A/C Idle Issues.

[therealsethallen]

So we've been graced with 82° heat today in Massachusetts. I've been running the A/C all day and it's only given me a few hints of trouble. It does blow cold air though not as amazing as I would like.


One, there's a horrible whine from the underside of the truck when the air is on, almost near the transfer case.

Two, when I shut the air off the first time at idle the truck nearly died, the oil pressure dipped, and the check gauges light came on. It seems to idle down when I lower the fan speed as well.

I'm completely clueless as to what could be going on here. Bad compressor perhaps? I'm stumped and I'm hot and bothered by this.

 

[Sparky]

First answer when cycling the AC causes engine RPM drop - clean the throttle body if it hasn't been done in a while. Oil pressure dipping is a result of low engine RPM (slow engine speed = slow oil pump = low oil PSI), so that's just a symptom of something else.

The AC compressor is down on the lower driver side of the engine, so, I could see if the AC compressor is making noise how it might sound like it is near the transfer case. Nothing about AC though is actually close to the transfer case itself however so you shouldn't be getting any AC-related noise from that area.

 

[therealsethallen]

See my thing is though, it doesn't idle bad with the A/C off or on. It idles smooth. It just jumps any time I shut the air off, throwing the truck into a near stall.

 

[Mounce]

Mine has acted up a few times, idling with ac on and random stumble, near dying a couple times. My figuring is probably throttle body, been about 20k since I've cleaned it.

Wouldn't be a bad first move cleaning it.

I've got an occasional rattle in a similar spot, narrowed it down to the rear ac lines vibrating together. I figure you don't have rear ac though.

 

[Sparky]

It is the load change that can cause the stumble with a dirty TB, not the consistent load (or lack of) at idle that can potentially throw it off. Just saying it is a starting point if you haven't recently cleaned it and it doesn't take much time, effort, or money to do as an easy starting point.

 

[therealsethallen]

It hasn't been cleaned this winter, I know. I've severely neglected this truck. It's due for another set of plugs, a new air filter and a thermostat in the next few days. I've just been wicked busy. Last time I cleaned it was the first weekend of November, at least. So it's likely time.

On the rattle, best thing I've been able to figure is that it's the manifold heat shield rattling, and it only seems to do it with the A/C on and cranked.

 

[webdawg]

Check the fan clutch.

Search this forum, their are really good threads on it. If I remember correctly, it engages when AC was on. Mine was toast.

 

[Mooseman]

What about when the compressor cycles on/off? If it's cool outside and you set the HVAC to low fan speed, the compressor should cycle on/off. If the idle is minimally affected, at least it's not the compressor.

Radiator Fan doesn't work quite that fast to affect idle as soon as you turn off the A/C. I've seen it using the Tech 2 to control it and it slowly ramps up and down the fan speed.

 

[therealsethallen]

My thoughts are the same on the fan clutch, it's way too slow moving. It doesn't seem to be as bad as it was last summer. Now it's only when it turns off.