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Old 11-19-2013, 01:24 AM
Pants Pants is offline
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Join Date: Nov 2013
Location: Honolulu
Posts: 47
1983 300SD A/C rejuvenation process?

The second owner of my recently-purchased 1983 SD was, shall we say, not concerned with full disclosure in all areas, and an outright liar about others. The realm I have in mind right now is A/C. About this, he wrote:
A/C works fine and was professionally converted. The system was converted from R12 to R134a by dumping the mineral oil from a new compressor before it was replaced and refilling with synthetic Esther oil. Barier hose was used where needed but most of the lines are metallic. At idle you will not feel the air cool quickly because the boiling point for the R134a is > (higher) than R12. It has been sitting since May and the tollerances on the fittings are not like modern systems so they need to stay wet with the Esther oil (I believe the R134a molecule is smaller than R12) or you have to add R134a at the blue covered, R134a, nipple. (correct me if you know otherwise)
So on the one hand, he wasn't really claiming expertise, but on the other, he's pretty specific about what was done (even if subtly implying that he'd had the work done himself, though receipts prove otherwise.) 1st owner was fairly responsible, it appears from records found in the car. Receipts show he had one shop recharge with R134a (and two days later, another shop checking it to find out what was [still] wrong, I infer leaking) in early 2007. When I test-drove the car (11/2013), entirely on base with installation speed limit of 25 to 30, I detected no A/C.

After hot-wiring the compressor-clutch for a few minutes and getting no evidence of cooling, I verified/discovered that there was virtually no refrigerant in the system - just a puff from the low-side Schrader valve, residual from my own ill-fated attempt to charge without the compressor operating. The compressor isn't noisy. I separate the hoses from it briefly in order to see if any obvious nasty crud came out, and only got dye/some clean-looking oil drops out.

Other observations:
  • no low-pressure cutout switch existed; the leads had been jumped with a new-looking clean wire: I think 2nd owner was shotgunning to try to fix, and gave up.
  • Despite that jumper, other electrical issues (that I will get into in later diagnosis) keep the clutch from ever getting power, short of my providing a hot-lead for my test as mentioned above.
  • There's an unknown dry very-black stain from something near the evaporator (mostly in air-duct above driver's knees, it weeped out near the right edge and stained the carpet a little there)

My plan goes something like this - please critique:
  1. replace accumulator, with new LP cutout and aux fan switches
  2. replace all o-rings but keep existing hoses (no obvious decrepitude there...)
  3. replace expansion-valve - err, that's if someone will tell me it's not an all-day ***** of an affair (?...I've looked at it, and though not a piece of cake, it doesn't look horribly hard)
  4. pressure-test with Argon (it's what I've got handy) to 200psi max - hold for...an hour? a day?
  5. on passing P-test above, evacuate and recharge with R134a (and add oil?)

Should I flush?
Part of me really wants to know about pros/cons of flushing out the whole system, in order both to clean out whatever's there, see if any metal comes out, and to start with a known oil type/qty.
  1. Is that feasible with cobbled-up equipment, i.e. something like compressed air and a means to blow through a flushing agent? (I'm thinking a siphon-gun, say)
  2. Is it advisable?
  3. If I do this, can I add a full charge of oil to low-pressure Schrader valve port?

Been-there-done-that responses welcome.

Mahalo - Dave
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