A.C. Problem 1970 vette
Thread Starter
Instructor
Joined: Feb 2007
Posts: 190
Likes: 0
From: shrewsbury Pa.
A.C. Problem 1970 vette
Hey gang. After replacing all of the WORKING parts of the A.C. system, compresser, expansion valve, receiver drier and all hoses, and having the P.O.A. valve re-built by classic air. The system WILL NOT accept a charge. Something seems to be blocking the low pressure side and not allowing freon to be drawn in. High side evacuates fine. Low side evacuates so quickly, that most likely only the hose it self is evacuating, not the low side of system. Any Ideas before I just sell the whole car out of exteme frustration. Can't find a shop in my area the specializes in these older systems and trouble shoot it for me. My guess is the P.O.A. re- build. They were the weakest and most problematic part in these systems as I remember anyway. HELP.
Race Director
Joined: Sep 2001
Posts: 10,560
Likes: 439
From: Wellington, FL
St. Jude Donor '11 thru '25
I had a similar problem a while back and it ended up being a bad gauge hose. Try switching the high pressure hose with the low pressure hose on the gauge set and see if you can charge the system. Also, I'd replace the schrader valves on the car. You might also hook up your vacuum pump to the high side only and after you've pulled a good vacuum, push in the schrader valve on the low side and see if your vacuum is lost. This should tell you if there is something blocked in the system. It sounds like something simple to me. Good luck. 
Melting Slicks
Joined: Jan 2003
Posts: 2,877
Likes: 13
From: Doha
St. Jude Donor '08
did you replace the drier? and if yes, did you install it quickly as not to let humidity accumelates inside?
Also, old POA valves are very easily cloged by debris, did you replace that with a new original or upgraded one?
Also, old POA valves are very easily cloged by debris, did you replace that with a new original or upgraded one?
Le Mans Master
Joined: Jun 2006
Posts: 6,399
Likes: 1,226
From: Tampa Florida
I had a similar problem a while back and it ended up being a bad gauge hose. Try switching the high pressure hose with the low pressure hose on the gauge set and see if you can charge the system. Also, I'd replace the schrader valves on the car. You might also hook up your vacuum pump to the high side only and after you've pulled a good vacuum, push in the schrader valve on the low side and see if your vacuum is lost. This should tell you if there is something blocked in the system. It sounds like something simple to me. Good luck.
Thread Starter
Instructor
Joined: Feb 2007
Posts: 190
Likes: 0
From: shrewsbury Pa.
I had a similar problem a while back and it ended up being a bad gauge hose. Try switching the high pressure hose with the low pressure hose on the gauge set and see if you can charge the system. Also, I'd replace the schrader valves on the car. You might also hook up your vacuum pump to the high side only and after you've pulled a good vacuum, push in the schrader valve on the low side and see if your vacuum is lost. This should tell you if there is something blocked in the system. It sounds like something simple to me. Good luck.
Thread Starter
Instructor
Joined: Feb 2007
Posts: 190
Likes: 0
From: shrewsbury Pa.
Yes, replaced drier and quickly covered and sealed the ends for a couple of weeks until I was able to assemble the rest of the parts for the system.
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Thread Starter
Instructor
Joined: Feb 2007
Posts: 190
Likes: 0
From: shrewsbury Pa.
Melting Slicks
Joined: Jan 2003
Posts: 2,877
Likes: 13
From: Doha
St. Jude Donor '08
again I am not 100% but someone will correct me if I am wrong.
Thread Starter
Instructor
Joined: Feb 2007
Posts: 190
Likes: 0
From: shrewsbury Pa.
I think moisture will contaminate the drier even if you seal the ends for the period of two weeks. you need to either fill with freon gas or vacuum all the air out. I always leave the drier sealed inside the house till the last moment of installation then I rush to the nearest a/c shop for vacuum and fil.
again I am not 100% but someone will correct me if I am wrong.
again I am not 100% but someone will correct me if I am wrong.
Le Mans Master
Joined: Jun 2006
Posts: 6,399
Likes: 1,226
From: Tampa Florida
Here's a link to a site that covers adjustments made to POA Valves in older systems.
http://www.autoacforum.com/messagevi...&threadid=7567
http://www.autoacforum.com/messagevi...&threadid=7567
Melting Slicks
Joined: Jan 2003
Posts: 2,877
Likes: 13
From: Doha
St. Jude Donor '08
You are right, in my humble openion, the old POA valve should never be used even if its a new NOS. Its always a better idea to use the updated electrical cycles ones. I know someone will be upset about not keeping it original, but I am talking about DD vettes here.
Thread Starter
Instructor
Joined: Feb 2007
Posts: 190
Likes: 0
From: shrewsbury Pa.
Here's a link to a site that covers adjustments made to POA Valves in older systems.
http://www.autoacforum.com/messagevi...&threadid=7567
http://www.autoacforum.com/messagevi...&threadid=7567