No cold air on idle at 750 rpm

[Al smog check]

Hi folks
new on this forum
i do not know if this the right place to ask for help
i have a 1997 pontiac firebird 3.8
100 % original and I try to keep it that way
last week I replaced the ac compressor ac drier and recharged it with 26 onzas of 134 gas
it cool pretty good
mom 1300 rpm or cruise ac temp is 39 f
at idle 750 rpm temperature drop to 72 f
outside climate temp is 80 f
gauges low numbers is 42 psi high numbers 240 f
electric fan both working when ac is on
thanks for your help
what can I check or replace to get it work on idle

[Cornbinder89]

Pressures are high, esp if those are at idle. High pressure can be cause by many things, too much refrigerant, not getting all the air out of the system (non condensable gas in the system) not getting heat transfer at the condenser are just a few that come to mind.
How much does the system call for? did you add that amount by weight? or did you go off the cans stated weight? they have been known to be off.
You didn't you evacuated the system with a vacuum pump, so I have to ask, did you?
Is the compressor cycling on and off or just stays on at all times?

[Al smog check]

Hi Cornbinder89
Thanks for your answer
The system requires 1.63 pounds of Freon
I did not vacuum the system
I added the gas by weight but I could be wrong since my dog knock out the gas cylender from my scale and I lost the exactly weight added to the car
The compressor stay on all the time

Thanks for your help

[Tom Greenleaf]

Late to chime in - sorry. Post 2.1 just said it wasn't vacuumed alone means do it again with a well held vacuum. Air is throughout if you had system open I think will raise pressures low and high which keeps compressor engaged if just by low pressure cut out not low enough.

This is a fairly low capacity system so accuracy is critical IMO to within 1 ounce but still spot on is better.

The not cooling well or at all at idle is most likely air and wrong charge seems to overcome that with higher RPM. I can't be certain but those two things have to be corrected to know if it would quit the odd behavior,

[Al smog check]

Thanks For your help
Really appreciate it

[Cornbinder89]

AIr in the system, Will do it every time.

[Cusser]

I did not vacuum the system

This mistake caused you time, money, and aggravation.

Hopefully you and others have now learned something....

[Cornbinder89]

This mistake caused you time, money, and aggravation.

Hopefully you and others have now learned something....

Good judgement come from experience, experience comes from bad judgment, we all, make mistakes, I often said I could do it wrong, learn from it and do it right, cheaper than paying someone else. This is not always true, but as long as no major damage (other than bruised ego) was done, learn from it and move on.