My 2005 Jimmy's A/C works great except at low speeds.

Yesterday I started the engine and turned on the A/C, then looked under the hood to try to identify the problem. At idle, the A/C comes on when the part marked by a large black dot in the attached photo spins; as soon as the part stops spinning the A/C goes off. The face is loose when touched lightly by hand.

Does this mean a new compressor kit is required, or is there an easier fix to make this A/C more reliable?

TIA,

quickcurrent

 

That is the compressor clutch. When it engages does the compressor turn reliably and what is the center vent temp (get a cheap AC dial thermometer from the parts store)? Is that temp different between idle and cruising speed? It is normal for the clutch to cycle on and off so that does not tell you much.

George

 

Thanks GeorgeLG.

Yes, the compressor seems to turn reliably when it does turn. I was told by the dealer when the vehicle was nearly new that the rather loud off-on cycling was normal, but given the lack of A/C reliability lately, I was starting to wonder if I had been fed a bunch of bull, and the unit was defective from the beginning and was just wearing out very slowly! But, if that is indeed normal, then that is of no value. Should the clutch feel loose when pressed on slightly or taught?

I will check the temps and provide that feedback as soon as I have it. My son drives the vehicle and he has his own place, so I won't be able to get that until the next time a I see him, about a week or so.

 

The clutch is somewhat loose when not engaged. The vent temps will tell us of the refrigerant circuit is in good shape when engaged. If it is but it won't cool the cabin because the clutch does not stay engaged enough then we can go from there. We can jumper the clutch relay and make it stay on continuously for instance.

George

 

Anybody bother to check the fluid level?

 

I agree with newguy. A low charge of refrigerant will cause the system to short cycle.

 

Yes, low refrigerant charge can cause a system to cycle. At rest the system pressures are equalized on either side of the expansion device and as the compressor runs, the low side start to drop. If the charge is low, the low side pressure can drop below the low side cutoff pressure switch and disengage the compressor. That is however not the only reason for a malfunctioning AC system and adding refrigerent to a fully charge system can cause damage or at least crappy performance. Also, most of the cans of 134a that you find in the stores have no low side gauge or a lousy low side gauge as well as leak sealant in the charge which can cause its own problems. Vent temperature is a staple of proper AC diagnosis (and cheap) and I assume that the OP does not have a set of 134a gauges with quick disconnect couplers but the desire to do some diagnosis on his own.

George

 

My truck does this every spring, with the guage that comes with the 134 I top it of and it works fine all summer

 

This is certainly one approach and might work. If the OP has for instance a restricted metering device however, adding charge waiting for the low side to hit a certain target can be disasterous. Also, in the case of a system that leaks continuously, finding and repairing the leak is better. Sometimes its as simple as a $0.05 schrader core as was the case with my last repair which has held for 5 years and counting.

George

 

Great info guys, I was reading the other day about some guy who added refrigerant and once he did, he had too much in his system and the A/C started shutting off a low speeds and coming back on at higher speeds, exactly what mine is doing now, but for obviously different reasons. I have not added any refrigerant, so mine could, in fact, be low if it's leaking somewhere. But, if it's leaking refrigerant, I suppose I have a bigger problem, huh?