Old school AC system compressor burned out

Friendly format provided to inquire about automotive a/c systems.
Archived Forum

Moderators: bohica2xo, Tim, JohnHere

Annoyed82
Posts: 3
Read the full article
Joined: Thu Nov 17, 2022 12:57 am

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
User avatar
Cusser
Preferred Member
Posts: 846
Joined: Sun Apr 24, 2016 6:29 am

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.
User avatar
JohnHere
Preferred Member
Posts: 1197
Joined: Sun May 13, 2018 10:20 am
Location: South Carolina Upstate - USA

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?
Member – MACS (Mobile Air Climate Systems Association)

Thankful for the responses you have received? Please consider making a monetary donation to this Forum.
Annoyed82
Posts: 3
Joined: Thu Nov 17, 2022 12:57 am

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.
User avatar
JohnHere
Preferred Member
Posts: 1197
Joined: Sun May 13, 2018 10:20 am
Location: South Carolina Upstate - USA

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.
Member – MACS (Mobile Air Climate Systems Association)

Thankful for the responses you have received? Please consider making a monetary donation to this Forum.
tbirdtbird
Preferred Member
Posts: 1241
Joined: Sat May 02, 2020 1:48 pm
Location: Texas

Re: Old school AC system compressor burned out

Post by tbirdtbird »

John, did these systems not have an LPCO?
When considering your next auto A/C purchase, please consider the site that supports you: www.ACKits.com
User avatar
JohnHere
Preferred Member
Posts: 1197
Joined: Sun May 13, 2018 10:20 am
Location: South Carolina Upstate - USA

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.
Member – MACS (Mobile Air Climate Systems Association)

Thankful for the responses you have received? Please consider making a monetary donation to this Forum.
User avatar
bohica2xo
Preferred Member
Posts: 1170
Joined: Wed May 11, 2016 4:12 pm
Location: Las Vegas, NV

Re: Old school AC system compressor burned out

Post by bohica2xo »

Servicing a VIR assembly is not difficult.

Remove it from the car. Clean it before you open it. Service kit will have the O rings and the desicant bag.

A clean workspace is a good idea. You may find that the old desicant had an issue with the 134a. Clean everything.

Various GM A6 compressors have had several switches installed in the head. What was actually there as LPCO, Overheat, HPCO etc. would depend on GM at the time. A full factory electrical diagram will tell the story. I would recommend spending the 20 bucks for the Mitchell subscription for this car.

Finally, you had a compressor fail. It may have spread debris in to the condenser. You should be flushing lines, and consider a new condenser to the more effective parallel flow types.

Very likely the line set has mufflers installed as well. These can NOT be effectively cleaned if they are contaminated with debris.
Annoyed82
Posts: 3
Joined: Thu Nov 17, 2022 12:57 am

Re: Old school AC system compressor burned out

Post by Annoyed82 »

bohica2xo wrote: Mon Dec 05, 2022 10:46 am Servicing a VIR assembly is not difficult.

Remove it from the car. Clean it before you open it. Service kit will have the O rings and the desicant bag.
Its the removal from the car that is proving difficult-the VIR unit has a huge nut that just doesn't move and there is a 2nd nut behind it on the line out of the evaporator. Does anyone have experience with removing these?
User avatar
JohnHere
Preferred Member
Posts: 1197
Joined: Sun May 13, 2018 10:20 am
Location: South Carolina Upstate - USA

Re: Old school AC system compressor burned out

Post by JohnHere »

If memory serves, I never had a VIR whose connections wouldn't budge like that. Must be due to external corrosion on the threads.

Only thing i can suggest is to spray them with Deep Creep or something similar every day for about a week. Then apply opposing manual force to the connections using properly fitting tube wrenches—one on each nut—to break them loose. Wear sturdy gloves while doing this to protect your hands.

It's tempting to use an oxy-acetylene torch in situations like this, but I don't think I would. Chances of overheating sensitive components is a definite risk.
Member – MACS (Mobile Air Climate Systems Association)

Thankful for the responses you have received? Please consider making a monetary donation to this Forum.
Post Reply