lucas287

iTrader: (1)

Turn AC on...compressor kicks on about ten seconds later. While still at idle the compressor stays engaged, hardly cycles. Touch the throttle, bring it up to 1000 RPM and the compressor begins to cycle on and off.

So what I have noticed is warmer vent temperatures correlated to higher engine speed.

Nothing too dramatic, just slightly concerning.

At idle, parked, vent temps of 42*, highway about 52*. Ambient=85*

Any ideas? I do not have a manifold gauge set, im thinking that is my next reasonable move? That way I can see what is going in with my pressures.

Roughly about 20 thousands air gap on the clutch btw.

MikeGyver

iTrader: (5)

Skip to the last line for your answer.

Changing the rpm of a compressor changes its capacity. At idle, it might be 5000 BTU. At full capacity, which might be 2000 engine rpm, could be 48,000 BTU.
You are describing exactly how a system acts when low on freeze gas. There is enough freezon for low capacity, but when you rev it up, the compressor is disabled by the low pressure cut out switch.
Because r134a is a two-part gas, when it leaks out the ingredients left are in an incorrect ratio (one component evaporates more slowly).
Every time you add gas, you compound the problem. When you just top off the charge every year, eventually you will have poor cooling even with a full charge. The only correct way to charge an r134a system is to pull a vacuum and weigh-in a fresh charge.
You need a vacuum pump and a refrigerant scale to do it properly.

You are low on gas.

lucas287

iTrader: (1)

Over a year since you made this suggestion! this past weekend i installed a new (used) compressor, accumulator, orifice tube, and all new seals. I pulled a vacuum for three hours then charged with approximately 29 oz.. High and low side pressures are within spec for temp and humidity. Vent temp in 95* ambient is a constant 40* no matter the speed/rpm.

Here is my concern: i cannot audibly tell the compressor is cycling. While reading pressures i brought engine RPM to 1500 and the pressure dropped, but never to 30 psi (which trips the low pressure switch).

Does this sound alarming in any way? I am used to hearing the compressor click on/off randomly. Cannot say that i have heard it do this AT ALL while the AC button is on.

2000 Silverado 4.8

lucas287

iTrader: (1)

Correction to above, i am noticing now that the compressor is cycling. I was so used to having a worn compressor and low on gas. Drivers side vent temp is still holding steady @ 40* even in 95* ambient.