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Hello all,

My mom has a '99 Civic LX with an odd problem. At idle the AC works just fine and blows cold. Under any sort of load, even sitting in the garage just revving the engine, the compressor shuts off and won't come back on until the RPMs drop way back down (haven't notice a particular RPM, just low) or, if she's driving, it'll come back on when she's coming to a stop. Granted, the compressors can shut off under a heavy load but "only-On-when-not-moving" is not helpful in El Paso.

This one has me stumped as I don't even know what signal shuts of a compressor on a Civic. Vacuum? RPM? Any help would be greatly appreciated!

Thanks!

 
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Clutch might be worn out

 
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Nah, it's not slipping, it's actually shutting off (I can watch it). Plus the compressor is new.

 
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Cheap aftermarket compressor?

 
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How/why would that cause it to shut off with higher RPMs?

 
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Because it's a junk part. These cars are picky about certain things.
With the car sitting in the driveway, will the compressor disengage just from you stepping on the gas? Or does there have to be a load on the engine?

 
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Sorry, my question was bad. Exactly how would an aftermarket compressor disengage because of RPMs? I've worked on lots of AC systems, have replaced many compressors, even installed an AC system in a car that didn't have one at all but I've never come across this before. My thoughts are that it's getting an erroneous signal to shut off under RPM's but I've never worked on a Civic before so I was hoping that someone here has some insight into the command sequence that causes the compressor to shut off. Is it vacuum? Is it based off an RPM from the ECU? I don't know these cars.

Yes, the compressor will simply disengage from RPMs while in park, in the garage. Idling it's fine but as soon as the RPMs go up, it just disengages. While driving it also disengages but will re-engage when coming to a stop (stop sign, stop light, etc)

 
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Honda have long had the ELD to control alternator charging (reducing when engine is in high loads) but I do not think they had similar for AC, so that item can be checked off the list.

what is causing it... sorry don't know

 
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Not that I'm aware of, I've never had to do a deep dive into the AC system on a 6th gen before. Have you verified that the clutch relay is shutting off? The +12v or ground is no longer at the relay coil?

 
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I know this is an old thread but has there been any solution to this problem? I’m having the same exact issue.

 
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Have you tried/checked any of the things in the above posts? Any work done to the car recently?
Any other relevant info you should have put in your original post?

 
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Yes I’ve tried a few things.

I’ve switched the clutch relay with the condenser fan relay to see if the issue changed and it didn’t.

I’ve recently changed the compressor, evaporator, expansion valve , condenser coil , receiver and pressure switch

I’ve checked power to the compressor clutch (red wire) and I have power to it but once I give it any throttle I loose that power signal. I’ve jumped power straight from the battery to the plug coming out of the compressor and the compressor will run but obviously I’m bypassing a bunch of stuff.

I’m wonder if the temperature control inside the car has been know to fail or cause this issue?

 
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Next step would be monitor ECU compressor output and A/C pressure sensor.

 
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Thanks for the suggestion but I don't have a way of monitoring the ecu output. Sounds like I would need one of those fancy diagnostic tools. I guess I could try to figure out a way to check the control voltage going to the compressor clutch relay.

 
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The issue seems to be with the ground signal from the ECU. Instead of jumpering the +12V to the compressor, try jumpering the ground to the relay coil (ECU side, not the +12V side). Or, you could measure resistance to ground at this same point when the ECU calls for the compressor.