Climate Control

R-134a DIY Conversion

R-134a DIY Conversion

I converted my SO's 1985 BMW 325e from R-12 to R134a on the weekend. The R-12 had completely vamoosed---following an accident by my SO last fall/winter, it is my belief that the shop did not refill the system (the condenser got squished in the encounter) but I cannot prove that they did not fill it.

Anyway (sorry this is not on a P-car but ...)

I used the Castrol conversion kit---about 20$ from Pep boys--this contains O-rings, fittings, schrader valves and R134a PAG oil.

3 12 oz cans R134a: about $5 ea
charging hose: about $12

I changed: the receiver/dryer and expansion valve with 134a compatible parts from my BMW parts guy: these cost about $80 incl shipping

Change All O-rings----this takes a while
Add PAG oil
Change all Schrader valves---make sure you have the valve removal tool $2 at Track auto, but I had to stop and go get one.
Change receiver dryer---need an R134a compatible receiver-dryer... an R-12 one will break up and ruin your compressor
Change expansion value---this is under dash and somewhat difficult to get to in the BMW... don't know about the 928's [Open the hood. it's under the plastic tray just in front of the windshield. -Editor]
----R134a takes a different expansion valve than does R12--- I do not know what happens if you don't change it

Note: I have heard that some peple have had trouble removing low press and high press switches in one piece (in rec/dryer). Some say to save yourself the trouble and recommond replacing these while-you was at it.

Vacuum out system for about 45 minutes.
I bought a Bernoulli vacuum pump from JC Whitney. It works off your air compressor. It costs about 60-odd bucks.
Harbor Freight lists one for much cheaper---but I could not get them to sell me one. Ordered it twice, never got anything, no bill, no nothin' What gives with that company????
Some people claim you can reverse the flow in an electric tire pump and use it successfully---I do not know if this is true.

BTW, despite mfg claims, I could only pull about 22-25 in of vacuum with my 5hp 4.8CFM @ 120psi air compressor (6.something CFM at 90 PSI). The Whitney pump is claimed to pull 30 in of vacuum at 4.5 CFM at 90 PSI, but I'll be dammed it I could make that happen. I did not have any freeze up problems once the AC was charged and running so I'm guessin' I pulled enough water vapor out of the system.

I purchased an R134a gauge set from Whitney too----about $120---I found out later that Pep Boys and Track sells the same thing for less-----oh well, not enough less to do the return and all...
It is really nice to see that the readings are all correct, and that the fill is good etc.....It also makes the neighbors think that you know what you are doing. Some claim these gauges are poor quality but they worked fine for me.

I also bought Whitney's Air Cond "MasterCool" shop manual. $17 bucks.....separate fact from internet fiction in the change over. It is always nice to know, or think you know, what you are doing.....

It works great. Blows nice and cold...It works better than it has in years.

The tools were the biggest cost to do the job, but I've got two other cars that will need the conversion.
I also do not trust AC shops to do the work correctly---I'm certain many do a fine job, but I hear so many "leaks out in two days" horror stories that I have become skeptical. Given the time it must take to chage all the O-rings and do the Vacuum, it would have to cost $$$ to make this job worth anyone's professional time---and an 85 BMW probably isn't worth that kind of money for most people; hence shops would take short cuts to make the job more affordable (Just my opinion)

Total time---I'll bet it took me somewhere between 6-8 hours counting all trips to the tool chest, auto store, stopping to read the AC manual , to the fridge for beer, stopping to read the manuel... and all.. Changing out all the O rings does takes time....

Last Tip: jump the leads on the low pressure switch to get the compressor to come on initially when you are starting the new charge. After a minute of charging, it will have enough pressure on its own. Also put oil in the compressor ---not just in the reciever-dryer---to safe guard the compressor at initial start up.

Next---on to the 1983 928S climate control....Me thinks I will need to send out the "no so smart brain" to be rebuilt (why do they call it a "brain" when it wants to blow hot (or sometimes not at all) in the summer??). Because of the brain surgery, the 928 will not be as cheap ----If you thought the BMW was cheap (sans tool bill). But then. no repair on a 928 is as cheap as the equivalent repair on the BMW....
No flames....just a fact.

Keep cool, I know my SO is even though I'm boiling in my " automatic climate controlled" 5-sp 83S. Whoever put the "Sub-Tropic Sahara" setting in the climate control should be made to use it.


Convered my SO's BMW 325 (1985) more than two weeks ago. Everything is still working well.

Some comments on performance for the interested.

At speed (25 mph or so and up) there is no difference in AC performance. At idle, in stop and go traffic, R134a does not cool as well as R-12. This is as advertised in AC manuels. R134a needs more air flow over condensor to cool as well as R-12. If this really matters to you, some manuels suggest extra/bigger fan.


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