in that 45 to 50 degree range which i'm totally fine with. Not as cold as some vehicles but I think that is about right for this vehicle if I remember correctly.

Thanks for all the help everyone!

Your Low side too high and your High side is too low. Is the fan working at the condenser and is the condenser relatively clean - not clogged by debris? Yes - you pull the vacuum first and then charge.

Yes both fans are running fine and no major debris on the condenser, just some bugs and things like that.

H – too low
L – too high
Low refrigerant level or failing compressor

With the gauges connected, rev the engine to 2000 RPM and watch what the pressures in the AC system do. Do they move closer together (high side gets lower while low side gets higher) or do they move away from each other? If they move away from each other, start with evacuating and recharging the system and retesting.

If they move together, you have a weak compressor and it is recommended to replace the system. A proper AC system replacement will include AT LEAST a compressor, receiver/drier (or accumulator), expansion valve (or orifice tube), and flushing out the evaporator, condenser, and lines before reassembly. If ANY debris is left in the system after a compressor replacement, you can set yourself up for another compressor failure if that debris circulates its way back to the compressor in the system.

If you're in north Phoenix, I'd take to Smart Automotive on north Cave Creek Rd.

If you're south or in east valley, take to Salem Boys Auto in Tempe.

Folks form the north don't realize that a 1999 vehicle in Arizona can still be pristine.

Thx robmaxfli and Cusser. I'll give those things a try. I'm in the east valley (Mesa), I appreciate the shop recommendations. Hoping to fix this myself though (not urgent as working from home so don't really need to use it much).

Hoping there is a way to pinpoint the cause. The compressor is brand new and symptoms are exactly the same as before so I'm leaning to it being something else and hopefully I didn't get a bad compressor. It has the correct amount of refrigerant in it currently and I added it correctly (pulled vacuum and purged the hoses first). What would the next logical thing be that would be causing this if it's not the compressor? Any other ideas?

I'll try to get the pressuers again at 2000 but I think the ones I listed before were probably between 1500 and 2000 so they will probably be pretty close to those as same numbers.

Thank you AI9 for the additional info!

Just an update after performing pressure tests again.

Testing in garage but outside temps were about 113

At IDLE (800 RPM)

Low Side: 50-55
High: 220
Vent Temp: 70

At 2000 RPM

Low Side: 60
High: 225
Vent temp: 70

One thing I would like to point out is the low side line feels ice cold like a can right out of the refrigerator. The vent temp stays around 70 but still has a funny kind of musty smell to it. Hopefully this will help diagnosis. I think my next step is going to be replacing the TXV and flushing the lines and evap core. Maybe even replacing condenser since it is original to the car and is only 50 bucks for a replacement. Unless anyone has any other ideas?

THanks for all the help!

cmilot6329 wrote: Vent temp: 70

One thing I would like to point out is the low side line feels ice cold like a can right out of the refrigerator. The vent temp stays around 70 but still has a funny kind of musty smell to it. Hopefully this will help diagnosis.

Hold on - if the low side line at the evaporator is ice cold, then that directs towards warm/hot air getting into the system, like a flap/door not closing completely and letting in warmer air from the heater core or from your hot garage.

Interesting, ok so these pressure seem pretty good at this point? I'll have to see how I'll be able to check any flaps/doors to see if warm air is missing in with the cold air. Would that mixture of hot and cold air explain the musty smell?

Ok checked the air mix door actuator under the dash. I can see when I move the slider from hot to cold it is turning and opening and closing the air mix door properly and all the way. So doesn't appear hot air from the heater core is getting mixed in.