Automotive Air Conditioning Information Forum

I have a 1975 GMC pickup with a hybrid system (old and new components) and I've just evacuated and charged it. The temps look good, but since I can't really follow the OEM recommendations for R-134a, I'd like some feedback on pressures and whether I need to tune the R134a charge. Original R-12 charge was 3 lbs, 12 oz (60 oz), so I decided to use 44-45 oz of R-134a, based on a recommendation to use about 75% of the R-12 charge.

Readings today
Initial vent/ambient temp - 90 degrees
Vehicle: 1975 GMC pickup, SBC 350 with mechanical HD mechanical clutch fan and shroud, large parallel flow condenser, new Ford blue orifice, Sanden compressor & accumulator

After charging with 44-45 oz these were the readings:
At idle
Vent temp 45-48 degrees, high pressure 35 psi, low 150 psi
At 1500 rpm
Vent temp 40, low pressure 25 psi, high 185 psi

The vent temps got down to the 40's with about 36 oz of refrigerant in the system, and very slowly improved as I added the last 4-8 oz.

All the pressures are lower than I expected, but the vent temps are great. Should I try adding more R-134a, or just stick with my plan for 44-45 oz?

Thanks,

Bruce

Personally, if it worked good for me, I'd leave it as is.

"Never trouble trouble until trouble troubles you" - Yogi Berra or someone else...

I have the same feeling - just leave it as it is and wait to see how it works. Its an old single cab truck, so 40-45 degree air cools it down fairly quickly. All the vents are flowing well, but I do need to verify that the vacuum doors for the max/recirculate setting are working properly.

Another question - The recommendation in the Sanden instructions was to use a 17 series V-belt (17/32" wide); however, my stock crankshaft pulley is designed for a 15 series V-belt (15/32" wide) so I used the narrower belt. I assumed that the wide belt might ride up and out of the narrower grooves in the stock pulley. Is there any real advantage to using the slightly wider belt with the Sanden?

Thanks,

Bruce

bcarlson78248 wrote:Another question - The recommendation in the Sanden instructions was to use a 17 series V-belt (17/32" wide); however, my stock crankshaft pulley is designed for a 15 series V-belt (15/32" wide) so I used the narrower belt. I assumed that the wide belt might ride up and out of the narrower grooves in the stock pulley.
Bruce

Bruce - I'd keep the narrower belt on there for now. see below:

Cusser wrote:Personally, if it worked good for me, I'd leave it as is.

"Never trouble trouble until trouble troubles you" - Yogi Berra or someone else...