I have a 2001 SL2 with about 98K miles, and am starting to have some problems with it. Specifically, speaking...

At idle, the A/C blows hot, once i get moving it gets cold, ice cold.
The radiator / condenser fan is chugging along exactly as it is supposed to, and the engine is running on the lowish side of the normal range... (sorry, no specific #s to give...).

I notice the compressor is not kicking on at idle speeds, but once I kick the RPM up a bit, it kicks in...

I am thinking low refridgerant, however I have no manifold gauges to prove or disprove that.

Mind you, I WAS at one time, a VERY long time ago auto A/C certified, but have been doing I.T. work now since the early 90s, so to say my auto skills are rusty is a bit of an understatement... What else would cause the compressor clutch to not engage at low rpm, but engage at higher?

 

I'm thinking a weak A/C clutch, or perhaps a low-voltage condition at idle, but you didn't mention flickering lights ... Make sure your A/C controls are set to maximum (recirc) and put a voltmeter on your battery. You might not be getting everything out of your alternator at idle speeds

 

I am a native Oregonian living in Coastal Texas, trust me, the thing runs full speed recirc 24x7 9 months out of the year.

Not sure how to test for a weak compressor clutch.

No light flickering, and the load test shows no problems with the charging system.

I've got my truck to drive to work...

 

Having attended college at the University of Portland on the banks of the Willamette River many years ago, I can understand your distress of our "southern heat".

Stop by your local AutoZone (or similar such), and rent/borrow a set of gauges. Need to get the pressures (hi and low) both when stopped, and when running. Might be a trinary switch problem ...

 

Heading up to Harbor Freight to grab a manifold gauge. To give you an idea how long it's been, my existing manifold gauges are R12 gauges... I know I can get the adapter couplers, but those things cost nearly as much as gauges, and my old ones were getting nasty when I quit using them years ago. I just need to toss them out.

Not familiar with what a trinary switch is. Is that the same as the pressure switch? I need to dig back into the manual, but I don't see any reference to a trinary switch, or a pressure switch of any sort, but I would expect there to be a low pressure switch to keep the clutch from engaging at all with low freon levels...

Man I hate being this rusty on skills that used to come without thinking... Getting older sucks.

 

A trinary switch is just a that, a device that opens (stops) the compressor if the pressure falls too low, or if it rises too high. After sleeping on your problem, I'm leaning more to the possibility that your expansion valve has gotten contaminated, and is not operating properly. This would allow the pressure to rise too high at idle, and trip the compressor off. As the car starts back up, the additional cool air over the condenser coil would drop the pressure, and allow the compressor to restart.

 

Your thought process is along where I am thinkign, but the thought bugs me...

If the system is closed, how could the expansion valve get contaminated?,

Mind you, lack of pressure data, caused by lack of manifold gauges isn't helping the diagnosis at all... The HF gauges were a bust. And the ones at Autozone are worse...

Just got a text back from a friend, might have to swing by his place and borrow his gauges. Looks like I may have to vacuum down the system...

Is recovery of R134a required yet?

 

Weelll, yes ... but unless you have a government man standing right there when you break into the system, I seriously doubt if anyone will be the wiser (except for you). Heck, some shops will even suck it out for you at no charge -- all you gotta do, is find one ...

 

New wrinkle. The thing overheated at the JIB drive through last night. Looking like it may have a fan issue. But the fan was replaced with a new AC Delco fan motor less than a year ago...

 

Some fans fail by only running at half-speed or less ... dunno if the bearing is bad or what