Help! 1981 AC problem

[Granpooba]

Yeah,I have allot of Ideas! :L
But you probly won't like'em!!:L
I need more information!!
Are we using Real R-12??
Are we using Johnsen's Freeze-12??
And what kind of Pressures are we running,High Side /Low Side??
(When the compressor is running!)
What is the Humidity??
What is the Ambient Temp??
What is the Engine Coolant Temp??
Are all the Air Deflectors in place around the Radiator and Condenser??
Is your Radiator and Condenser free of deb're??
Is the Evaporator free of Lint,Leaves,Mouse Nests,or other obstructions??
What is the AC Discharge Air Temp when it runs before it go's Hot??
What is the Low Side pressure when the Compressor shuts down??
What is the High Side pressure when the compressor shuts down??

Hmmmmmmmmm ........ you must think that I am a rocket scientist !!
Nope, just a retired Corporate Pilot.

My Vette is completely stock all original, except it was converted from R-12.

Considering the fact that I do not have all the tools or knowledge to work on this problem and that I am due for an oil/filter change/State Inspection.
I have made an appointment with our local Chevrolet dealership, who has a decent Vette mechanic. I have asked them to diagnose the AC problem and advise me of what is causing this problem. Not authorizing them to make the fix, just check it out.

I feel that this is the easier route to follow, rather than answering all those questions !! :L

Will let you all know what is found ...... and thanks for all of your input.

 

[6880 Mike]

...Any more ideas?...

Take her to a qualified automotive AC shop and let them test the system.

 

[Granpooba]

Take her to a qualified automotive AC shop and let them test the system.

Took it to our local Chevrolet dealer for a Lube/Oil/Filter change and state inspection. While there I asked them to check out the AC system as it blows ambient air after a few minutes.

Well they checked it, said it was one pound low on freon. They serviced it and said it was blowing nice cold air.

I picked up the car late in the day and drove directly to a resturant to have dinner with my wife. On the short trip I turned on the AC and Whaaaaaaaaa Laaaaaaaaaaaaa, nothing but HOT air came out. I called the dealership while having dinner and questioned them about this fix. They said to bring it back in and they will check it out again.

The car is now sitting at the dealership with a part on order. Not exactly sure what part it is and presently all that I know, it is some type of switch.
Will be learning more about it, in the next couple of days.

If this switch does not remedy the problem, then the car will go straight to a strictly AC shop. Am I loosing faith in GM products and the service ?
Yes I am !!

Will keep you updated.

 

[geekinavette]

The car is now sitting at the dealership with a part on order. Not exactly sure what part it is and presently all that I know, it is some type of switch.

Now where do I recall seeing mention of a possible switch sticking.... (sorry just had to :L )

The way the system works (in a very basic sense)...when the compressor is off the "high" and "low" (pressure) sides are sitting at the same pressure level...usually 70-100psi depending on the type of refrigerant. When the compressor turns on, the high side pressure increases and the low side pressure decreases. The orifice tube is a fixed (or it can be the variable type) restriction in the system that separates the high side from the low side.

There are two cutoff switches, one in the high side one in the low side.

If the high side pressure gets to be too high, that switch will open shutting off the compressor. Once the compressor shuts off, high side pressure starts to drop, low side pressure starts to rise (going back to the "equalized" state between high and low sides). Once the high side pressure drops below the switch threshold the switch closes again and all is normal again. (it is quite unusual for the high side switch to trip).

The low side switch is the one that normally cycles to keep the system pressures normal. When the low side pressure drops below a set threshold (usually around 30psi) it shuts the compressor off. Again...once the compressor shuts off the high side starts to drop, low side increases, until the low side pressure increases enough to allow the low side switch to close again. The operation of the low side switch also serves to prevent the compressor from running if there is insufficient charge in the system.

Ideally the charge is such that the difference between high and low sides is as large as possible. This means that the low side runs right at the switch threshold...but not low enough for it to trip and shut the compressor off. Now the entire system pressure will vary with ambient temperature (and other factors), so a system that is just perfect on a 90 deg day may very well cycle on and off on a 80 deg day.

Am I loosing faith in GM products and the service ?
Yes I am !!

"Products" require maintenance...regardless of who makes them. Even the most basic switch is still a mechanical device...and mechanical devices fail! It happens. Where the shortcoming is becoming more and more prevalent is in the service industry. It seems that the stories detailing poor service from a dealership are just piling up.

This is where forums like this become invaluable! With a little understanding of how a system works we're more able to double-check a repair, or even provide the technician with more valuable information.

Well anyway, good luck getting the AC to "chill"!

 

[bill81vette]

If you want the Phone # to my contact let me know and I'll PM it to you.
he used to own saratoga radiator in saratoga springs before he closed it and retired

He does do some volunteer work and is involved with the local NCRS chapter

I did see him last week and mentioned about to you to him and he had know problem with working on your vette!!!

 

[Granpooba]

If you want the Phone # to my contact let me know and I'll PM it to you.
he used to own saratoga radiator in saratoga springs before he closed it and retired

He does do some volunteer work and is involved with the local NCRS chapter

I did see him last week and mentioned about to you to him and he had know problem with working on your vette!!!

Hi Bill,

As of this Sunday, part has not yet come in for the AC in my Vette.
When the part does arrive and is installed, if it does not fix the problem, then I may very well be asking you for your friends number in Saratoga.

Thanks for your advise and help ...............

 

[Granpooba]

Just picked up the Vette from dealership.
Did not have time to chat with service rep., as I was in a hurry.
Work order states that they replaced " Cut Out Switch ".
Make sense to you fellows ?

Does seem to be working fine.

Thanks for the input..............

 

[geekinavette]

Just picked up the Vette from dealership.
Did not have time to chat with service rep., as I was in a hurry.
Work order states that they replaced " Cut Out Switch ".
Make sense to you fellows ?

Yes...both of the high pressure side and low pressure side switches are called a "cut out switch". A sticking low pressure cut out switch will result in the symptoms you described.

Just out of curiosity...what did they charge you to replace it?

 

[Granpooba]

Yes...both of the high pressure side and low pressure side switches are called a "cut out switch". A sticking low pressure cut out switch will result in the symptoms you described.

Just out of curiosity...what did they charge you to replace it?

They did not charge me to diagnose the problem the second go around, after originally finding that the freon was one pound low.

Total bill for parts and labor = $111.00
Of which $44.00 was for the part. The rest was labor and taxes.

Just out of curiosity ..... sound high ? Was thinking that perhaps the part could have been obtained from maybe Ecklers, at a lower cost.

 

[geekinavette]

Just depends on which switch it was. A typical low side cutout switch costs about 20 bucks, and takes all of 30 seconds to replace.

While we find your parts, please enter your ZIP Code at CSK Auto

Now if it uses the in-compressor type switch....that's a different story (I doubt your 81 does).

 

[bill81vette]

what dealer did you use whiteman's,maltbie's or whalen's?????

 

[Granpooba]

what dealer did you use whiteman's,maltbie's or whalen's?????

Whitemans' !

They also service my 2002 TrailBlazer, that I bought new from them.

 

[bill81vette]