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Suburban Pressure test

thaynie on Mon June 27, 2011 2:21 PM User is offline

Last Fall, i converted my 87 burban to 134. For the conversion, I replaced all hoses with barier hoses, new accumulator, new Delphi Compressor (pancake Type). I flushed both evaporators (Dual Air), flushed all lines and the condensor until flush came out clean. I replaced the orifice tube with a white one. I had my Mechanic charge it for me as i didnt have time or equipment. it worked pretty well, but with it being fall, i didnt really have many HOT days here in Phx. Last week, it stopped cooling. i found that both lines to the condensor had come loose. upon further inspection, the orings had been cut through, thus causing the leak, and loosening connection.

so, I relpaced the orings. put on the vacuum pump, abd a deep vacuum for 1.5 hours. i left the gauges on overnight, and the vacuum held overnight, so was confident the leak was fixed.

so, at this point everything seems good. Its time to recharge the system. the original R12 system takes 5.25# of R12. After reading on this, and other sites, i determine that i need 80 to 90 percent. i split the difference and go for 85%. That means 4.4625 lbs, or 71.4 oz. i figure ok, ill get 6 cans, that 72 ounces, that is still between my 80-90% of R12 value.

At 4 cans into the recharge, Vent temps are at 68 degrees, LS=50, and HS=310. this is with ambient temps at 105-110. I have a big floor fan in front of the condensor, at truck is aidling at 1500. Temp gauge show 190, right where it always is. i continue to add the last two cans, expecting vent temps to decrease. final gauge readings with all 6 cans (72 ounces). LS=55 HS=325. After driving for 15 minutes on the highway, Vent temps are only 58. At lights, stopped vent temps rise to 62. i didnt change out the condensor to a paralell flow, so i know i am losing some efficiency there, but is this the best i can expect from this conversion?

a quick question about Oil. my mechanic uses a synthetic oil made here locally, and uses it in all of his conversions, as well as normal 134 repair work. its is dye tinted, and is called Flouro-dye / retro-lube. i dont remember how much i put into the system, but it was the recommended amount. compresor is quiet, and doesnt vibrate. has anyone else used this Oil, and can recommend for/against it? the label says it is for 134 systems,and is compatible with mineral oil, though i am farely confident i got the old oil completely out before converting.
Comments are welcomed, and appreciated.


JJM on Mon June 27, 2011 5:14 PM User is offline

The 80-90% of original R-12 charge is merely meant as a reference or starting point. Some systems will need more, some will need less. And no, this is far from the best you can expect from the conversion.

With two hungry evaporators to feed with those high ambient temperatures, chances are you're going to need the highest capacity parallel flow condenser you can get in there. You will also probably need to step down your orifice size. Most retrofits work best with a Ford blue 0.067" OT, but you might even consider a red 0.062" or orange 0.057" OT. Once you shrink to OT, higher discharge pressures will likely rear their ugly head.

Is the front evaporator inlet temperature the same as the evaporator outlet (or accumulator) temperature the same, or outlet slightly colder than the inlet? If not, you'll probably need to keep charging, though how much of an effect it will have probably won't be much with the larger OT.

I assume the clutch is not cycling, but the final tweak would be to drop the cut-out pressure on the CPS down to 21-19 PSI.


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thaynie on Mon June 27, 2011 7:36 PM User is offline

i considered changin out the OT to a ford Blue one. i dont want to just vent nearly 90 bucks of 134 to the atmosphere, and have to rebuy. does anyplace rent machines to salvage this 134 so i can reuse it? i havent measured the temp on the Evap input/output lines, as a dont have a thermometer. Can i use one of those laser thermometers, or do i need to tape one to each one of the lines to get best temps?

JJM on Mon June 27, 2011 10:41 PM User is offline

You don't want to vent period at the risk of being terrorized by the EPA. You should have the refrigerant recovered. A local shop might be happy to take it off your hands.

Those pressure readings indicate you're not getting enough sub-cooling, this could be caused by the condenser, OT, or a combination of both. Bottom line is retrofitting is sometimes trial and error. You might get away with just stepping down the OT (but you'll probably have to go to red or orange without a condenser upgrade) but if that doesn't work, now you're out the refrigerant again. My suggestion is replace both the condenser and OT, since almost every retrofit requires a condenser upgrade for proper performance.

Themocouple is the best way to measure inlet and outlet temps. I have a high-end Raytek IR thermometer - remember it was nearly $400 when it came out and I just had to have it - but I never really found it all that impressive. I still find thermocouple to be more accurate. But you don't need either for this quick test, just tell by feel - if the evaporater outlet is warmer than the inlet, the evaporator is probably starved of refrigerant.


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