Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

A/c stops cooling at traffic lights

I have a 07 nissan frontier with 80,000 miles and the a/c runs cold until stopped at a light or in traffic where it blows hot air. I am in Texas and it’s already close to 100 degrees I need HELP!!! Had the same problem 4 mths. ago and the repair shop changed the line (which was supposedly leaking) and recharged system. Now same problem, took it back to the shop and they now tell me my compressor is going out??? I find this hard to believe. Any help out there?

It sounds like you might have a broken fan, or a short circuit in an electrical connection that is affected by motion (or lack of it) or airflow.

If it turns hot as soon as you stop, then it is a vacuum problem. The blend doors in most cars today and controlled by vacuum. The available vacuum varies with engine speed and load. Often if there is insufficient vacuum (not uncommon when you come to a stop) then it may not be able to hold the blend door in the A/C position and so it defaults to the heat position.

Manifold vacuum is highest when the car is at a stop and at idle. It goes low when the throttle is opened. And its not the hot/cold selector that defaults when there is a loss of vacuum it is the vent that the air comes out that defaults to the defroster position.

You very well could have a compressor problem. Ask for more details why the shop feels the compressor is at fault. Are they basing their diagnosis on pressure readings or are they detecting leakage?

Your cars AC system could very well be controled fully by electric motors and not have a vacuum component at all.

No reason to doubt the shop yet.

After the line replacement and the original problem coming back I called the dealer and they thought it might be low on freon or water causing the fail switch to shut off the compressor on an overheat. When I took it back to the shop they did a pressure test on the freon which was fine and then listened to the compressor with a stethoscope.

So why are they condeming the compressor?. If pressures are fine and the compressor is not noisy or leaking why are they saying the problem is the compressor?

I’m not sure, can you hear the compressor making noise with a stethoscope? They quoted me $1775.00 to fix it maybe they saw me coming and times are hard? I just moved here and have no experience with shops in the area. Have an appointment with an a/c guy recommended from the people on here but they have a 9 day waiting period. Everyone else wants $100.00 to diagnose it and a few days wait.

I have seen compressors go bad, not because of mechanical problems, but because of electrical problems. Sometimes, these electrical compressor problems seem to express the same symptoms you are having. For some reason, the electrical connection (harness) connects while the car is in motion, but the connection fails as soon as you get off the highway or stop at a light. Take a look at the wiring that leads to the compressor. With the engine running and the air conditioner on, CAREFULLY move that cluster of cables around a little and see if the compressor cycles on and off. If it does, you need a new compressor.

PS- It might be easier and safer to move the wires around with some kind of reacher, rather than stick your hand in there while the parts are moving. If in doubt of your safety, don’t do it. Instead, ask a professional to check this for you.

You can hear much more than you want with a stethscope. The price you are quoted is a red flag,this shop is out. You would do yourself well to wait the 9 days.

Check what you can check. What can you check? The fan. You might have one or two. They are right behind the engine radiator, sometimes in front of it and you can see that one through the grille. If you turn the AC on and the fan doesn’t ever work, the AC won’t work. If your AC is warm and the fan isn’t turning, you found the problem. If the fan is turning and the AC is warm, the problem is somewhere else.

My first guess is that the cooling fans aren’t working.

It’s very difficult to make much of a guess on A/C problems without knowing the high and low side pressures.
A failing compressor should have an affect on those pressures.

What you might consider is the possibility of a failed thermal control amplifier. These have been somewhat problematic anyway.

Hi, have you resolved this issue? I have the exact same issue with my 99 Subaru Forester. I live in Miami, Fl. and our days are usually 95-100. I find myself putting my car in neutral and revving over 2000rpms in order to cool at stops.