A/C Compressor Upgrade

Post your E12 technical questions and comments here. Please, no off-topic posts.

Moderators: Mike W., Pierre

User avatar
528i-1981
Posts: 40
Joined: Wed Feb 07, 2018 5:50 am
Location: Boston North Shore, MA

Re: A/C Compressor Upgrade

Post by 528i-1981 » Tue Jun 12, 2018 9:12 pm

Gents - My AC blows cool-ish, let's say "tepid" - definitely something going on, but not cold. The Haynes manual is really sparse on the AC - a basic diagram of the components and the admonition to get thee to a refrigeration engineer with any questions. So my first hope was that a simple recharge would get me back in business, but I'm not sure if the PO has switched to 134a or if I'm still on R12. I inspected the system quickly from above and saw the dreaded red hose connecting the drier to the condenser. So I've got work to do.

First question - how do I verify whether the system is R12 or R134a?
Second question - evidently there's at least some refrigerant in the system. How do I determine the level?
Third question - is there a way to change out the hose without evacuating the refrigerant?
Fourth question - can I check/top off the compressor oil without removing it?

I know from Mike W's excellent FAQ that the drier needs to be swapped out during an R134a conversion - but the current drier looks original to me, and the red hose (with excellent patina) seems to suggest this might still be R12. It could also have been a hack conversion, but the compressor is still working, quietly at that.
(oo=00=oo)
1981 528i 5-speed

PatinaBeforePolish
Posts: 163
Joined: Sun Jan 18, 2015 1:22 pm
Location: Baltimore, Md.

Re: A/C Compressor Upgrade

Post by PatinaBeforePolish » Wed Jun 13, 2018 6:20 am

Good to know about the R12, I was considering doing the same conversion to R134 and a parallel condenser. If you switched to the parallel condenser, how were you going to mount it to the car? And the fan to the condenser? The stock unit has the brackets spot welded to the condenser frame.
78 F150
79 528i
81 528i parts car
01 540i
86 944

User avatar
Lock
Posts: 181
Joined: Sun Oct 04, 2015 1:51 pm
Location: San Jose, CA

Re: A/C Compressor Upgrade

Post by Lock » Mon Jun 18, 2018 11:37 pm

528i-1981 wrote:
Tue Jun 12, 2018 9:12 pm
Gents - My AC blows cool-ish, let's say "tepid" - definitely something going on, but not cold. The Haynes manual is really sparse on the AC - a basic diagram of the components and the admonition to get thee to a refrigeration engineer with any questions. So my first hope was that a simple recharge would get me back in business, but I'm not sure if the PO has switched to 134a or if I'm still on R12. I inspected the system quickly from above and saw the dreaded red hose connecting the drier to the condenser. So I've got work to do.

First question - how do I verify whether the system is R12 or R134a?
Second question - evidently there's at least some refrigerant in the system. How do I determine the level?
Third question - is there a way to change out the hose without evacuating the refrigerant?
Fourth question - can I check/top off the compressor oil without removing it?

I know from Mike W's excellent FAQ that the drier needs to be swapped out during an R134a conversion - but the current drier looks original to me, and the red hose (with excellent patina) seems to suggest this might still be R12. It could also have been a hack conversion, but the compressor is still working, quietly at that.
If you have the red hoses you most likely have R12 because R134a will just seep out of them. But then the conversion could have been a lazy job.

It's hard to tell the age of dryers because OEM and aftermarket ones pretty much all look the same. Their position above the exhaust and with exposure to road dust mean they all look equally dirty. Also, unlike the expansion valve which contains a little bit of refrigerant gas, and the R134a barrier hoses vs R12 cheese grater hoses, the dryer isn't specific to the gas used.

1. R12 and R134a fittings legally have to be different. Here's a chart for the sizes;
https://www.epatest.com/609/manual/manu ... c461181328
2. Get a ac manifold gauge set and check the pressures when it's running, the difference between what you should have and what you do have will show you how much is in there. According to this guide, R12 should be between 25-40psi on low and 200-225psi on high.
http://www.aa1car.com/library/ac_recharging.htm
3. No way to change out the hose without evacuating first. You can take it to a shop and have them just evacuate your system so that you can take it home and work on it.
4. You can top off the oil by either using an inline oil injector on the fill hose, or a can of oil refrigerant oil itself. But again you can't see what's inside the system without evacuating it first.

My system was tepid bordering on useless on a mild day, the pressures were low, and the sight glass was foamy so I knew it had some R12 in it. I have the user manual and near the back it said the car took 2.2lbs or so of gas (I think), so I got two 12oz cans and added them in, using both the pressure and the sight glass to monitor when it was full, and stopped when it was good. It cools really well, the air coming out the center vent is about 40F no matter the weather. After six weeks the pressures are the same so it was likely just never recharged for years and it seeped out the red non-barrier hoses.

As for the parallel condendser installation, the e30 guys generally get lengths of metal and drill holes in them in the right spots. Just google "e30 parallel condenser".
1979 528i 5-speed conversion G260/6
1979 Honda CX500

Post Reply