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No high side A/C port on my 73 corvette

Rooster on Sun August 31, 2014 10:28 AM User is offlineView users profile

Year: 1973
Make: Chevrolet
Model: corvette
Engine Size: 350
Refrigerant Type: R12
Ambient Temp: 80
Pressure Low: 30
Country of Origin: United States

I went to charge the R12 system and, lo and behold, there is no high side port on the 1973 corvette Small Block. In the Corvette forum there are lots of posts about the lack of a high port or sight glass. Compressor has an OE sticker on it that says 2.8 lbs R-12. This vehicle has 18k original miles so I believe this compressor is OE. It was 80* outside today. I charged on the low side and have about 30 lbs pressure when fully charged low side at the compressor. Pressure at the VIR low port is the same. I only have 60* at the vents and also 60* when I stick a thermometer in the evaporator case so I'm certain I have no duct problems. Without a high side pressure I am lost for diagnosing the problem. Was thinking about just ordering a VIR eliminator kit installing it, flush the system and see what happens. Wondering if any of you have any thoughts?
I own an Auto repair business and do have a R12 reclaimer.


Dougflas on Sun August 31, 2014 12:54 PM User is offline

I would not use a VIR eliminator. To get an idea what the high side is reading, measure the liquid line temp after it leaves the condenser. Then use a pressure to temp chart to convert to pressure. 30 PSI low side is right where you want it. My info says 3 1/4 lbs for 1973 vette . By the way, VIR's should have a sight glass.

Edited: Sun August 31, 2014 at 1:00 PM by Dougflas

mk378 on Sun August 31, 2014 1:01 PM User is offline

Those before and after pressures show that your VIR valve is wide open at 30 psi, as it should be. Put the interior fan on low and rev the engine and see if you can make it start throttling-- where it would be about 25 at the evaporator and lower at the compressor. Agree with Dougflas is that the most likely explanation is that the car is undercharged. You could recover and weigh how much comes out to see if there has been any major leakage.

Edited: Sun August 31, 2014 at 1:03 PM by mk378

Rooster on Mon September 01, 2014 7:33 PM User is offlineView users profile

Thanks guys,
More questions if I may.
No sight glass in the VIR.
I will suck the R12 out and measure in 3.14 lbs. Before I do I think I should either replace the VIR or put in an eliminator.
Douglas why do you not like the eliminator kit? I have read good things about it. It supplies an accumulator, a fixed orifice and a cycling switch so the compressor doesn't run all the time which is the system GM went to on the 77 up corvette. The VIR is original and 41 years old. Maybe if I stay with the VIR I should at least replace the desiccant pak but, it sounds like the VIR is functioning? Thanx mk378.
I found out that if you replace the manifold hose assy the new one comes with a high side port.
Not sure if I want to spend $165 for that. I will use the pressure to temp chart.
Still not sure what to do.


Dougflas on Tue September 02, 2014 1:05 AM User is offline

the sight glass should be located to the left of the suction line and the liquid line from the condenser. Yes, if the system was flat you should have changed the bag. I do not like eliminators because the the A6 was not meant to cycle due to the clutch area being small. Gm did go to cycling in later years but went to the R4 compressor with larger clutch area. The TXV and POA will give you better cooling if properly working. Before you recover the R12, why not just add some and see if it corrects your problem. As far as no high side, there was an aftermarket adaptor made for this purpose. It involved removing the liquid line at the Vir and placing this adaptor on the line and then into the VIr. There was a port on this adaptor. I do not remember who had made them; possible ARA but they are long since gone. I still have clutch hubs because of the cycling of the A6's. I also have replacement sight glasses for the VIR's so I am positive they had a sight glass.

Rooster on Tue September 02, 2014 1:37 PM User is offlineView users profile

I looked at replacement/ rebuilt VIR's online and where there is a sight glass on them, mine isn't there. I always get the odd ball LOL!
CONVINCED......I will not use a eliminator kit. Found an inline sight glass for 5/16 line. Will reclaim, put the glass in and recharge.
Thank you so much guys! I will let you know how it comes out.


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