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Ok, Zee, here's my thoughts:
I've only been lurking on airconditioning.com. I'm a mechanical engineer and I do a lot of work on industrial chiller units. Several of the technicians that work under me do automotive A/C work on the side. They told me about the website and I've been keeping up with it ever since.
I'm not using new hoses. My '92 should have barrier hoses. Actually, I think there's a high probability that you've got barrier hoses on that A/C system you pulled from the '85. Volvo has always looked to the American supply chain for A/C equipment. Was Detroit using barrier hoses in the US market in 1985? You bet. Do you think that Volvo would have spec'd an American expansion valve, heater control and condenser, but a different style refrigerant hose? Probably not. Chances are, your hoses are fine.
My A/C tech buddies at work tell me that they see refrigerant losses at leaky O rings, leaky connection fittings and leaks in the aluminum lines where they enter the condenser (the lines rub on the frame and perforate). Oh yeah, leaky evaporators (a problem near and dear to the hearts of our 850 brothers and sisters). They don't see it through leaky hoses.
Oh, the $45 kit I was talking about was for Autofrost. It included 2 cans and a tap.
I'm planning on putting my new oil in at several points in the system. Most of the oil collects in the condenser, anyway. Once I have the accumulator/drier and compressor removed, I'm going to dump a little brake cleaner or laquer thinner into my lines and then blow them out with some compressed air. Even using a R134a oil that's compatible with mineral oil, it's important to get the old stuff out. Biggest reason is that the excess oil forms a film on the inside of the tubing in the evaporator and condenser and cuts your heat transfer down a bunch. Excess oil in the system is responsible for as many cooling performance loss problems during conversions as excessive refrigerant charges.
The quote from your local shop for parts is about the same as I paid to get my wife's system (parts and labor) converted last year. They didn't replace the accumulator/drier and they didn't pull the compressor. They used the Castrol conversion kit (costs about $30) which includes the new oil and replacement O-rings. Recovered the old R12, replaced the O-rings, evacuated and charged. It works great. The only reason I'm replacing the accumulator/drier in my 240 is because it's 9 years old. Average useful life of a drier is about 5 years. I'm pulling the compressor and flushing the lines because I love my 240 and I've heard to many stories about "black death".
The Volvo kit, which includes oil, o-rings (although no compressor rings) and a new drier goes for about $80. Not a bad deal. If you go to the 740 FAQ's, you'll find a link to a website where they've posted a copy of the R134a conversion manual. It's a good read.
Oops, sorry. I forgot that your 85 has an expansion valve and a reciever/drier setup. You can't use the VOV. At least it's the rotary compressor, though, instead of the York.
My decision to go with R134a was based on my success with a conversion in my wife's car and my interest in using a VOV. If I had the system you have, I'd:
Remove the compressor, rotate it and dump out any old oil
Flush the evaporator/condenser and lines with laquer thinner
Blow them out with compressed air
Put oil in the compressor, and the condenser and evaporator tubing
Reconnect everything with new o-rings and a new reciever/drier
Pull a vacuum for 30 minutes to get rid of residual moisture
Charge with 32 oz of r134a
or
Get my 609 cert
Buy a two can pack of Autofrost
Pull a 30 min vacuum on the system
Charge it.
Remember, Autofrost has to go into the system as a liquid. Hold the can upside down and "throttle" it into the compressor suction by opening/closing the can tap valve in short bursts.
As far as vacuum pumps go, if you have or can borrow an air compressor, the $25 eductor pump (no motor) from Harbor Freight will do a good enough job. Otherwise, you can pick up a Robinaire pump from a pawn shop for about $75. Or, just call around to your rental places in town. You can rent one for cheap. Harbor Freight has an R12 gauge set for $39. That should get you set up in the wonderful world of A/C repair.
Good luck, man...
Bob Mohr
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