Hello all, I just joined this forum today and am in hopes that someone can tell me what I am doing wrong. My wife has 1995 GMC Suburban, 5.7 liter, TBI, that has the R4 compressor. I have replaced the compressor 3 or 4 times in the 18 plus years she has owned it. The truck has 237,000 miles and is mechanically sound except for the one accessory, the air conditioner.

I just installed a Harrison unit from a wrecked '95 Burb that was working when it met it demise. I installed a new condenser, accumulator, rear expansion valve and orifice tube up front. I flushed the lines. I had previously installed a new evaporator up front last month because it was leaking. I pulled a vacuum on it for 3 hours. Gauge went to -29.5 on low side, 0 on high side. Held a vacuum for an hour.

I put PAG 150 in the compressor and the accumulator.

Unit took a charge with no problems, ran fine and cooled for 2-3 days. Then the compressor started short cycling, the clutch was kicking in and out. Ran tests on clutch it read 3.68 on DM, which is in range. 12.24 volts to compressor. Thinking I may have added to much oil I took the compressor off and emptied it. Was only able to get between 1/4-3/8 an ounce. I did drain about 3.25 ounces from the accumulator. I had put 2 ounces in it if I remember correctly. Reinstalled the compressor along with another new accumulator. Added 1 ounce of oil to compressor, 1/2 ounce to accumulator. I had put 8 ounces in the compressor the first time, thinking the system held between 8-11 ounces and could handle up to 30% overage. Last compressor was bone dry thanks to leaking expansion valve in rear.

I have not been able to get the compressor to stop short cycling. It is better than it was after draining oil and I forgot to add I installed a new low pressure switch on the accumulator. (GM's have been notorious throughout for failing LPS.).

I do not have a recovery unit, but have gauges, scales (4.0 lbs put in), vacuum pump and a lifetime of mechanical work. This one has me about ready to throw the towel in. The compressor is strong and quiet when running.

At first when the clutch short cycled it caused the Burb to lurch. For some of the ole' schoolers it was as if the points were too wide. Turn AC off and it ran fine and will still sit you back in the seat.

A local mechanic friend ran a diagnostic with his OBD I tool and it showed mechanically everything was fine. He told me I made a bone-headed move and put too much oil in when I first installed the compressor. I did not get that much out, but I did not bust the rear unit loose due to it being a true PIB and the lines being seized underneath.

I enjoy keeping vehicles up and find it relaxing to still do mechanic work to give me a break from the occupation I am in. But, this air conditioner has about whipped me down.

Any ideas as to what to check?

Thank you,

WHMac
whmacauto@gmail.com