Engine Size: 2.5
Refrigerant Type: R12
Ambient Temp: 90
Pressure Low: 0
Pressure High: 0
Country of Origin: United States
I have been off the forum for a while, as all my AC efforts from the past are working great thanks to the help I received from this forum.
Being a glutton for punishment, I recently acquired a 944 from my brother in law. The car has factory AC and uses R12. I am told the AC "doesn't work" which is true. The question is: why is it not working? I have no background info to work with so I have to start from scratch.
So my question to the group: how should I proceed? What testing should I do and in what sequence? I believe it would be best to leave this car with R12 if possible.
I agree to keep it R-12, available and legal to use.
First thing is find out why it's not working. I assume that it blows air, but not cold (if doesn't blow, then electrical issue). Second likely is out of refrigerant, would be to add some refrigerant (even R134a for test purposes) and find where the system is leaking and correct the leak.
I use 134a all the time for leak testing r-12 systems...just make sure you don't run the compressor while the 134a is in there. A small amount of 134a, then pressurize the rest (I go to about 100 psi, 120 max) with nitrogen.
If you use an electronic leak detector, be aware that brake cleaner or similar items you may have used to clean off connections, etc will set it off for at least several days.
Wondering if pressurizing a bit with nitrogen then lathering up with big blue might be useful? Where might a DIY'er like me acquire a nitrogen source?
During the pressure test, you put in just a trace amount of 134a (like 1/2 oz or less) for the leak detector to pick up. The vast majority of what's in there is nitrogen.
Yes, lathering up with big blue should help as well.
I picked up a nitrogen tank from the local welding supply where you trade in your oxygen or acetylene tanks. I expect it'll last me the rest of my life. Need a regulator for it as well of course.
Edited: Thu July 25, 2013 at 2:53 PM by webbch
A little confused about the compatibility of mineral oil and PAG when upgrading to R-134A. I read this official document from Porsche on how to proceed:
If I am reading correctly, the procedure is to remove at least half of the old oil that is in the system, than adding the Denso equivalent of PAG 46. This makes it sound to me as though it is not the worst thing in the world to have residual mineral oil in the system.
Looking forward to hearing from these wise ranks.
For leak testing, use a trace of R134a and N2. Use about 100psi of pressure. After you find the leak, just vent the mixture. Recharge with r12 for best results. If you decide to usde R134a, you'll need to get almost all of the mineral oil out, flushing properly with the proper equipment is important. Then use Bava 100 oil. I would keep this vehicle R12 if at all possible.
Don't want to highjack this thread but when N2 is mentioned for pressure testing, I have to think about it would cost for a tank(whatever size) and a regulator, etc. for use.
Small tanks of N2 are cheap from your local gas supply house; and an Oxygen regulator is cheaper than an N2 regulator, which works just fine for this type work.
Airgas does retail.
TRB stated that small tanks of N2 are cheap. Not sure what he calls cheap? I just looked up empty nitrogen tanks, a 40cf was just under $200 plus you need a regulator on top of that.
When I decided to pressure test my A/C with nitrogen gas, I checked Craigslist for a tank. A 125 cu. ft. tank with a DruVa regulator was on sale for $80. I exchanged the empty tank for a full tank at Airgas. It cost me $30 plus tax and fees.
They are cheap in the overall picture.
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