I just took my first air conditioned ride in my bus after 11 years of having a non-functional air conditioning system. What a difference. I should have done this years ago.
To recap, I have an aftermarket dpd overhead A/C unit that I've seen quite a few of in 72-79 busses. Also a similar one in Vanagons. It's T-shaped with three vents in the front and two in the back. The condensor is mounted flat underneath the bus with forward-facing louvers on the bottom and two shrouded fans pulling air up through it. The original compressor was a York piston compressor that was mounted on the left side of the fan housing, driven by a dippy little thin fan belt that runs between the fan housing and the engine. Requires removing the fan to access the drive pulley. Besides the thin belt (which I hear is prone to breaking, and only available at the dealer - $15 each) the location of the stock compressor requires you to cut away a large amount of tin on the left side of the motor, making it hard to get a good seal.
I decided to try a different, unproven path. Years ago I took out the stock compressor, got replacement tin and sealed the engine compartment back up. I didn't want to undo this. Instead, I dug up the old pulley assembly that bolted to the fan which was supposed to drive the air pump. Took that off long ago too. A kind listmember sold me a Sankyo rotary compressor with some universal mounting brackets, which nearly worked as is to bolt the compressor where the air pump used to be. I had to grind down one of the brackets, use some spacers, and make one small bracket so the compressor could be adjusted. The compressor then bolted right in on top of the fan housing. I thought I was going to have to ditch the blower fan and stock air box for clearance but everything fit, although it's somewhat cramped in the engine compartment now.
Next I dropped the evaporator unit in order to disconnect the hoses from it. This was NOTFUN(tm). Took all of the old hoses off the bus, threw them in a box and took them up to an auto parts place that makes A/C hoses. $250 later, I had all new hoses. That hurt. Normally I would cheap out on something like this, but I had an A/C hose pop on me recently and it was a seriously scary experience. The old hoses did not look like they could take the 300+ psi that can be generated by the compressor, at least not for long. I had them make the new ones a little longer to account for the new location of the compressor. The low pressure hose was 19 ft long!! Holy crap! The high pressure hose was "just" 11 ft - it only had to go to the condensor.
Today I installed the new hoses and seals, put the evaporator unit back in. This was even more NOTFUN(tm), flushed out the condensor with oil and compressed air, flushed out the compressor with oil. Added some oil to the new evaporator/dryer, to the condensor, and to the compressor. About 8 oz total. There are two types of oil used with 134A. PAG and Ester. Ester is supposedly more compatable with the old R12 style oil, so I used that since I hadn't had the system formally flushed.
Tightened everything down, hooked up the wires, and fired up the vacuum pump. Pulled a vacuum on the system and it seemed to hold it just fine. Added a can of 134A then started it up. Pressures were good, no apparent leaks, so I put in another can. Temperature at the vents started dropping after the first can. Disconnected the gauges and took it for a spin. Everything works! The air temperature wasn't extremely cold (~60 degrees) but compared to the 103 degree outside air, it felt pretty good.
I couldn't really notice the drag on the engine. I'm sure it takes some hp, but not much. I did have to increase my idle to compensate but otherwise I can't tell the difference. I can still hold 65 on the freeway, although I'm not going to cruise that fast for a while because I don't want to stress the compressor.
A word about refrigerants. There are three available now: R12, which is the old standard, R134A which is the new standard, and Freeze-12 which is a relative newcomer. I have absorbed a LOT of information about refrigerants in the last few days and I am still not sure what to believe. Everybody has a different story and everybody is absolutely convinced they are right. I found the same to be true about CB antennas, but I won't even get into that! I strongly considered going with each of the three refrigerants, but I finally settled on 134A because it's cheap, I can buy it without a license, and there are a lot of cars on the road using it. Freeze-12 requires a license and is $8/can, and hard to find. R-12 requires a license and is $18/can and liable to go higher very soon. R134A is $3.50 can and you can get it at most auto parts stores.
Some people say that 134A will have a higher pressure in the system. My answer to that was to use less refrigerant. I currently have about 40 oz in the system and the maximum pressure on the high side is about 250 psi, which is well within the safe range. I saw 300psi on the R12 system in my car.
Some people say that 134A doesn't "carry the oil" in suspension as well as R12, and that it will cause your compressor to fail anywhere from a week to a year after you install it. My answer to that is that I have a modern, reputable brand compressor that is the same as what is installed in lots of other cars that are running 134A successfully. If it can work for them, it can work for me.
The evaporator is three feet above the compressor and condensor. I worry that the oil is all going to accumulate in the accumulator and not be carried UP to go through the evaporator (and then back to the compressor) because of gravity and because of the previous paragraph. This could cause the compressor to not be lubricated properly. My answer to that is to charge the system with a small can of oil/134A every year. The cans are $3 and contain 2 oz of oil and 2 oz of 134A. You can hook them up to the low pressure port and the contents will be sucked right into the compressor. I figure if I do this once or twice a year, the compressor will likely never starve for lubrication even it the oil doesn't circulate well. My new dryer is enourmous - it was made for a diesel truck the guy said. I'm sure it can hold a quart of oil. Adding 2-4oz/year, I should be okay for several years before I run into a problem with too much oil in the system.
So, I will depart for Jerome on Wednesday and drive 1,000 miles through the desert in 2 days. I'm thinking there is a 50/50 chance that my unproven, pieced-together A/C system will not survive the trip. Lots of things could go wrong - compressor could fail, drive pulley could fail, connections could leak, condensor fans could die, etc.. I will bring all of my tools along and try to fix any problems on the way, but I may arrive in Arizona all sweaty just like I did last year. We'll see. I'll be happy to answer any questions about the installation, as well as general A/C questions although at this point I'm mostly just passing on what others have told me.
[later David writes:]
Tonight I replaced the broken coupler in my smog pump
pulley assembly (which is being used to drive an A/C compressor) with a
modified (bwahaha) hockey puck.