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1990 Caprice a/c compressor exploded. Trans is leaking like a sieve

So I am on my way home after an honest 8, and I make it a mile down the road and goose the old girl a little off a stop light. Well next thing I know we have smoke rolling out under the hood, well it turns out the “smoke” was r134 refrigerant. The guy that recharged it said that the compressor failed and that its common with retrofits because 134a runs at a higher pressure.

Now I don’t need a/c, and I might just leave it as is, but it would be nice to have the old girl working 100%. It also turns out that the front seal of the transmission is leaking, I am debating whether or not to just have the transmission rebuilt. it shifts fine but its gotta come out anyway. Its a 700r4 and the trans guy recommends stronger 3-4 clutches and a shift kit to make the holding pressure higher.

Any advice.

Make sure the folks who work on your AC going forward have enough experience in auto-AC principles to know not to overfill the refridgerant. The systems are differerent car to car, and overfilling can damage the compressor and other components.


A guideline to R134a retrofit (R-12 was the only game in town when your car was built in 1990)

Charge only 80 - 85% of the original refrigerant amount.


Sticker says 3 pounds of R-12

Charge 39 - 40 ounces of R-134a.

Some older compressors are less tolerant of R-134a.

You might need updated pressure switches

You might need a larger condenser

You might need additional electric fans which come on with the AC

The A/C compressor did not give up because of a retrofit and high pressure. It likely gave up due to age, high miles, and a problem with the refrigerant oil; either not enough oil during the retrofit, loss of oil during operation, or the wrong type of oil added.

Fixing the A/C will be expensive and require a compressor, accumulator, system flushed, etc, etc.

Doing the A/C and transmission both would probably put you well north of 3 grand and nearer 4.

If the transmission is shifting fine I’d just reseal it, change the fluid and filter, and leave it as is.
The '88 and newer 700R4s are pretty good transmissions; it’s the '87 and earlier that could be problematic.


I’ve seen compressors blow seals because of overcharging

I was throwing that out there as a possibility

I was wrong, the car has the THM200-4 Transmission, I climbed under and identified it. I always heard these were weak, I usually drive this car gently but every once and a while I romp on it.

DB, please understand that my comments were directed to the OP and not you. Just clearing that up and I do have much respect for your opinions.
The exact reason for the compressor failure is not known but if it’s a matter of a shaft seal gone bad or manifold rings given up I would suspect 24 years of age rather than high pressure.

If high pressure due to 134 were the cause then it should have given up during the retrofit, whenever that was.
Personally, I’ve never seen the slightly higher pressures of 134 as being off enough to blow things up.
My memory is hazy on this but I also think that GM cars of this era and many others use a high pressure cut-out switch that turns the compressor off when the head pressure starts to get too high.

As for the transmission, that transmission in the car is a heavy duty version of the regular 200 and is used in GM high horsepower applications such as Corvettes, Buick Grand Nationals, etc.
My opinion would still be to just reseal the transmission, along with the engine rear main seal, change the fluid/filter, and be done with it.
It also might be a good time to check U-joints while the driveshaft is out.

@ ok4450

I am not actually sure where the compressor blew all of its freon out at, do they have a relief valve?
I probably won’t fix it at this point.

I think they used a 700r4 and a thm200-4 in the 1990 caprice? What are the differences between the two? Good point on the rear main. I may pull it myself, but I don’t have alot of free time right now and Im getting tired of laying on the ground so I might just pay to have it done.

Its more of a toy than anything, but I do enjoy the car and she had put some commuting miles on it and it serves as a great backup. I am not planning on exposing it to salt though, they body is not perfect but its in great shape.

No relief valve and I’m not aware of any car maker that uses one. Many years ago VW used a pop-off plug for a while but the EPA probably brought that to a halt. When the head pressure got too high the center of a brass plug would blow out and instantly vent the refrigerant into the atmosphere. Somewhat of a crude way of doing things…

You might have to do a net search for the differences because I have only messed with a few of these and it’s been a long time. The 700R4 (basically a TH 350 with an overdrive) was essentially used on Chevrolets if I remember correctly and the 200 was a lighter duty version of the TH350. The 700R4 eventually became the 4l60 which became the 4l60E…
The 200 became the 200R4 which meant an overdrive was added and I think the bolt pattern would allow the transmission to mate up to not only Buick, Olds, and Pontiacs but Chevy also.
Normally, the bell housing bolt pattern of a Chevy is different from the BOP transmissions.
This is all ancient history to me except I’ve been waiting myself for the right deal on a TH200R4 to use on a project.

My parents used to have a Caprice and kept it after retiring it as the family car. It was used for many years afterwards for misc chores and my late mother sold it (someone actually bought it, go figure) after my father passed away. That car had right at 410k miles on it and both transmission and engine had never been torn into for any reason. It still ran, drove, and shifted well but was a bit ragged around the edges… :slight_smile:

Did the “guy who recharged it” actually LOOK at the car and determine the compressor was the problem? Sounds more like a blown hose…How many miles on this car? Have you tried a can of tranny stop-leak?


No it just happened and I will probably have him look at it, it may be a hose that blew, that would actually be good news. It has around 90k original miles, Its a verified original 90k.

I didn’t try stop leak, I guess it cant hurt. Any brands you recommenced?


I am looking for a good, cheap 200r4. That combo does not exist.

Update- The a/c I never messed with, its still broken. The trans I paid to have it resealed and a new rear main put in. Its doing well.

@ok4450, I think by 1990, all GMs were using one type of engine in each of the size and cylinder options. For example, the same 4.3L V6 was used in all cars and light trucks sold as BOP or Chevy. The same for the Vortec V-8 used in all small block applications, and the 2.8L smaller V6, and most of the 4-cyl applications, except for the re-badged Asian cars, like Geo.

The only thing I’d worry about with a THM-200R4/700R4 swap is the electrical connections for the torque converter lock-up and the overdrive activation. These are the only electrical connections, but I don’t know if they are interchangeable. There are separate modules to control the 700R4 if the computer connections are not compatible. If Tester or Transman are around, maybe they can answer that question.