Air conditioning running warm/hot when at idle, but USUALLY cools down when I accelerate


I have a 1997 Nissan Altima. The AC has always been cold. Now I am finding that the air coming from the AC has sometimes started to blow less than cold (at times almost as if the air is blowing from the vents with the AC turned off) but typically when I am at idle. Usually when I accelerate it gets cold again, but not always immediately.

Normally I would think the AC needs freon, but is it normal that the cold would go in and out the way I described? Please let me know if it sounds like I need freon or something else might be going on. Thanks.


It lasted 10 years…That’s all you get.


Not unusual for the refrigerant to need recharged after 10 years. Call around for prices for a leak check and recharge. Can be a wide difference in prices. I would skip Pep Boys, dealers, and chain shops.


I had this problem, and it was the cycling switch that needed replacement. This is the part that is supposed to shut it off when you are accelerating. It had lost its detent.


You really need to have the gauges put on it and see what’s going on.
It could be just a low refrigerant charge. At idle the low side pressure is up and the high side is down.
The evaporator temperature is roughly equivalent to the low side pressure so you can see how the low charge could affect this.

At higher rpms the high side goes up, the low side goes down (translating to lower temps) and also, at speed you have additional air moving through the condenser.


Another possibility to check is leaves or other debris that might be blocking airflow through the A/C condenser (in front of the radiator). Also, check that the electric radiator fans are working properly.


Caddyman, wow. That’s the best advise you could come up with? Big of you, man.


It’s probably down by a bit of freon. If it happened abruptly, then you may have sprung yourself a nasty leak. But it’s worth gauging and refilling if it’s low. It’ll only cost you a bit, so if it leaks out it’s no big loss. An A/C shop will be able to diagnose with a manifold gauge set.

Don’t be too quick to buy any of their catastrophy stories.



Could be a bad reed valve in the compressor. Gauges can help determine this. Higher rpm’s it will pump enough to cool, but at a stop or slow traffic it never builds enough pressure for adequate cooling. HTH.


Jesus Christ! Ignore Star’s incoherent ramblings about A/C repair. None of it applies to automotive A/C work and yet he continues to steer people off the cliff with wrong directions.


Condenser fan/assembly/motor may be dying. I have a montero sport that had the exact same problem. The condenser needs air flow to keep the freon cool. When the car is in moton, you get that air flow.

Picked an aftermarket fan assembly for around a hundred bucks. Pretty easy to install - half an hour - and AC works as good as new.


I had identical symptoms on my 93 Sentra. I had a hole in my condenser…maybe from a rock? I now stay away from dump trucks as much as possible. I wish I would have went to a different shop, or skipped repairs all together. Most of one summer and over $700 of parts and repairs and still no A/C.


Easiest thing to do is look to see if the AC fan is running. There are 2 fans under the hood…one only runs when the AC is on. I had the same problem years ago. Turned out the connector to the condenser fan had come loose. If that’s it, you’ve saved some $.