AC Compressor Questions

[WondrousBread]

Hi all. A few years ago I was driving through a suburb in my Rx7 with the AC on. I rarely used it, but the car did have (to my knowledge) the original air conditioning system from 1986. Regardless, I was driving along and there was a loud hiss noise and my entire windshield and sides of the car billowed a cloud of white steam that disappeared immediately, and my engine bay was covered in condensation.

My AC refrigerant evacuated itself through an o-ring (or somewhere, have yet to find the leak).

Now that I'm in the middle of rebuilding it, I decided to replace all the o-rings and convert to a modern refrigerant. I removed the compressor, tipped it over, and ZERO oil came out. The clutch bearing on the compressor is smooth, but when I turn the compressor by hand I can feel/hear metal sliding along.

I have two basic questions:

1. Is it normal for there to be no oil in the compressor? Since it was running when I lost pressure and it stopped immediately, I'm wondering if it didn't drain back properly. It also could've leaked with the refrigerant, since I don't know exactly where the leak was until I take apart all of the lines.

2. Is it normal for there to be a gentle sliding noise as I turn the compressor by hand? Or am I in for a rebuild/replacement

Thanks, Chris.

 

[Saabist]

That kind of rapid refrigerant release would have caused most if not all of the oil to be lost as well. It is likely the compressor was damaged, and given that it is over 30 years old replacement is not a bad idea in any event.

 

[Chris142]

What brand is the compressor? Some have a sump like an engine. Others are only lubed by the oil thats mixed with the refrigerant. The old style hoses are not a good choice for the newer r134a refrigerant. They should be replaced too.

 

[WondrousBread]

Originally Posted by Chris142
What brand is the compressor? Some have a sump like an engine. Others are only lubed by the oil thats mixed with the refrigerant. The old style hoses are not a good choice for the newer r134a refrigerant. They should be replaced too.


Its a Sanden SD-708. I recall someone saying once on the Rx7 Forum that turning the compressor over should drain it, but like Saabist said, it could be the refrigerant leak took the oil with it.

I'm pretty convinced based on turning it and listening to the noise it makes that I'm just hearing the pistons sliding in their bores. I can't find a rebuild kit, or I'd do it myself. A rebuilt compressor will cost something near $300.

I also found that the fittings are the newer R134 style, so it may not be the original compressor for the engine. The system had definitely been serviced (though the o-rings were black and not green, so clearly it wasn't correctly converted).

 

[Chris142]

Originally Posted by WondrousBread
Originally Posted by Chris142
What brand is the compressor? Some have a sump like an engine. Others are only lubed by the oil thats mixed with the refrigerant. The old style hoses are not a good choice for the newer r134a refrigerant. They should be replaced too.


Its a Sanden SD-708. I recall someone saying once on the Rx7 Forum that turning the compressor over should drain it, but like Saabist said, it could be the refrigerant leak took the oil with it.

I'm pretty convinced based on turning it and listening to the noise it makes that I'm just hearing the pistons sliding in their bores. I can't find a rebuild kit, or I'd do it myself. A rebuilt compressor will cost something near $300.

I also found that the fittings are the newer R134 style, so it may not be the original compressor for the engine. The system had definitely been serviced (though the o-rings were black and not green, so clearly it wasn't correctly converted).

That compressor has an oil sump. Most of the oil stays inside the compressor. There is a bolt on the side of it that allows you to drain and fill it.

DO NOT put a rebuilt compressor on it. They are all junk regardless of which company rebuilt it. Buy a brand new one. They don't cost much if you search around. Maybe rock auto?

 

[mk378]

The SD708 was used as a refit to replace some really terrible compressors fitted to 1980s Japanese cars like Diesel Keiki. A sudden blow out of all the refrigerant is not likely from an o-ring, more likely the relief valve popped due to over pressure. The condenser fan system is highly suspect.

 

[zzyzzx]

Originally Posted by Chris142
DO NOT put a rebuilt compressor on it. They are all junk regardless of which company rebuilt it. Buy a brand new one. They don't cost much if you search around. Maybe rock auto?


This. Even a cheap off brand new one would be better. I've used Compressor Works ones made in Korea, and so far,so good.

 

[JMJNet]

SD708 is still available out there just google it.
It has also many clones.

 

[Saabist]

Originally Posted by WondrousBread

Its a Sanden SD-708. I recall someone saying once on the Rx7 Forum that turning the compressor over should drain it, but like Saabist said, it could be the refrigerant leak took the oil with it.


That's a very common compressor in 1980s and 1990s vehicles, though the fittings vary depending on application. It does not have a sump so it very likely was damaged due to the oil being lost when the refrigerant blew out. You'll want to flush the system out and replace the expansion valve and drier in the event that any metal shards got into the AC system.

