AC issue after 134 conversion/repair

[EvanZR1]

So I had my AC system repaired while the car was up in Chicago with Pete, and it still didn't work after getting it back, so I took it to a local shop last week. Their diagnosis was the low side pressure sensor was bad and replaced it. They also said it was about a 1/2 pound low on refrigerant, so topped off the system. Said tested it and it was blowing cold, but did say something I think is a little weird. Basically said that if ambient temp is under 80, the system is cycling compressor too often and it will set a fault and you have to disconnect the battery to clear for it to work again.

When I picked up the car, I tried the AC on the way home, and it started flashing the light on the controller, so I figured I'd give it a shot to disconnect the battery and try again. Let it sit overnight with battery disconnected, then tried it the next afternoon when temp was about 79-80 degrees out, and it almost immediately started flashing the light on the AC controller, and when I checked the code, it was 09 (low refrigerant).

Any thoughts? Has anyone ever heard/seen what the shop is saying or should I find another shop to try?

[TexasZR1]

Thats exactly what my 1990 zr1 is doing. If i can get it to stay on, it will run solid for abut 10 minutes and you could hang meat in it its so cold. Not sure what mine is charged with though. Wondering if going back r12 (if it by chance has been 'converted' to r134) might be a solution after ruling out leaks.

From my experience with my converted 1991 camaro, the systems are doggy with r134a because the condensor and evap are too small. My 1991 camaro either short cycles or ices over the evaporator core.

Any chance another sensor is resulting in the ac being commanded off? Maybe the freon isnt low, but a high pressure switch, temp switch, low pressure switch, bad ground, poor connection is resulting in the short cycle? Any chance the issue is with the ac control unit? Would love to reprogram it to ignore short cycle cutoff.

[EvanZR1]

Just talked to the mechanic, and he said what's happening is exactly what he was afraid of and is because of the different pressure for 134a. His suggestion was either wait for it to get warmer out, or jumper the low pressure switch so it doesn't see the issue. Said there's still a thermal switch on the compressor and a pressure switch for the high side, so wouldn't worry too much about just jumpering the low pressure side. Guess we'll try that and see how it works. He did say he had the switch jumpered when he was testing and it was working fine.

[TexasZR1]

Low side shut-off would make sense. On mine, on a cold start, the compressor short cycles for about a minute before running solid for 5 minutes or more. Let me know how that goes for you. I may try it too.

[WARP TEN]

When the issue of 134a first came up in the 90s, I had Marc Haibeck convert my system to 134a. Following the advice of a GM service bulletin, he did not replace any of the major components, just made sure the system was completely empty of the old stuff and replaced the fill valve and a couple of minor items. It worked fine for the remaining years of my ownership and I assume it still does. You might call him and talk about the system. He might have some suggestions for you. --Bob

[EvanZR1]

So back to the shop today to double check things, and yes the refrigerant is actually low. So car will be going back in week after next (can't miss South TX ZR-1 BBQ) to try and find the leak and fix. My guess is the schraedar valve on the accumulator as when I was checking fittings after I got home, the 134 conversion fitting on it seemed a little loose. I was actually able to turn it (loosen) by hand and could hear air/gas moving. If it is the accumulator, does anyone know if I can switch over the newer (93-95) R134a version?* The add-on R134a fitting on the 91 unit sticks out a good bit and looks like it would make it pretty difficult to get a connector onto it.

[billschroeder5842]

Evan, I'm just curious where you take your ZR1 for work in the DFW area?

[EvanZR1]

A buddy with a C4 turned me on to Ace Car Care in Plano.
https://www.acecarcareplano.com/
I wouldn't ask them to fully rebuild an LT5, but the owner is familiar with C4s and C4 ZR-1s and has worked on a number of them. Real straight shooters and won't overcharge and will also be up front if they aren't comfortable doing something.

[32valvZ]

Wish I could find a shop Id trust for things like this. I have a similar issue. I recharged my already converted to 134a system last summer... it held until about a month ago I see the green light flashing again, low refrigerant code... Its leaked from somewhere, but I dont know where... I need an AC shop to look at it, cept, I really hate leaving my cars with anyone truth be told....

[TexasZR1]

You can buy a sniffer off amazon for $50 or less. No gurantees, but could help you find your leak. Mine was the high side schrader valve.