1990 Pontiac 6000 V6 not cooling well

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UP_4012
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1990 Pontiac 6000 V6 not cooling well

Post by UP_4012 »

Good day, I acquired a rather good condition Pontiac 6000 wagon for $500 and decided to retro-mod it and make it my daily.
Rebuilt front suspension, transmission, steering, engine reseal and the whole works. I reworked the A/C system including a new V5 compressor, GPD part # 6511365 containing new PAG 46 oil (7oz). New evaporator, new liquid line, new manifold hoses, new accumulator, and all new schrader valves.
Condenser has been replaced with a Spectra parallel flow unit, and has two 10 inch fans on it for better cooling.
The blower motor was replaced with the evaporator and I used 3M strip-caulk to re-seal the case to the HVAC module and to seal off the gaps between he evaporator case and the refrigerant lines.
I have had bad luck in the past with GM compressor mounted switches, so I relocated the low cutout to the accumulator (27 PSI off, 44 PSI on).
I used a Ford blue orifice tube, 0.067 I think because the general consensus seems to be to use that for 134a retrofits.
This system is like a GMT400 with the goofy condenser mount orifice tube.

System has a factory fill of 44oz R-12, I charged 36oz R-134a.

System will not pull down much more than 10 degrees full fan outside air, and seems to be not able to get below 58F when at full fan recirc. At lower fan speed, the temps do get lower, as low as 49 when at fan speed 3 recirc at road speed.

I think I did something wrong, so I purchased a 2 channel K- type probe thermometer and attached the probes using zip ties at the condenser outlet and evaporator outlet to get superheat and subcool measurements.

At idle, full fan outside air, the system pressures are 56 low, 226 high, and if I did the math right, that makes superheat of 11 degrees, which is too low to my knowledge, and a subcool of 30, which seems to be very high.

I assumed it was overcharged, so I paid to have the refrigerant recovered ($100) and then charged in 30oz.

The results were 52 low, 220 high, superheat of 12.3, subcool of 28. Vent temps went up as well to 70F. :shock:

Before I buy anything else, and pay to recover again, I know I am missing something. I just don't know what that is.
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JohnHere
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Re: 1990 Pontiac 6000 V6 not cooling well

Post by JohnHere »

Currently, at only 30 ounces (is that *net weight*?), the system appears to be about 30-percent undercharged.

Not sure about your choice of OT's. If Carguychris85 notices this thread, perhaps he'll offer suggestions.

Superheat and subcool measurements are typically used in residential and commercial HVAC systems and are not used in MVAC systems.
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UP_4012
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Joined: Thu Aug 21, 2025 4:35 pm

Re: 1990 Pontiac 6000 V6 not cooling well

Post by UP_4012 »

Oh, OK. I guess I did all that for not much result. I used the formula R-12 charge * 0.9 - 0.25lbs then convert to ounces.

Yes, the charge is by weight from a scale I borrowed and a 30-lb cylinder I bought.

It was not clear to me if that orifice advice would only apply to fixed displacement vs variable in my case. I still have a spare Delco white tube just in case.
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JohnHere
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Re: 1990 Pontiac 6000 V6 not cooling well

Post by JohnHere »

The 52 PSI reading on the low side translates to an evaporator temperature of about 55°F. By the time the air passing over the evaporator gets into the cabin, it will be warmer than that, which explains the little to no cooling that you're experiencing.

You'll need to get the refrigerant charge amount to the optimum point and the low-side pressure down to about 28-32 PSI. How to optimally charge R-12 to R-134a conversions has been discussed a number of times on this Forum.
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