Troubleshooting AC leak before charging with R134a

[1991 Corvette ZR-1]

I have recently done an overhaul of items in the AC system and I am running into a leak when vacuum testing the system. So for the things I have done:

Rebuilt the compressor
New Condenser
New Accumulator/Dryer
New compressor hoses
New orifice tube
New pressure switches
All new o rings coated with Nylog Blue sealant

The compressor was filled with a little over four ounces of oil containing UV dye. The rest of the UV dye oil was put into the accumulator. Strangely, I pulled vacuum on the system for over an hour and 20 minutes and it maintained -30 in Hg on the low side and high side. It was not until I did a subsequent test due to paranoia that I can no longer duplicate the required hour of vacuum being maintained. The high side appears to hold vacuum while the low side is losing half of the vacuum in about 40 minutes in the attached picture. I have double checked the fittings to make sure they are not leaking but part of me thinks that is the case.

What all is isolated to the high side? What is considered low side focused parts? Part of me wants to charge the system and look for the potential leak with a UV light after a few drives. BUT the idea of a slow leak of R134a refrigerant in the garage does not sit well with me either.

Wanted to make sure I tried everything before giving in and having a shop leak troubleshoot. I would not think a leak decides not to leak one test then decides to the second time I test.

[XfireZ51]

Following this. I just installed a ?newer? condenser. In my vacuum testing, I am able to pull -29? vacuum but lose it all within an hour or so. I didn?t realize you could test high and low sides individually.

[1991 Corvette ZR-1]

Originally Posted by XfireZ51

Following this. I just installed a ?newer? condenser. In my vacuum testing, I am able to pull -29? vacuum but lose it all within an hour or so. I didn?t realize you could test high and low sides individually.

I pulled the new compressor hoses off the compressor and in the process of vacuum testing the system closed off now minus the compressor. There is a schrader valve on the compressor that will allow me to pull a vacuum on the compressor all by itself. So we will see if that unit can hold a vacuum as well. The condenser sat on the shelf for months until I removed the plastic fittings and was greeted with a loud pop and hiss so it was vacuum sealed and held it this entire time, I am going to rule that part out.

Knowing my luck, it will probably be the evaporator. Only way I can think of to check the system if these other parts check out separately, is charge the system and run it then look for leak with a UV light. Maybe pull the fan motor and peak in with the light to see if any leaks are showing on the evaporator.

I would strongly consider a custom eliminator pulley at this point! Pull it all off and lose some weight in the process.

[1991 Corvette ZR-1]

The compressor I rebuilt checks out. It maintained -30 inHg for three hours. Next step is undo the low pressure line from the top of the evaporator and the high side from the bottom portion of it. I will plug those ends as well as the ends of the new compressor hose and pull vacuum off the accumulator. If that maintains vacuum for an hour or more, I will probably have the answer I did not want that it is my 30+ year old evaporator that is leaking.

For the compressor, I just removed a few bits so I could thread an R134a adapter onto it to clip a connection to. I guess I should have more faith in my rebuild skills. The hose port closest to the fitting pulls the bulk of the vacuum. With just that plugged, the gauge pegs at -30 inHg but the moment you close off the valves, the needle slowly heads to 0. With both ports blocked, it holds no problem.

Small victories, I guess.

[1991 Corvette ZR-1]

Compressor, hoses, accumulator and condenser all hold vacuum. The high pressure hard line with switches on it to condenser is suspect. I isolated the hard line by capping off both ends and attached high vacuum connection to it. Cannot hold vacuum with over half gone in 40 minutes or so. I do remember the black plastic sleeve on the part nearest to the condenser needing to be cleaned due to repeat oil residue over course of a few weeks. However, the fitting was leaking previously and I figured it was just running down from the fitting to the black sleeve. Guessing the line is rotted or compromised beneath that hard sleeve.


So where would one find a good reproduction of this hard line? The L98 high side line and the LT5 line APPEAR to be the same. Still need to test the factory evaporator still in place.

[1991 Corvette ZR-1]

Old condenser and low pressure line attached to it check out, Im surprised. I isolated the hard line which would not hold vacuum, so I pressurized it and found the high side schrader valve is leaking. Ordered valve stem removal and installation tool along with valve stems.


https://www.amazon.com/gp/aw/d/B07HC...?ie=UTF8&psc=1


https://www.amazon.com/gp/aw/d/B0023...?ie=UTF8&psc=1

Was not exactly sure of the type of valve stem so I guess we will see.

[XfireZ51]

Originally Posted by 1991 Corvette ZR-1

Old condenser and low pressure line attached to it check out, Im surprised. I isolated the hard line which would not hold vacuum, so I pressurized it and found the high side schrader valve is leaking. Ordered valve stem removal and installation tool along with valve stems.


https://www.amazon.com/gp/aw/d/B07HC...?ie=UTF8&psc=1


https://www.amazon.com/gp/aw/d/B0023...?ie=UTF8&psc=1

Was not exactly sure of the type of valve stem so I guess we will see.

This is exactly what Marc Haibeck has said is the primary issue in AC leaks. The high side Schrader valve. He suggests putting a metal cap over it rather than plastic.

[Jagdpanzer]

Dorman has a brass cap for this purpose.
https://www.dormanproducts.com/p-80262-902-025.aspx


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[XfireZ51]

Originally Posted by Jagdpanzer

Dorman has a brass cap for this purpose.
https://www.dormanproducts.com/p-80262-902-025.aspx


Sent from my iPhone using ZR-1 Net Registry

Phil,

Assuming this works for our system after converting to R134a, correct?

[Jagdpanzer]

Far as I know they only work with GM style R134 service port fittings with internal threads. My 94 ZR-1 has this type from the factory. Earlier cars which were originally with R12 have the old styleR12 service port fittings.


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