A/C issues

diablostang · Jun 18, 2009

Trying to get my A/C working.. it has a new compressor and a new lower liquid line. My A/C blows cold when charged but the pressure spikes WAY too high to be safe, so I can't run it. I've run A/C flushing fluid through the lines and blown air through them all, don't appear to be blockages?

Any ideas?

Oh and this is in my 91 5.0

67coupe · Jun 18, 2009

How do know the pressure is spiking too high? Did you use gauges? If so, what was the ambient temps, engine rpm, and high and low pressures?

LaserSVT · Jun 19, 2009

Did you evacuate the system and put a vacuum in it?

diablostang · Jun 19, 2009

67coupe said:
How do know the pressure is spiking too high? Did you use gauges? If so, what was the ambient temps, engine rpm, and high and low pressures?

One of my friends put gauges on it and vacuumed the system before charging. He wasn't sure off the top of his head why it would be doing that, especially after cleaning it all out.

I forget the exact #'s off the top of my head. This was last fall. When it got cold I quit messing with it, but it's going to be in the high 90's here today and I'm tired of sweating. lol

I guess i'll have to clean it out again, hook it all back up and vaccum/charge it and see what the pressures are at again.

jrichker · Jun 19, 2009

Two reasons for high head pressures in A/C systems:
1.) Air still in system: you need 28.5" of vaccum for a minimum of 30 minutes at 80 degrees or higher temp to get all the moisture out of the system. I recommend that you close the hood and drive the car around until the under hood temps come up to the point that it is uncomfortable to put you hand on the engine.

2.) Insufficent airflow across the condenser while charging the system. A big fan blowing air into the condenser will help hold the head pressure below 350 PSI.

67coupe · Jun 19, 2009

jrichker said:
Two reasons for high head pressures in A/C systems:
1.) Air still in system: you need 28.5" of vaccum for a minimum of 30 minutes at 80 degrees or higher temp to get all the moisture out of the system. I recommend that you close the hood and drive the car around until the under hood temps come up to the point that it is uncomfortable to put you hand on the engine.

2.) Insufficent airflow across the condenser while charging the system. A big fan blowing air into the condenser will help hold the head pressure below 350 PSI.

You can also spray the condenser with a garden to help the system equalize.

We really need to know the high side pressure. It may not of been that high. My 134 conversion creeps over 250 psi on really hot days.

To add on to what jrichker said about airflow. If you have an electric fan, make sure it's on when running the A/C.

diablostang · Jun 19, 2009

jrichker said:
Two reasons for high head pressures in A/C systems:
1.) Air still in system: you need 28.5" of vaccum for a minimum of 30 minutes at 80 degrees or higher temp to get all the moisture out of the system. I recommend that you close the hood and drive the car around until the under hood temps come up to the point that it is uncomfortable to put you hand on the engine.

2.) Insufficent airflow across the condenser while charging the system. A big fan blowing air into the condenser will help hold the head pressure below 350 PSI.

IIRC the high pressure was spiking to around 400 PSI. I've got the stock clutch fan on the car and have never had cooling issues. It seems to work alright.

Suppose my condenser was beat up.. would that cause these issues? It's looks like someone drove down a road behind a gravel truck without the front bumper on.

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