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

Tiny
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.
Friday, August 18th, 2023 AT 5:19 PM

5 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,144 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
Tiny
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!
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Saturday, August 19th, 2023 AT 12:01 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,144 POSTS
It is not okay to have too much refrigerant but the pressure tells you how the system is doing, it sounds like it is as cold as it's going to get, also you might want to keep the heater hoses blocked for the summer.
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+1
Sunday, August 20th, 2023 AT 11:12 AM
Tiny
SANFORD1970
  • MEMBER
  • 3 POSTS
So, I'm still having cooling issues. And it seems when my high side pressures are reading normal, my low side pressures are not. It was 110 and my high side was 350 PSI, but my low side was 29. My low side has been reading low all throughout this troubleshooting process.

Is this a symptom of a faulty expansion valve?
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Monday, August 28th, 2023 AT 5:25 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,144 POSTS
It sure sounds like it, or there is too much oil in the system.
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Tuesday, August 29th, 2023 AT 10:15 AM

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