Got A/C working, but wont kick on at idle, only around 1500rpms+
 

1. So have A/C working again after motor swap(1999 GMC Sierra 1500 rcsb orignally 5.3, now cammed lq9)

The problem was the high pressure switch connector on back of compressor. The prongs got bent down when I first installed that connector back. Bent the prongs back correctly and reconnected it.

Now A/C works, but wont kick on at idle, only around 1500rpms+.

From everything I read previously this is a tell tale sign of low freon.

But I brought the truck to a mechanic I know and he said it is usually the opposite (low freon works at idle, but cycles clutch at higher rpms).

So I'm trying to find out what to do from here.

He used his Snap On scanner and said everything shows working fine, it just kicks the compressor on for 1ms and turns it right back off at idle.

He checked pressures etc. and said all was fine.

I'm still leaning towards low freon, what else could it be?

2. One other thing, my air recirculation actuator had been brocken for a while before doing motor swap because the gears were stripped and just clicking.

I replaced that actuator and now it will open and close that door, but gets to its end and just keeps clicking.

When I first installed it, it worked fine, then 15 minutes into use it just started clicking with no change in recirculation button.

I've tried the actuator relearn procedure without a scanner, where you pull a fuse for 10 seconds then start the vehicle and it is supposed to redo the learn but it didn't work.

How do I get this to stop? Or is it something wrong with my HVAC controller not seeing it correctly, and maybe it broke the original because something is going out on it, since its doing the same to a new one?

Thank you

Come on guys, could use some help

Sounds like a tune error to me. If it is really kicking on at 1500RPM, then someone did some funky tuning as the PCM is all that controls the compressor via RPM. The PCM will override any settings on the interior controls regarding the compressor.

Alternatively it could be exceedingly high head pressure due to a clogged condenser. Moving more air would drop that pressure. Plug in a gauge set and see what the readings are when the compressor is off vs. the compressor on.

As far as actuator relearn, I generally set the Recirc to on, then sweep the mode knob from left to right to left a few times. If it still doesn't work you could have a faulty control head.

Yep, need to know your pressures at idle and at 1500 RPM before we can diagnose much. Does your idle RPM drop when the compressor kicks on?

Well I am using EFI Live to tune the truck and I believe im still using the same settings as before the motor swap but can check to be sure. If it was in the tune where do I need to look?

its a 2001 PCM in a 1999 truck/harness.

I don't have a gauge set, but the mechanic did and used it and said everything looked completely normal based on pressures and freon level, other than the fact that the compressor clutch was told to kick on and would instantly kick back off at idle. Above about 1500rpms it worked completely fine also according to him pressure wise etc.

Idle RPM doesn't really drop, but the computer and cam have to sync back up because of the added strain at idle. But once it "catches its breath" per se it is same idle as without a/c on, just pulling in more air to compensate.


Every now and then it will work long enough at idle to give cold air for a few seconds, but is only once per start up max and rarely even does that.

There's a setting in the tune that turns off the compressor if your idle RPM drops below a certain level. I forget what it's called, maybe Stall Saver? Anyway, if your idle RPM drops for an instant when the compressor kicks on, then comes back up, the computer is probably turning it off to keep the engine from stalling. Most likely your idle airflow tables need some work to keep it from dipping when the compressor kicks on.

Yep that was it it.

Thought I was helping the truck by helping the stall saver kick in easier before I got it idling decent, but had no idea that effected a/c.

Thanks a BUNCH!!