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Thread: R-12 to R-152a Conversion
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28-04-2014, 02:46 PM #1
R-12 to R-152a Conversion
I have a 1994 Toyota pickup (Hi-Lux out of the US) that has had inoperative A/C since I bought the truck 15 years ago. I've finally decided to find what's broke and fix it as I convert it to something other than R12.
While R-134a is a common conversion, I found some information on alternatives. Among the alternatives, R-152a (a.k.a. "Dust Off") raised its head as an alternative. So I threw caution to the wind and said "what the heck" and tried it this weekend.
I had some trouble finding specific information about this conversion. I'm real interested in finding out what pressures I should expect to see in my system. Here's my experience, but note that this is from a highly suspect system:
1. High pressure seems to be a steady 100 psi. Running or not. This seems a bit low compared to R-134a systems I've dealt with in the past.
(this is where it gets strange):
2. While charging (from a vacuum), low pressure side would not get above 15 psi.
3. As soon as I shut off the R-152 supply, the low pressure side would drop to 15 in. Hg Vacuum. The pump would not shut off (so I suspect a bad pressure switch controling the compressor clutch).
4. When I turn off the engine, the LP side would rise to 65 psi. This seems way high.
5. Absolutely no cooling at the vent. 90F day, 95F+ vent temp with A/C on high and recirculating.
Any information on R-152 and the expected pressures would be helpful. Any help in diagnosing my colling system based on the above would also be appreciated.
aTdHvAaNnKcSe,
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28-04-2014, 09:07 PM #2
Re: R-12 to R-152a Conversion
aTdHvAaNnKcSe - ha, cryptic.
Never herd of the stuff but came across this:
Case Study: http://www.sae.org/altrefrigerant/pr...presw-hill.pdf
Pressure/Temperature Chart: http://www.hvacsuitemobile.com/HVACS...a_TP_chart.pdf
65psi equates to 22*C ambient so would that be about right for your standing pressure?
Would appear to be a bit short of charge from your description. How much did you put in?
Either that or there is a restriction/blockage and when you turn the system off it equalises through the compressor. Don't know if that could happen mind...
ChANeDerYs!Health and safety first..........unless I'm in a hurry.
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05-05-2014, 04:57 PM #3
Re: R-12 to R-152a Conversion
It's an oldie from the days of usenet. :-)
Thanks! Yeah, that helps a lot. More than the dozens of Youtube videos on this.
Yes. Makes sense now.
I couldn't weigh the can, but less (I'd say much less) than a 10 oz. can. Given the ratio of the molecular weights between R-12 and R-152a (120.9 g/mol vs. 66.05 g/mol), I couldn't get a full charge. I'm still scratching my head how I can have 15 inches of vacuum, and no flow from the can to the manifold guage set. I've used this set to charge a more modern car with R-134a, and, as shown with the 65 psi with the engine off, some r-152a got into the system, so there's no blockage between in the charge line (or can tap). But a blockage in the Toyota's A/C system? After 15+ years without use, anything is possible.
Time to open everything up and (at a minimum) blow things out. It will give me an opportunity to go through the system and replace O-rings, clean things out, and replace the oil.
Thanks again,
- Arved