Hi everyone. This is my first post on here. I have a big a/c problem on my car. I have a 1999 Honda Civic EX coupe. It has 89000 miles. The a/c compressor was recently changed because it went bad. The drier was also replaced. When the a/c is off, the car runs perfect. The minute the a/c is turned on, the car starts to hesistate and pulse every once in a while. A friend told me it was the a/c compressor turning on and off, and so he was right. Now another thing, when the a/c is on, and the car is stopped at a red light or whatever, the idle goes up and down. Not alot, only sometimes, but it only happens when the a/c is on. The idle only jumps from 400-1100. Another thing, when the a/c is on, the idle sometimes goes very low, seems like its about to stall. There is enough freeon in the system, so its not low pressure. Does anyone have any idea what it could be. I have not taken it to the mechanics because all they do is tell you all sorts of problems that are not even the problems and you end up having to pay alot. Remember this problem only happens when the a/c is on. Also if i am at a red light, and i accelerate to about 2800RPM or 3000RPM and release the gas and let it go back down the compressor turns on and off. Same thing as if i'm driving. The compressor is brand new....its actually the second brand new one because i was having this problem with the other one, but its not the compressor. Please help....its really hot in Miami! Thank you guys!


Chris

 

Does the condenser fan work? The condenser is the radiator-like unit under the hood that is connected to the compressor. Its fan should be on all the time the compressor is engaged. Does the A/C get cold when you're driving? Are you sure it is not overcharged with refrigerant ("freon")? Overcharging or an inoperative fan will cause excessive pressure which will make the compressor cycle on and off rapidly.

If the A/C system is normal, the problem is just related to the engine idle controls, like the idle air control valve or EACV. Should the engine rpm go abnormally low, below about 400 rpm, the ECU will turn off the compressor to reduce the load on the engine and hopefully prevent completely stalling out. Then when the engine recovers it will re-engage.

 

Hey thanks alot. YEs the condensor fan is always on as long as the air is on. So the fan is working correctly. Now about there being too much refrigerant, im 99.9% sure its not that, because the pressure was at about 36 which is the normal pressure for the low side, so that cant be it. About the idle air control valve or eacv, it might be that, but the thing is, that as long as the air is off, the idle is perfect. The rpms are perfectly normal. When the air is off, and the car is at idle, the rpms are at about 700 which is pretty normal, but as soon as i turn the air on and start driving the compressor begins to turn on and off, and the rpms go up and down, but the whole idle thing happens sometimes. Why doesnt it happen when the air is off??? So you think is the idle air control valve, or eacv. Thanks alot, Chris

 

The EACV does not affect anything except at idle. If it's cutting on and off while driving it's probably doing that because of too much high side pressure. This could be due to too much refrigerant or air in the refrigerant system. You need to be able to measure both pressures to properly diagnose a problem like this. The high side tells a lot more about how much refrigerant you have than the low side, but charging by pressure is an inexact science in the first place. If you have been adding R134a but you don't know how much exactly is in there now, I'd suggest removing all the refrigerant and air (down to a full vacuum) and putting back the specified amount by weight shown on the sticker under the hood.

 

ok. Yes, i think it is that the high pressure is too high, because when we did the vacuum and added refrigerant the first time, the high pressure gauge was reading way too high, but we added the correct amount of refrigerant. So it has to be something else. and still, why does the idle go up and down, but ONLY when the air is on??? About the high pressure side, someone told me it could be the expansion valve, and someone else told me that it cant be that, but that it could be the high pressure switch on the drier. What do you think about all this?

 

What is your high side and low side pressure in psi? Also when you do that test take note of the air temperature outside the car.

The switch should not cut out until about 450 psi. If it is cutting out before then it is a defective switch. The expansion valve is unlikely to cause this problem. Excessive pressure typically results from inadequate cooling of the condenser, too much refrigerant, air in the refrigerant lines.

Running excessive high side pressure causes the compressor to be hard to turn, putting an excessive strain on the engine which can come close to stalling it at idle. Also the ECU is not expecting the pressure switch to be turning on and off (in normal operation, it is always on) so it doesn't compensate the idle very well when that happens. In other words the uneven idle with the A/C on is being caused by the A/C problem.

 

I have the same problem with my '97. At first I thought it was because the condenser fan wasn't coming on, but I fixed that (improved the problem) but it didn't go away completely. I guess I'll check the high side pressure and also the pressure switch. Thanks for the helpful hints mk378!

 

hey, well you wont believe it. IT fixed itself, just out of nowhere, lol. Yesterday, i went to check the idle air control valve. I turned on the car, and disconnected the plug from the valve to see if it was working. I reconnected it, and turned off my car. A few minute later, i went to turn on my car, because i was going to go out. As am driving, i turn on the air, and the compressor was not turning on and off. IT was so weird but yet, made me so happy. I took it to my friends house so he can put the scanner and erase the code that i caused by disconnecting the plug from the valve. He rescanned it, and no codes showed up, except for a dumb oxygen sensor. Now my a/c works perfectly, my baby is back to normal, and everything is fine. It is so weird, i wonder what happened. WEll i just wanted to say thanks for all the help you have given me, i really appreciate it.

 

I had the compressor cutting off and on and shade-tree mechanic put guages on it and the high side was 400. Said I needed a compressor and all the others. I said compressor seemed to be working if it was up to 400 psi . Investigated throught the forum and tried suggestions. Previous owner had a new condensor fan put on and I guess they charged the system also. It would almost bogg the car down at idle. As my thread from 5/13 shows I have at least a fix for now.ro


Thanks to all,
I got the Civic back from shop. They evacuated the a/c system said it was almost 1 pound overfilled. They recharged it with the proper amount and said it was cooling ok. Nice cool ride back from the shop. I will try it and see how it does when it really gets hot here. It is only 75 today. A/c did not act up when I bought it till temp got hot here.
Thanks again