2000 Honda Civic Air Conditioner Issue

I have a 2000 Civic EX and the air conditioner is driving me nuts. I have had the car for about 1.5 years and last summer I noticed that on days when the temp was above 80 degrees, the air conditioner blew cold air only when I was driving above 50mph. At speeds below 50mpg, the AC blew cold air for a few seconds and then warm air for a few minutes and this would repeat until I got back up to above 50mpg.

I tolerated this last summer but decided to address it before the hot weather starts this year. So I saw a few different mechanics who diagnosed the issue differently. First I tried to evacuate and recharge the freon. That didn’t work. So last week I paid $1200 and replaced the compressor.

The weather wasn’t too hot until today and I noticed that the same problem is happening again. I also notice that when the temperature cools off a bit (to about 75 or below), the AC consistently blows cold air. Obviously, I would prefer for the AC to blow cold air when its hot outside, no matter how fast I’m driving as it does when its cooler outside.

The AC is clearly capable of generating cold air, but does anyone have any idea why it refuses to do so when its hot outside? Is there some kind of temperature sensor in the system that may be defective? I want to have some idea of what may be going on before I take the car back to the place that replaced the compressor.

Thanks in advance for any advice.

It sounds like your electric fan or fans might not be working. It is only when you are moving fast enough for air to go through the radiator and condenser that you get any cooling.

It’s difficult to make much of a guess on A/C problems without knowing the high and low side pressures, what engine RPM those pressures are at, etc.

An A/C system working properly should produce dashboard outlet air temperatures at least 50 degrees colder than the outside ambient temperature.
Maybe the outlet air on a 75 degree day is really not as cold as you perceive it to be.

Agreed that you should make sure the radiator cooling fans are working when the A/C is on and the compressor is engaged. Inoperative fans cause the head pressure to rise too much which means more heat, etc.

Thanks for the replies.

I don’t know the pressures or RPM, but I have seen the condensor fan turning. I’m not sure if that means it is working properly or if there are other fans that should be turning.

Maybe I’m perceiving the system to be cooler at lower temperatures, but it’s definitely blowing warm (sometimes hot) air when the temperature is higher.

But shouldn’t they have checked the pressures before giving the car back to me? The guy said that they idled the car with the AC on for 40 minutes and it was blowing ice cold air, however, that was a cooler day in the 70’s.

I want to have some idea of what may be going on before I take the car back to the place that replaced the compressor.

What kind of place replaced the compressor? Dealer, A/C shop, Quick Lube place, trusted independent mechanic?

It was an independent repair shop that I want to say is a trustworthy place. I went there based on reviews from the mechanics files on this site.