Question for the A/C guys???

[MY90GT]

Just did a total conversion (all new parts) from R-12 to R-134a.
Had the A/C shop put a charge on it last night. It did fine last night
and this morning. High 70's, Went out today, low 90's, and as I was
driving down the road, the high pressure pop off valve on the A/C blew
some oil and freon. It still feels like it's cooling pretty well, even in the
heat. Could they have just over charged it. And if it doesn't do it again
should I worry about it. Do the pop off valves ever go bad?

 

[jrichker]

I would have them put the charging gauges on it to check it out. Maybe they overcharged it.

There is a label under the hood that specifies the amount of the refrigerant charge. You charge 134a systems to 80%-85% of what the R12 charge was. For a system that held 42 oz of R12, the proper charge is about 32 oz of R134a.

Air left in the system, a result of it not being vacuumed down properly will also cause high discharge presures.

 

[MY90GT]

The original R-12 system called for 41 oz. of freon. They installed 36oz of R-134a, which sounds about right. It seemed to cool fine, but honestly it seems to cool better, after it blew some off. Today is was 91 and high humidity. After driving the car for about 10 minutes, Max A/C blower on high, the air temp. in the car, passanger seat was about 82, discharge temp at the vent was 51. So I'm getting about a 30 degree drop.

 

[PuterAmI]

Actually, the system you have MY90GT calls for 41 ounces total charge. This is to include oil. A system should have 8 ounces of oil. In a proper conversion, the oil is flushed out of a system and the proper amount of new oil is installed before charging the gas. Did you do this?

Then, you subtract the amount of oil from the total and that gets you to where you should be for the gas. So, yes, you were way overcharged at 36 ounces.

I am not the shop, but the way I would fix this is to set the engine at about 1800 RPM for a few minutes to get the system to stabilize, then bleed it off until I get low side pressure at about 20-25PSI and the high side ~225-250PSI, then watch the vent temp. You should be able to get it down to the 38... maybe even 35 degree range. Did you adjust your LPCS? It needs to be dropped from the 25PSI for R12 to somewhere about 18-21 depending on what works best for you.

I graduated Eastern in Middletown.

 

[MY90GT]

The entire system was changed out. I didn't use any of the old parts, except the suction and discharge manifold, since they didn't come with the new compressor. Yes I added 8 ounces of Ester 100 oil. If the LPCS is the low pressure clutch switch, I installed one for R-134, the lower PSI.
Once again, if you want something done right, you need to do it yourself!!!!

 

[GearHd6]

I was wondering what it cost to have the A/C converted to R134? I need it done to a 91. All the parts are there and it used to work with the R12 but now its out of charge.

 

[Fett]

Yes I added 8 ounces of Ester 100 oil.

I thought Ester oil was for R12 only, where as PAG oil is for R134? Not sure if that matters, but I thought that was the case.

As far as changing an R12 system over to R134, that is easy and cheap. Any autoparts store will sell a retro fit kit, which consists of both high and low side sharging port adapters, and some oil. Flush the system out and vac it VERY well, add the oil to the compressor, screw on the fittings, and fill with freon.

 

[redfox91]

The truth is it really doesnt matter I have a 91 and about 5 years ago I had to change my compressor so instead of r12 I went back with r134 Auto parts store has a cheap 30 dollar conversion kit i changed nothing but the compressor and fittings and mine still blows cold to this day with no leaks or problems...

 

[PuterAmI]

Mineral oil is for R12. Ester (POE) and PAG are for R134A. Ester oil is compatible with mineral oil where PAG is not.

The cost varies to convert it properly. Do it yourself with new parts for a little over $200.

 

[87'GTstang]

I would have them put the charging gauges on it to check it out. Maybe they overcharged it.

There is a label under the hood that specifies the amount of the refrigerant charge. You charge 134a systems to 80%-85% of what the R12 charge was. For a system that held 42 oz of R12, the proper charge is about 32 oz of R134a.

Air left in the system, a result of it not being vacuumed down properly will also cause high discharge presures.

Couldn't agree with it anymore. R134 indeed does need less refrigerant than the r12.

 

[Andres2882]

Anyone have a link or something for the A/C swap? Want to do that myself after 5 years of no A/C in sunny Fla. BTW, you're not a man till you ride around A/C-less for 5 years, or wait, maybe your just a sweaty man.

 

[PoopDawg]

Anyone have a link or something for the A/C swap? Want to do that myself after 5 years of no A/C in sunny Fla. BTW, you're not a man till you ride around A/C-less for 5 years, or wait, maybe your just a sweaty man.

LOL! I hear ya! I've NEVER had a car with A/C until TODAY.. Just got it all fixed up and converted to R-134a. it's sooooo nice! FL+no a/c = HELL After 8 years with no a/c... I much appreciate it now!

Nick

 

[PuterAmI]

Anyone have a link or something for the A/C swap?

http://www.veryuseful.com/mustang/tech/general/R12-to-R134A-Conversion.html

 

[MY90GT]

When they charged the system, they put the quick connect fitting on. I have
gauges but had to order the female quick connect fitting which should be in any day. We have had really hot weather here 95-105 the last couple of weeks, so
it's hard to tell how well it's working. At least I stay comfortable now.
As far as the conversion, I replaced EVERYTHING, so I didn't have to worry about any problems hiding on me. If you don't want to go through that expense, then at least pull the compressor off the car and flush it really good with mineral spirits.
Then flush everything else with mineral spirits, and blow it out. I would change the suction line hose with the accumulator, it's what traps all the moisture and crap in you system. Reinstall the compressor, add 8oz. oil, then vacuum it down and charge it. Pulling a vacuum does NOT remove the oil in the system.
Like the guys said, take into consideration the 8oz. of oil when figuring how much Freon to add. They didn't at the shop and overcharged my system. While I was driving it the other day, the high head pressure valve popped and released some Freon. It actually cools better now.