A/C will not go below 60 degrees and does not cycle?

SANFORD1970

MEMBER
1970 CHEVROLET TRUCK
5.7L
V8
2WD
AUTOMATIC
4,000 MILES

Hello, I have a Classic Auto Air A/C system that I installed in my 1970 C10 around 12 years ago. (https://www.classicautoair.com/shop/complete-ac-systems/1970-chevy-pickup-truck-air-conditioning-system/). I am having trouble finding the source of an issue that keeps it from getting cold. (Below 60) The system has a new compressor and drier and holds both vacuum and pressure. The manual says to charge with 24oz of 134a and pressures should be 10-25 on the low side and 150-274 on the high. I'm at 22 on the low and around 210 on the high. The air temperature outside is around 100 degrees.

The compressor used to cycle on and off and now it does not. I have a low side pressure switch that is functioning, and the clutch did not engage until the first can of 134a was being introduced. The is no high side switch and I believe the cycling is controlled by the expansion valve? And I also suspect this might be the issue.

So, before I start the long task of getting the box out, I wanted to get some expert advice of what's left to trouble shoot. Thanks in advance.

5 Replies

KEN L

MASTER CERTIFIED MECHANIC
47,512 POSTS

At 100 degrees the high side should be at about 250 PSI. Please add more refrigerant and let me know what happens.

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Saturday, August 19th, 2023 AT 10:51 AM

SANFORD1970

MEMBER
3 POSTS

Thanks Ken. I had around 11oz in a can, so I hooked it up. Gauges were steady at 17/195 and blowing 61f before I opened it up. Still 100f outside. And again, this was at the 24oz of charge the manual stated.

It drank up the 11oz and now the pressures have settled to 19/225 and is blowing 45-48f

Incidentally, this aftermarket system has a cable operated valve for the heater flow. I removed one side to make sure it was not leaking and it did not appear to be. But I clamped it off on the positive flow side to the heater box and it dropped 5 degrees. (45f) I removed the clamp, and it went up to 50-51f. Reinstalled the clamp and back to 45f.

So, I have a few questions:
1. Is it okay to have more refrigerant in this system than the manual says to?
2. Does 45-48f seem close enough? That is almost a 20-degree drop.
3. Is it normal for a heater hose to have an effect on the A/C? I know the two exchangers are close and mine is obviously having an effect. I will leave it clamped off until the summer is over.

Thanks for your help!