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Old 03-02-2007, 03:41 PM
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A/C cycles, 3lbs installed

Maybe some of A/C guys knows what is going on.

Problem: Compressor cycles

Vehicle: 93 Chevrolet Caprice 305 engine R-4 compressor. system holds 3.12 lbs of R-12.

What has been done:
(Converted system to R-134a)
New (not rebuilt) R-4 Compressor
New Drier
New Orifice
New Hoses
All new O rings
Reverse flushed Condenser and Evaporator

Install procedure:
Removed all old equipment and put a/c flush in Evaporator and Condenser. (let sit while I got everything else ready to install)
Pour shipping oil out of new compressor.
Poured 4 oz of Ester oil in new compressor and rotated compressor 10 revolutions and poured oil out.
Poured 4 oz more of Ester oil in new compressor and rotated.
Poured out all the oil and put in 7oz of new Ester oil and capped compressor.

Flushed out Evaporator and Condenser with dry air line at 60 psi. Then allowed remainder of flush to evaporate out.

Connected new hoses with new O rings lubricated with clean Ester Oil.
Installed New Compressor, connected high and low side hoses.
Rotated compressor by hand (socket and rachet) for 10 revolutions.
Connected guages and pulled 27 inches of vacuum for 45 minutes and then disconnected vacuum.
Let the system set over night (19 hours) on the guages.
Next morning, still holding 27 inches of vacuum.

Rotated compressor a few turns and began installing first can of R134a. Engine not running at this point. After about 1/2 can 6.5 oz of 134a I started engine and turned on a/c to Max with high fan speed.

Just as the first 13 oz of 134a started to empty, the compressor started cycling.

At the end of 26 oz of R-134a the compressor continued to cycle.
Low side pressure would increase to approx 40 then the compressor would come on. When the low side decreased to 25 the compressor would shut down. On the high pressure guage the reading would hover at 50 lbs.

At the end of each cycle, as the guage would drop to 25 the compressor would start knocking and then shut down. Once the pressure on the low side would climb back to 40, the compressor would come on and run quiet. But again the low side would drop to 25 and start knocking again.

Now I have 3 cans (39 oz) of R-134a in the system and it still does the same thing. High side reads 50 lbs, low side goes as high as 40 and as low as 25.

Any ideas?
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