Cold at idle, not when running at speed

[Cps38]

Specifics;
1974 DeTomaso Pantera. Replaced York with Sanden SD508 compressor, new expansion valve, filter drier. Vacuumed down. Charged with 2 lbs R12. Low side 25, high 125. Drove a little, cold at idle, went hot while driving. Went to add more R12, now low side 75 high side 130 at 88 degrees 50% relative humidity. Static and running pressures almost the same.

I’m lost understanding what’s going on. Once again, nice and cold at idle, completely gone over 2000 rpm. Compressor belt is tight.

[bohica2xo]

R12 charge. Wow, don't see that very often anymore.

How much oil did you put in the system? What type of oil did you use?

Properly charged at that ambient temperature I would have expected to see 200 to 220 on the high side, especially with the original Pantera condenser and fan assembly

[Cps38]

5 oz Ester. Yes, exactly. That’s what I would have expected.

[bohica2xo]

New dryer, was the rest of the system flushed?

[Cps38]

No.

[bohica2xo]

5 ounces of oil and 2lbs of refrigerant seems a little light for that system.

Long lines and slow oil return. An undercharge would reduce oil return even more. The old tecumseh had 14 ounces of oil in the crankcase.

How did you charge it?

Is this a genuine Sanden 508?

[Cps38]

Generic knock off, not genuine Sanden. Charged from 14oz cans from manifold gauges into charge ports on compressor. Added quantity drained from old compressor.

[bohica2xo]

So is this a replacement of a previous 508 clone?

I asked about the charge method because with R12 on that car it is good to use the sight glass. There are several sources with different charge weights.

I am assuming those are idle test pressures. How about the full load test:

Doors open, cabin fan on highest speed. Raise engine rpm to 1800 and keep it there for 90 seconds to stabilize. Record high and low side pressures while at 1800 rpm . Record ambient temperature and vent temperature.

[Cps38]

No, this replaced the original piston compressor. Sight glass went from foam to foggy/clear eventually. Those pressures stayed in that range under tests similar to your suggestion at 85 degrees 55% relative humidity. No vent readings per say, but very cold at idle to warm air under load.

[Cps38]

I’m starting to get the feeling the only way to correct this is to flush the system. Is it preferred to remove the expansion valve, disconnect the lines at the compressor and flush through the evaporator, condenser, filter/drier and not the compressor?