Old school AC system compressor burned out

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Annoyed82
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Old school AC system compressor burned out

Post by Annoyed82 »

Hi all
Car is a 1976 Cadillac with the old Valve in receiver assembly that has run well for many years on R134 with no issues.

Last year it needed recharging I thought ok fine, its been 12 years between recharges. Then barely a year later, it stopped blowing as cold but compressor still turned, then the compressor burned out (you could actually see smoldering and an orange glow) and locked up. There were no funny smells or anything like that. System definitely no longer has any refrigerant in it.

These cars have a thermal fuse which is supposed to blow when refrigerant gets low in order to stop the compressor from burning out-that hasn't happened for some reason. I took it to a shop and he thinks refrigerant probably leaked out of the compressor seal, which is not surprising given its age. He also recommends replacing the dessicant bag inside the VIR as failed compressors can deposit crap in the system.

My question is why didn't the thermal fuse act to protect the compressor?
Thanks
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Cusser
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Re: Old school AC system compressor burned out

Post by Cusser »

I don't "know why".

But the original AC compressor in my 1988 Mazda B2200 truck did have a heat fuse - located in the receiver-drier - and that did blow out (actually cracked) and I lost all my R-12 at an intersection, waiting three light changes for my green light, 115F afternoon, Phoenix Arizona maybe early 1990s. I eventually installed a compressor designed for later year trucks which had a high pressure relief valve, and simply had a plug in the receiver-drier.
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JohnHere
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Re: Old school AC system compressor burned out

Post by JohnHere »

I'll take a guess about the thermal limiter: If it was the original part from 1976, it might have "silently" failed at some point, resulting in its inability to open and protect the compressor when something went wrong with it.

Also, you mentioned that this VIR system was converted to R-134a many years ago. VIR system conversions aren't known for very good cooling performance because one of the three VIR components (the POA valve) isn't pressure-adjustable, meaning that it can't be optimized for R-134a like a full-size POA valve can.

As far as you know, was the system cooling acceptably up to the apparent loss of refrigerant and catastrophic compressor failure?
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Annoyed82
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Re: Old school AC system compressor burned out

Post by Annoyed82 »

JohnHere wrote: Sat Nov 19, 2022 8:47 pm As far as you know, was the system cooling acceptably up to the apparent loss of refrigerant and catastrophic compressor failure?
Yes it was, I never experienced cooling with R-12 so can't make a direct comparison.
Thermal fuse was barely a year old

I've read the dessicant bag inside the VIR should also be replaced when replacing a compressor which looks like an awkward job.
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JohnHere
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Re: Old school AC system compressor burned out

Post by JohnHere »

It has been quite a while since I worked on or even saw a GM VIR system. If you want to take a chance, you could disassemble the VIR and replace the desiccant bag yourself. Desiccant kits are available in the market. Better yet, I think, is to purchase an entire VIR unit that has been rebuilt by a reputable company. Most, if not all, will also warranty it. This presumes keeping the system the original R-12 refrigerant.

If you want to use R-134a, like it was when converted, a VIR eliminator kit is also available. This will cycle the clutch on the A6, though, which was not meant to cycle. If you retain the A6 and go with R-134a, plus the eliminator kit, you should expect considerably shorter clutch life.

If it were my car, I would keep it the way it was originally designed: R-12 refrigerant and mineral oil, replacing the A6 and VIR, also replacing the condenser, and thoroughly flushing the rest of the components before evacuating and recharging it.
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tbirdtbird
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Re: Old school AC system compressor burned out

Post by tbirdtbird »

John, did these systems not have an LPCO?
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JohnHere
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Re: Old school AC system compressor burned out

Post by JohnHere »

If memory serves (and it has been quite a while), the Compressor Thermal Limiter Switch on a VIR system from the early to mid 1970's opened with a pressure anomaly on either the high or low sides. Once it opened, it couldn't be re-set and had to be replaced, like a fuse. I remember changing those switches during that time period, but I can't recall a separate LPCO.
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