A/C in and out at high ambient temperatures

Tiny
NJBOLAND
  • MEMBER
  • 2004 CHEVROLET TRAILBLAZER
  • 4.2L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 125,000 MILES
Hello. Problem: A/C compressor will cut out when the ambient air temperature is high (above 75) and on highway for sustained period. I know that it cuts out because it will periodically come on again for a short period of time (few minutes) if I turn it off and let it rest for a few minutes. A/C seems fine around town and when the ambient temp is lower than 75.

What I have done: checked pressures with gauge set - charge at lower end of limit but it works; Orifice tube was changed end of last season (in Northeast US).

What I suspect: after reading your website: fan clutch bad, fan clutch relay possibly bad, maybe need to put in a little more refrigerant.

Edit: no codes and no overheating problem at all. Fan can be stopped without too much pressure on side by hand with a rag. It does not pull or thump when stopped and it does not seem to sound like a "jet engine".

Thank you for any help you can provide. Best regards!
Tuesday, June 23rd, 2020 AT 7:24 AM

7 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
Good afternoon.

What is the high and low side pressures while the engine is running? I need those pressures to help you with your issue.

This could be a freon issue and that is why I need to see the actual readings.

Roy
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Tuesday, June 23rd, 2020 AT 10:20 AM
Tiny
NJBOLAND
  • MEMBER
  • 5 POSTS
Thanks Roy!

Low side 25-28, high side 150. Ambient temperature 75 degrees in the shade. Static pressure 75-80. Have a better quality gauge set on order. Thanks again.
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Tuesday, June 23rd, 2020 AT 11:04 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
At 75 degrees, the high is low. The low side is within specs but I do not like the static pressure. Those reading should be exactly the same. That tells me you need an expansion valve.

The high side should be 2 times ambient plus 15%. The low side should be a steady pressure between 25-30 pounds.

Roy
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Tuesday, June 23rd, 2020 AT 11:11 AM
Tiny
NJBOLAND
  • MEMBER
  • 5 POSTS
Thanks. The static may be the same on both. I will take a reading when the new gauges arrive. The current ones are DIY special and not very detailed in scale. Will report back.
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Tuesday, June 23rd, 2020 AT 1:50 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
You are welcome.

Keep me updated so we can continue.

Always glad to help.

Roy
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Tuesday, June 23rd, 2020 AT 2:01 PM
Tiny
NJBOLAND
  • MEMBER
  • 5 POSTS
Hello again Roy,

New gauge set arrived. Ambient temperature at cold start this morning was 73 degrees, static pressures even at 70. Got back to it a bit later on, ambient up to 75 degrees, compressor not staying on so I added a can of 134a until the the compressor stayed on and I had a reading of 35 on low side. High side reading was 125 (both using the 134a scale not the regular psi scale) and the needle was fluttering. Can feel pulsing in the service valve connection on high side. This is low, based on your comments above. Compressor remained on.

Separate, but related question: Based on your thoughts about the expansion valve I did a little digging around for parts. Question, I know that this vehicle has a orifice tube filter because I changed it last summer. Does that mean it does not have an expansion valve? My understanding is that most vehicles have one or the other. There is an expansion valve available from NAPA or GM. This vehicle has rear A/C too. Not sure if that makes a difference, but with the rear A/C, it does take more refrigerant according to the label.

Should I put more 134a in? Using the 12 Oz cans or should I have it evacuated and start over again?

Thank you again for your help. Best, Nick
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Saturday, June 27th, 2020 AT 9:04 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
Okay, I would recover the Freon and start over by evacuating for 45 minutes and charge the exact amount.

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

The low side pressure should be 25-30 pounds rock solid. The fact the static pressures were equal tells me the expansion valve is good.

If the high side gauges flutter, the compressor is bad. It should never flutter at all. That indicates the reed valve is bad inside the compressor.

https://www.2carpros.com/articles/replace-air-conditioner-compressor

Roy
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Sunday, June 28th, 2020 AT 4:14 PM

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