rcrone928

OK I'm rebuilding my ac on 83 928. I have good used compressor plus new o rings drier and exspansion valve. I plan to convert to r134a, so here[s my confusion.. I've read alot of posts about ac on this list and not getting any idea if i should be useing ester oil or, PAG46. I went to alocal ac shop and told them what i was doing and they said they only use pag oil. I thought ester was less likely to jell if there is still r12 or mineral oil left in the system. any one have a strait answer about this I would be very relieved. Thanks to all.

jwillman

I just did this as well. If you are reusing any componenets that have previously used R12 and mineral oil you want to use Ester oil. I installed a good used oumo and there is no way to get the all the old oil out. Ester oil was confirmed by Dan and Dr. Bob as the correct choice. Search my name for the recent posts.

Calgary Ole

I put in ester oil. You need to put in the correct amount for your system.

Ducman82

i used PAG, being the system was converted before. the new compressor i got has Mineral onil (r12) so i had to drain it and re fill with PAG

blown 87

A kitten was just killed for some one thinking of converting to 134A.

WallyP

If the system has had R-12, you must use POE oil.

rcrone928

Thanks for the quick replies! I know r12 would be the best way to go but @56$ a pound for r12 its' robbery. If I go with 134a I can get it anytime at an auto store. It sure is great to have such help on this web site. I just wish I had knowledge to share with you guys about these cars. I hope no one kills any kittys because of me..

dr bob

Greg, if you like ice in your Jack, I can make some for you with my R-134a-converted system. Black car, 2000RPM cruise on a 90º+ SoCal day, 19º center vent temp. In the words of that great bird watcher Audubon: "It's pretty falcon cold!"

blown 87

Try that jumpered freeze switch in Atlanta and get back to me once your evap core thaws out.

And look at the pressures on the high side when sitting in Atlanta traffic on a 100 degree day.

I have seen them blow the safety plugs out before.

rcrone928

What plugs?. I never get stuck in traffic out here in Arizona. Also no moisture in the air to freez anyway.

blown 87

Safety valve, burst plug, pretty much all compressors have a safety of some sort.

No traffic and no moisture, sounds good.

dprantl

I keep hearing shops that use only PAG oil in R134a conversions? Jeez, it's no wonder there are so many crap conversions and people keep complaining about R134a system performance...

Oh, and no need for thawing here in Atlanta, it's nice that the freeze switch is adjustable.

Dan
'91 928GT S/C 475hp/460lb.ft

WallyP

R-134a is $16-$17 at the auto parts stores here, and $8 at Big Lots...

dr bob

There's a very good reason why I recommend that folks use a combo safety switch in their conversions. The high-pressure compressor cut-out is a good idea, rather than depending on the safety plugs in the compressor (don't remember seeing any...) or the drier.

On the freeze switch jumper-- Here in the coastal desert climate in Los Angeles, humidity is low enough that it takes an hour of driving to ice over the evaporator. On extended trips I either pull the jumper or plan on manually cycling the compressor off when I notice airflow falling off. The 'cool' thing is that the ice in there still provides a bit of cooling as it thaws.

The low humidity here is also a big reason why the evap temps can get so low. Condensing moisture from the incoming air sucks a lot of capacity that would otherwise be available for cooling the air. This shows up in systems that seem to only have center vent temps in the 40's and 50's, even with correct pressures. The system uses all its capacity to get the air temp down to the dew point. Dew point is the temp at which the relative humidity of the discharge air is greater than 100%, where the partial pressure of the entrained water vapor is higher than the actual barometric pressure. The water changes from vapor to liquid, a process that sucks up somewhere in the neighborhood of 1000 BTU's of system capacity for every pound of water condensed. That 1000 BTU's doesn't change the air temp, it's all spent on the state change of the water. Of course the drier air coming into the cabin feels cooler on the skin, since it can evaporate perspiration. How cool does it feel? Somewhere in the 5-10 degree range above that dew point temperature. "Max AC" setting on most car systems blocks the incoming air so the system can condense out the moisture in the cabin, ultimately getting the interior humidity low enough that there's available capacity to cool the air below the dew point temperature.

Forty-some years ago, I left the east coast for SoCal. My mission was to go to the relatively free for residents UC schools. The dry climate here was such a blessed relief from the summer heat and humidity that I forgot to move back. I still visit for work projects, and I love the people and the cultures, but it will be a cool, dry day in hell (literally) before I move back voluntarily.

blown 87

The South is a wonderful place to live, it would almost be perfect if you could not fry a egg on the pavement 9 months out of the year.
It is all ready 75 here at noon, and will be over 90 by days end, with who knows how much water in the air.