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.

[-=Jeff=-]

Mine was the high side schrader valve.

This is a common failure point on our cars

[rush91]

A few years ago, I bought a can of 134 refrigerant. I was curious to see if my A/C even worked. I added the whole can, but no cold air. I kept getting the low freon code, so I pulled the fuse and it worked after that.....Blew absolutely ICE COLD after. I never got the code again, and it lasted the summer. When I pulled the car out in the spring, it had all leaked out over the winter. So i have a slow leak somewhere. But I don't even bother running the A/C anymore. If it's hot, I just roll down the windows or take the top off. And I always carry a bottle of water in the summer.

[mhobtr]

Low pressure switches are adjustable. A problem for R12 cars is that now, when you buy a replacement LPS, it is set for R134 and cuts off too soon. That was the problem I encountered but it went away after I got the LPS dialed in for the R12 setting in the FSM.

I wasn't impressed with the accuracy of the LPS for R134 either after I started dialing it in. If I remember correctly, it was about 2 PSI too high.

[mhobtr]

But I don't even bother running the A/C anymore. If it's hot, I just roll down the windows or take the top off. And I always carry a bottle of water in the summer.


You don't live in the South. Come down sometime in August and let us know what you think.

[rush91]

You don't live in the South. Come down sometime in August and let us know what you think.


I live in southern Illinois and it starts getting hot the second week of May....and by hot I mean I'm glad I don't have black leather, that would suck in the summer. I don't care where one lives, hot is hot. Come up here in August and I guarantee you won't able to tell here from there.

[TexasZR1]

I would love to have Illinois average temperature of 82F in August with record highs of 95 vs Houstons average of 94f with record highs of 105 and asphault temps of 120+ . Im quite sure we would agree its different!

[akool64]

If you install the later R134A compressor you will need to retain the old compressor hose adapter.
Coldhose.com can replace the old hoses and install new hose ends to incorporate R134A low and high service fittings. This company provides excellent service and is very reasonable.
While you are at it,, install a new orifice tube, 4 Seasons P/n 38638 and cycle pressure switch, p/n 36674.
This would be a good time to remove the radiator package and clean the debris from the cooling fins.
The system will require 2 lbs. of freon.
If you live in the Tulsa area I can give you a hand.

[gtcollins@maxnet.co.nz]

Don't know

Sent from my SM-G960F using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[gtcollins@maxnet.co.nz]

Don't know

Sent from my SM-G960F using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)Sorry was set by mistake

Sent from my SM-G960F using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[jss06c6]

Mine took 1.76 lbs of R134a

Sent from my SM-G950U using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[DRM500RUBYZR-1]

If you install the later R134A compressor you will need to retain the old compressor hose adapter.
Coldhose.com can replace the old hoses and install new hose ends to incorporate R134A low and high service fittings. This company provides excellent service and is very reasonable.
While you are at it,, install a new orifice tube, 4 Seasons P/n 38638 and cycle pressure switch, p/n 36674.
This would be a good time to remove the radiator package and clean the debris from the cooling fins.
The system will require 2 lbs. of freon.
If you live in the Tulsa area I can give you a hand.

WOW!
I am saving this one!
Talk about concise and correct, with all info needed!!!
Thanks for sharing this!
(Of course, I will have to take credit for it now as my own);)
:cheers:
Marty