A/C 134a Conversion

With the help of Tom Van's 134a conversion article on one of the INAS periodicals and Siegle's Coupe A/C conversion series in the CCA magazines last year, I bit the bullet and converted my '74 Bav from the old Behr Freon R-12 compressor system to a new Sanden 134a system hoping that our southern Louisiana summers will not over-tax my system. The compressor, its mounting bracket for our M30 block, dryer, and a new expansion valve came from Jim at Mesa Performance, 4 new barrier hoses with aluminum crimped fittings came from a local auto parts house, and the vacuum and 134a installation came from a local independent shop who was having a slow day and took pitty on me (thank goodness.....read on).

Details if anyone is interested:

I used the original evaporator, condensor, and fans. A Hayden replacement fan will go in front of the condensor but you have to remove both the radiator AND condensor units to get these into the nose of your car. And, the Behr fan that was still in my car is higher rated than the Hayden replacement, so let's hope it continues to work. Speaking of fans, make sure that the inline resistor from the on/off switch line to the compressor clutch and condensor fan is hooked up and working. There are no practicable "larger" replacements for either the evap or condensor units due to space requrements in the Bavaria's.

The Sanden 508 compressor is compatable with either freon or 134a, but came with mineral oil for R-12 already in the compressor. So I had to drain it completely and added new PAG oil per Sanden's instructions available on their web site. (PAG and mineral oil are NOT compatable, BUT mineral oil is used on the joints and fittings, so don't throw away this oil you drained out.....yet). The special compressor mount bolts driectly onto the engine block where the old Behr mount used to live, but one of the adjustable brackets hit the oil pan flange, so I made my own out of some angle bracket material.

The dryer MUST be of the 134a type, but there is no such thing as a 134a only expansion valve, so my new valve was identical to the old one which I replaced. HOWEVER, next time I'd just use the old valve if I knew it was still good, because you don't have to break the 3 seals where this valve fits onto your evaporator, greatly decreasing your chances for a leak here. You CAN test the expansion valve by iceing down the small capillary tube that is snapped next to the larger low press tube within the evap unit...if it is ok, the cold of the ice will allow the expansion valve to close proving that it is working ok. There is no ablility to bench test your evap and expansion valve joints, so you just hope and prey that your fittings are all ok. Since I replaced my valve with a new one, and after we charged up the system and ran it for a day, it leaked at the evaporator! This is not fun replacement duty, but after removing and reinstalling the evaporator, housing, and fan 3 times, I got pretty fast at it! Make sure that the capilary tube coming from the a/c temp switch fits neatly into the evap housing hole and in between the fins of the evap unit.

You MUST have new barrier a/c hoses made, but there are a few tricks I learned the hard way. Your new hoses need to be custom made with a variety of fittings and sizes on each end (4 different sizes of either straight, 45, or 90 degree angle flare, or 2 different o-ring sizes with either a 45 or 90 angles). You cannot use the old removable hose fittings (too bad...a good German invention) on the new barrier hoses as they will not hold the pressure nor are they of the same hose diameter. You can get close to the hose lengths using your old ones as a template, BUT since the Sanden and Behr units have their hose attach points in different places from each other, the hoses are not an exact match. If I had been sharper, I would have had each hose initially made up with only one fitting, then loosely installed each hose and marked where I wanted the opposite second fitting done. (I had to remake one hose 3 times!) The compressor takes o-ring fittings, the condensor and evaporator each use flare fittings, and the dryer takes flares, but I'd order a dryer with o-ring fittings next time and have the hoses made for them. (the o-rings hold much better that the flares, which are no longer used on any a/c systems in new cars now). The copper conical washers are extinct in most parts houses, and I had to order some as using your old ones is betting on a leak. Buy about twice of each size of what you need. The new flare fittings are aluminum and are designed to NOT be used with these washers, but we couldn't get them to hold pressure, so we installed these washers on all flares "wet" using the old mineral oil as a lubricant. Do NOT dry fit these joints and let your tech tighten them using TWO wrenches, as over tightening can ruin your flare joints! Also, one of my copper lines to the evap had a hair-line split, so I "borrowed" an identical part from my new parts car.

Now, get ready for having PLENTY of leaks! When you open up a system as old as ours is and as completely as I did (all joints and fittings open), most shops don't want to get involved with your project as it is quite time consuming ($$$) for you and him to track down and seal all your leaks....I had 6 or 7 over a 3 day period. I was going to learn to do this a/c stuff myself via Library books, etc. but am glad I spent the extra for a tech to vacuum and charge for me. He had a "hands-off" unit that completey evacuated down to 33" or so, held it there for 30 minutes via a digital timer, then charged it with 134a in 0.1 ounce units, oil, dye injection...all the bells and whistles. Then, out comes the digital 134 "sniffer" for minute leaks, and a black-light unit for detecting the dye he put in. On top of these expensive goodies, he had a digital thermomenter which he checked static outside air temps vs. those at the condensor, inside the car, and at both left and right sides of the evaparator unit. He got mine down to 45 degrees discharge in his shop, but said that when the oat gets over 110 on the highway, it won't be as cold. A DIYer could not afford these tools.

One thing he recommended that I did not install, is a low pressure cutoff switch. Next time I'll do this, as it installs directly onto a R-12 schrader valve that I had removed from my system when I converted to 134.....too late!

Whew....hoping and praying that I don't have anymore leaks.

Bruce Farrar

'72 and '74 Bavaria