Hey guys. Something is going on with the AC in the truck. With the AC on and at the engine at idle it feels like the compressor will kick off and on momentarily. You can just feel it start to drag the engine down then it seems to let go. The truck always puts out cold air and doesn't have any problems when driving except periodically while idling. We checked the high and low side with gauges and it was fine. My friend suggested that the low pressure switch may be going bad. I couldn't really find anything suggesting signs/symptoms of a bad LP so any help would be appreciated. Thanks

 

I checked all the wiring to make sure everything was getting a good connection and it looks good. Any ideas?

 

Sounds more like the high pressure switch is cutting it out. If it operates normally while going down the road, it may be a temperature issue when sitting idle.

 

If the pressures are OK and the outside temp is 'moderate' (not too hot), it's normal for the compressor to cut in and out. The engine speed should be maintained about constant by the computer and the Idle Air Compensator Valve (IAC). If the IAC valve is sticking, the idle will be erratic, especially when the A/C is on.
Search for how to clean the IAC for your year.
Hope this helps.

 

Do you mean engine temp or outside temp? Engine rarely gets over 200. It has 2 electric fans on it. Outside temps are usually in the mid 90's here in FL. Almost the only time I notice it is when I'm picking the kids up from school because it sits and idles for 15 or 20 minutes while I'm sitting in line.

We checked the pressures and they were just slightly low- still within normal limits but we added a hair anyway just to make sure. Normally it's so hot here the compressor rarely comes on and off. I know what that normally feels like but this feels almost just like a miss and it's just momentary. It feels like the compressor is just beginning to kick on when it drags the engine down but then kicks off in a split second. It only happens when the AC is on and just started doing it one day out of the blue- it had been in the 90s here for a while before it started doing it. The idle is fine and smooth.

 

I meant the A/C system temperature; which if high enough would cause the high pressure cutout switch to open, cutting off the compressor.

 

Ok- something else it started doing is once the RPM's get a little over 2000 or so it stops blowing air- would that also point to the high pressure switch? Once the RPM's come down it blows cold air again. Does it have any kind of WOT sensor that shuts it off maybe kicking in too early?

 

I recall seeing something in other posts about this related to the compressor clutch air gap. You may want to use the search feature of this forum and see what comes up.

 

Initially my AC wasn't working properly because the air gap was wrong. That was fixed and everything was fine for a few months. Then it started doing all this. I left it idling in gear today for about 20 minutes with the AC on- shaking wires and what not to see if anything seemed to be shorting out but couldn't find anything. I noticed that the clutch never disengaged. Is it supposed to? Also the IAC and TPS sensors are new.

 

Depending on the outside temp and humidity, it would seem normal for the compressor to stay engaged while idling. The only way to really check this properly is to hook up some good gauges to the hi and low ports and see what the numbers are.