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A/C not cooling at idle.


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im posting because I am out of ideas. I am a transport refrigeration tech for a living, so i'd like to think Im halfway knowledgeable on a/c systems, but this one has me really stumped. my a/c has been flawless up until this summer. earlier in the year it started acting up, and I attributed it to the fact that up until about a month ago, my truck had a bad parasitic amp draw (aftermarket stereo) and I deleted the cats, and with that, I had a tech at a gm dealer give it a tune so I would not have a check engine light on and still pass emissions (which it does.)


the problem with that, is that when the battery is disconnected, the pcm has to relearn so it is very lopey at idle and just off idle for about a week. so lopey to the fact that it sounds like it has an insane cam in it, and you have to build rpm's on the brake coming up to a stop light and while parked. I assumed that the SS a/c system with the transducer and digital display had the ability to watch rpm, and turn off the clutch below a certain rpm threshold.


so now the truck is running well, but a/c clutch still does not engage until driving about 15mph give or take. I have been swamped at work, so I threw a clutch cycle switch on it to see if it would work. not only did it not work, I must have overtorqued the switch, because the plastic threads stripped, and leaked out all the refrigerant. ok, no big deal.


so I evacuate and recharge the system, and put the original switch back in (the one on the accumulator.) the condenser is perfectly clean, and pressures are optimal while someone holds the rpm's above 1500 or so. it still does not work at idle. it will occasionally, but not consistently as it should. I have a temp probe in the dash outlet, and on the highway it will put out air as low as 52 degrees. at idle the output is ambient.


I am very curious what the function of the 3 pin transducer is. if youre standing in front of the passenger side headlight and look down, you can see it on a line just above the compressor.


any thoughts?

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I'm not a/c expert, but you should be able to achieve an outlet temperature in the low 40's. 52 degrees is pretty high unless the outside ambient temps was over 100 degrees. I have a slow leak in my system and every spring I have to recharge it. I usually need to put in 1.5 lbs to get it fully functional again and have an output of 38F on a 85F day.

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I remember it being much better in the summers before this one. does anyone know of a location I could find specs and accurate wiring and troubleshooting materials for this truck? I remember being able to see my breath on humid days. I miss that LOL.

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The PCM controlls the compressor, so if you have a bad idle or low A/C pressure, it won't turn it on.





I'd suggest fixing your idle issue first, removing the cats should have no effect on it. Sounds like you might have a vacuum leak or bad spark plugs. The original spark gap for our trucks was soemthing like .055 but was later revised to .040.


I noticed a much smoother idle and better running when I replaced my fairly new .055 plugs with .040 plugs.

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