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G20 Van R4 and 400 psi

sdr on Tue June 01, 2010 10:20 AM User is offline

Year: 1989
Make: Chevrolet
Model: G20
Engine Size: 5.7
Refrigerant Type: R12

The original R4 compressor was working last summer. This season it leaked around the body seals and was replaced with a new AC Delco unit. The accumulator and white OT were also replaced. The evaporator was cleaned using mineral spirits and shop air. The original white OT was coated black but it wiped off easily. There was one very small sliver of aluminum in the screen. There was no significant debri in the oil drained from the original compressor.

With the new parts installed, the system was filled with nitrogen to 70 psi to check for leaks. It sat that way for almost a week due to time constraints. Then it was evacuated for 45 minutes and recharged. It is clear that a better weighing scale would have been helpful in the recharge. The manual calls for 2 lb 12 oz and it is close. The temperatures of the evaporator inlet and outlet tubes were used to tune the final amount.

The next day it was re-checked starting with the engine completely cold. Before startup the static pressure in the system was 77 psi and the ambient air was 78F. Inside the van, the air temp was 80F. The doors were open, the fan switch on high and A/C set to normal. At startup with the engine idling, the compressor clutch would engage for about 7 seconds and then disengage due to the low pressure switch. The low side was 24 psi and the high side was 110 psi. After about 6 minutes, the compressor ran constantly and the low side was 30 and the high side was 175. After 12 mins, it was 34/205. A box fan was placed in front of the condensor and the pressures went to 32/175. The pressures continued to rise until they were 34/200. Removing the box fan they went to 40/230. After 20 min, the engine cooling fan clutch still had not engaged. The engine RPM was increased slighty above idle and the pressures went to 46/350 quickly. Increased the RPM again and the pressure on the high side was 400. Water was sprayed on the condensor which lowered the pressures enough to cycle the compressor clutch. The box fan was added again and the pressures stabilized at 40/300. Finally, the cooling clutch fan engaged and the pressures stabilized at 33/245. The engine temp gauge showed 140F (the mark between 100F and 180F). Continued to monitor this for another 20 minutes. At the higher RPM, and with the cooling fan clutch engaged, the pressures stabilized at 38/260. The ambient air temp in front of the condensor was now about 108F (from 78F initially). The air exiting the fan shroud at the top was 170F. Inside the right vent temp was 63F and the ambient in the van was up to 90F (from 80F). Measuring the temps of the evap. inlet and outlet was difficult because it was so hot. But they appeared to be 56/61F. The 56F reading was just below the OT. Hopefully this is not too much info, but aside from the clutch fan taking a long time to engage does this seem like "normal" operation? Should the fan be pulling more air with the fan clutch disengaged?

Based on the postings on this site, fan clutches tend to be a problem. This is the original fan clutch but it shows none of the obvious signs of being bad. No leaks, doesn't wobble, doesn't spin freely even when hot. Also, this van has has always been cold natured. For some reason, the hoses to the heater core bypass the engine thermostat. One hose runs from the back of the intake manifold to the heater core inlet. The heater core outlet hose is routed directly to the radiator. There is no heater control valve. This was changed for the next model year (1990). Once the engine heats up, the fan clutch does engage, but with the heater core bypassing the t'stat, it just takes a long time to get the engine up to temp. Are there any solutions to blocking the flow to the heater core until the engine comes up to temp?
Thanks for your help.

GM Tech on Tue June 01, 2010 11:40 AM User is offline

Condensers need air immediately-- put a new clutch fan on it-- you proved it to yourself by the box fan method....

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

bohica2xo on Tue June 01, 2010 12:50 PM User is offline

That fan clutch was dead a decade ago. Replace it.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

sdr on Thu June 17, 2010 10:02 AM User is offline

Thanks GMTech and Bohica. Installed a new AC Delco fan clutch (for 3.73 gear and reverse rotation) and it works much better. The fan doesn't sound any different but the airflow is definitely improved. The pressures stabilize between 40/255 psi and 42/275 psi with 90 F ambient at fast idle. Vent temp was 63F.

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