I installed a new UAC compressor in my Saab 9000 back in 2013. As I recall at the time it cost around $125. It is a Chinese clone of the Sanden compressor and has worked fine all this time. I checked the UAC catalog though and all they offer for your car is a remanufactured Sanden. There may be other Asian-made brands that will fit.

 

[WondrousBread]

Originally Posted by Chris142

That compressor has an oil sump. Most of the oil stays inside the compressor. There is a bolt on the side of it that allows you to drain and fill it.

DO NOT put a rebuilt compressor on it. They are all junk regardless of which company rebuilt it. Buy a brand new one. They don't cost much if you search around. Maybe rock auto?


The only "new" on I've found on Rockauto lists the brand as Sanden but that it is from "various manufacturers". Which likely means it is rebuilt and listed wrong. The pictured compressor also has different fittings than mine, whereas the pictured reman has the correct fittings.

Originally Posted by mk378
The SD708 was used as a refit to replace some really terrible compressors fitted to 1980s Japanese cars like Diesel Keiki. A sudden blow out of all the refrigerant is not likely from an o-ring, more likely the relief valve popped due to over pressure. The condenser fan system is highly suspect.


You'd be correct! After the blowout, I found that my condensor fan had been disabled by the previous owner by crudely slicing the power cable. It runs all the time, which means he probably didn't want to figure out why it was doing that and fix it properly, instead opting to cut the cable. I've fixed the cable, but that combined with what seems like a R134 conversion (which I believe produces higher pressures on previously R12 systems) probably is what caused it. I'll investigate the relief valve. Does that change my "new compressor" prognosis?

Originally Posted by zzyzzx

This. Even a cheap off brand new one would be better. I've used Compressor Works ones made in Korea, and so far,so good.


They don't have a listing for my particular compressor, but thank you. I will investigate different part stores near me to see what they have available too.

Originally Posted by JMJNet
SD708 is still available out there just google it.
It has also many clones.


I've found some listings for reman / clones, but they (like the "new" Rockauto listing) have incorrect fittings. I assume this compressor came with different styles - mine is one bolt holding down a single flange that captures both the hoses, with o-ring grooves machined into the compressor side of the flange.

Originally Posted by Saabist

That's a very common compressor in 1980s and 1990s vehicles, though the fittings vary depending on application. It does not have a sump so it very likely was damaged due to the oil being lost when the refrigerant blew out. You'll want to flush the system out and replace the expansion valve and drier in the event that any metal shards got into the AC system.

I installed a new UAC compressor in my Saab 9000 back in 2013. As I recall at the time it cost around $125. It is a Chinese clone of the Sanden compressor and has worked fine all this time. I checked the UAC catalog though and all they offer for your car is a remanufactured Sanden. There may be other Asian-made brands that will fit.


I'll be flushing the system anyways, and I'd intended on replacing the easily replaceable parts already as insurance. I'll be extra sure to inspect for any metal fragments. Thank you for checking the catalog for me, I'll be calling some parts places near me for quotes in case they have new ones.

Out of curiosity, why is it that all the rebuilt compressors are bad?

Thank you everyone for your input, I really appreciate the help. This is probably the only part of cars that I have never actually touched or worked on, so this whole system is new to me.

 

[WondrousBread]

Actually, one more question I've thought of. If my only concern with the new Sandens I have found is that the fittings are incorrect, could they be swapped from my existing compressor? The fitting itself looks cast into the rear part, but that is removable with a few bolts (unless there's more to it on the inside that I'm not seeing).

Thanks, Chris

 

[Saabist]

Originally Posted by WondrousBread

Out of curiosity, why is it that all the rebuilt compressors are bad?


It's problem with rebuilt auto parts in general. Recent years have seen a race to the bottom in quality, and the more complex the part the more likely shortcuts will be taken in the rebuilding process.

You are correct that the same basic Sanden compressor models came with many different types of fittings for different manufacturers. They are also popular in aftermarket AC systems and as a more efficient replacement for the old 2-cylinder compressors used on many cars from early AC systems up through the 1970s.

 

[Saabist]

Originally Posted by WondrousBread
Actually, one more question I've thought of. If my only concern with the new Sandens I have found is that the fittings are incorrect, could they be swapped from my existing compressor? The fitting itself looks cast into the rear part, but that is removable with a few bolts (unless there's more to it on the inside that I'm not seeing).

Thanks, Chris


That's actually the cylinder head. Might be interchangeable between the same model of Sanden compressor, but I really don't know for sure. The valves are actually in a plate between the cylinder head and the main body. Here is a service manual for Sanden's "SD" series of compressors which shows some details of the contruction:

http://www.sanden.com/productlibrary/manuals/SD_Service_Guide_Rev_2.pdf