R-12 to R-152a Conversion

[Arved]

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,

[Tayters]

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!

[Arved]

aTdHvAaNnKcSe - ha, cryptic.

It's an oldie from the days of usenet. :-)

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

Thanks! Yeah, that helps a lot. More than the dozens of Youtube videos on this.

65psi equates to 22*C ambient so would that be about right for your standing pressure?

Yes. Makes sense now.

Would appear to be a bit short of charge from your description. How much did you put in?

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.

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!

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