2000 Honda Civic EX Air Conditioning is driving me nuts!

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 50mph, 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 50mph.

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.

[losmaster]

You could check and see if it has a cabin air filter in it and replace it, if its dirty.....is the condenser electric cooling fan "running on high speed", with the ac on? I can't remember exactly what the set-up is on a civic, but doesn't it have 2 fans, up by the radiator? This might explain why it doesn't operate properly while sitting still, driving at slow speeds or its hot outdoors......if the high side pressure exceeds the pre-set limit....the pcm(cars computer) will cut the compressor off automatically.....when its cold outside or when driving at hwy speeds, you don't need that condenser fan to run......the high air flow keeps the rad./condenser cool and the high side pressure in normal operating range....check these things out, tell us what you find....then we'll go from there  

Thanks for the reply.

I was told that the cabin filter was checked a few weeks ago when I had some brake work done and I wasn't told that it needed to be changed, so I'm assuming that isn't the problem, but I'll try to have it checked again.

I have seen one condensor fan turning sporadically in the front, but I wouldn't be able to tell if it's functioning properly so I'll ask about that when I go back.

[discretesignals]

If you could, ask them what are the low and high side pressures reading when the air is blowing warm.

I had the same prob in the ac compresser sed to turn off durring idleing & only cool when the car ia above 50-60. The ac going off is bearable in cooler times in at high noon i guess its better with the windows down....Tried everything, checking the gas pressure, (High & Low side) opened the compresser, got another relay fitted, got the radiator cleaned cause i thought the car might be heating up even swaped the E.C.M. Sometimes the check engine light used to also turn on when the ac is going off-on. Gave up on the whole thing, recently i got the key turn on switch bypassed to make the car a push button start & all of a sudden the ac is as good as new. I think the old original switch had turned weak & was not giving enough current to the compresser. Hope this is of some use.