R-134a vs. R-12 capacities
#2515292
06/30/18 02:34 PM
06/30/18 02:34 PM
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340clone
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I am retrofitting my '74 Charger with factory air to R134. I have two cans in the system in the car, and it seems to blow cool at idle. I haven't taken it on the road to see if it will blow colder when moving.
I am concerned about adding too much 134, as I've read that only 60-80% of R-12 capacity is required before efficiency starts to drop. So how many cans of 134 should this system take? Anyone have any experiences or thoughts? Thanks!
Last edited by 340clone; 06/30/18 02:34 PM.
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Re: R-134a vs. R-12 capacities
[Re: Supercuda]
#2515296
06/30/18 02:41 PM
06/30/18 02:41 PM
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GMP440
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No more than 80% of the R-12 capacity. As mentioned by the previous post there is a conversion chart online that will give you pressure readings for different temperatures. Keep in mind the R-12 systems can not handle high pressures.
Last edited by GMP440; 06/30/18 02:44 PM.
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Re: R-134a vs. R-12 capacities
[Re: 340clone]
#2515525
06/30/18 08:09 PM
06/30/18 08:09 PM
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That's why converted systems don't work very well either
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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Re: R-134a vs. R-12 capacities
[Re: 340clone]
#2515552
06/30/18 08:49 PM
06/30/18 08:49 PM
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Guitar Jones
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You need an R134a specific condenser. Also the converted systems work much better with good air flow across the condenser. Electric fans help to keep the high side pressure down when sitting in traffic. Expansion/H valves are different too.
"Follow me the wise man said, but he walked behind"
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion. '74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Rear disc and hydroboost coming soon! 2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
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Re: R-134a vs. R-12 capacities
[Re: 340clone]
#2515928
07/01/18 04:51 PM
07/01/18 04:51 PM
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340clone
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OK, so at about 90 degrees outside with about 60% humidity I'm getting about 55 psi on the low side. I didn't even hook up high side. It's comfortable in the car but I wouldn't say it's freezing me out. This was also at idle, so I imagine it will help when more air is going across that condenser. This is with 24 oz. of 134 in the system.
Just wanted to post my findings. Any advice and thoughts welcome!
Last edited by 340clone; 07/01/18 04:51 PM.
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Re: R-134a vs. R-12 capacities
[Re: 340clone]
#2515932
07/01/18 04:57 PM
07/01/18 04:57 PM
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I like to shoot for 38 degrees at the center vent
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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Re: R-134a vs. R-12 capacities
[Re: 340clone]
#2516171
07/02/18 12:12 AM
07/02/18 12:12 AM
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GMP440
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The pressures look ok. What is the temperature at the a/c vents? Keep in mind on these R-12 to R-134 conversions you just don't get that freezing you out of the car effect like you get with the old R-12 gases. How does the a/c system feel when driving the car? If you have a fan, face it to the grill so cool air is blown against the condenser. Sit in the car and feel how cold it is. Also, check the pressure while you do this and record the pressures. See what the differences are. Forgot to ask; was the system evacuated before charging with freon?
Last edited by GMP440; 07/02/18 12:44 AM.
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Re: R-134a vs. R-12 capacities
[Re: 340clone]
#2516181
07/02/18 12:30 AM
07/02/18 12:30 AM
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383man
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I have changed many newer (1980 and 1995) cars over to 134 and as far as I remember all of them worked fine. I changed my 86 Aries K- car I used to have and I did not do much to it to change it over. At first they said you had to change a lot and now today you can just empty the R12 and pull the system down and add the right oil and then add the 134. That's about all the kits give you today. Heck when they first started to change some we got a 5 page manual on all the things they said to change including the compressor and drier or suction accumulator. I have used the kits of today and changed no hard parts at all and had the systems work fine. Course I have not don't any 60's or 70's cars that used the EPR valve and V comp. One thing I also notice is the 134 will get pretty cold but it usually takes longer to get real cold the the R12 system did. Ron
Last edited by 383man; 07/02/18 12:33 AM.
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Re: R-134a vs. R-12 capacities
[Re: GMP440]
#2516223
07/02/18 02:03 AM
07/02/18 02:03 AM
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340clone
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The pressures look ok. What is the temperature at the a/c vents? Keep in mind on these R-12 to R-134 conversions you just don't get that freezing you out of the car effect like you get with the old R-12 gases. How does the a/c system feel when driving the car? If you have a fan, face it to the grill so cool air is blown against the condenser. Sit in the car and feel how cold it is. Also, check the pressure while you do this and record the pressures. See what the differences are. Forgot to ask; was the system evacuated before charging with freon? I couldn't get an accurate reading with my IR thermometer, and I don't have a vent thermometer so I'm not sure wnat vent temp is. Haven't driven it yet but feels comfy, but not freezing cold at idle. (Being close to 95 degrees here in Louisiana doesn't help much!) Will need to drive it, but good idea about the fan. I will also try that. System was rebuilt about 10 years ago but never filled. I sold the car then, and recently bought back from guy I sold it to. He never filled either. Rebuilt compressor, new evap, new hoses, bought new filter/drier this week. Condenser was not replaced, but removed and thoroughly flushed with lacquer thinner. I probably should have gone back with R-12, but since I didn't have any and since I thought I had a good clean slate I'd go with R-134. I do have some Freeze-12, but I hear it's mostly R-134 anyway and like R-12 it's so expensive if you ever need to add cans...
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Re: R-134a vs. R-12 capacities
[Re: 340clone]
#2516232
07/02/18 02:39 AM
07/02/18 02:39 AM
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340clone
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After reading about EPR valves, etc. I'm now wondering if I'm going to have problems since mine was not removed? What exactly will happen if EPR remains?
Also wondering now if I should evacuate system again and drop in Freeze-12? Would I have to flush all or part of system? BTW, I filled the system with about 7-8 oz. of Ester oil before I added the R-134. They say that Ester is compatible with either 12 or 134 oils. So what about the oil that was in the 2 cans of 134? Would this cause a problem if I went back to Freeze-12? Or, maybe I should just let it fly as is?
Thanks for any and all help! Sorry for all of the questions. Not really well versed in auto a/c and no one wants to fool with anything this old around here.
Last edited by 340clone; 07/02/18 12:41 PM.
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Re: R-134a vs. R-12 capacities
[Re: 340clone]
#2516402
07/02/18 02:43 PM
07/02/18 02:43 PM
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Joined: Jan 2003
Posts: 27,421 Balt. Md
383man
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After reading about EPR valves, etc. I'm now wondering if I'm going to have problems since mine was not removed? What exactly will happen if EPR remains?
Also wondering now if I should evacuate system again and drop in Freeze-12? Would I have to flush all or part of system? BTW, I filled the system with about 7-8 oz. of Ester oil before I added the R-134. They say that Ester is compatible with either 12 or 134 oils. So what about the oil that was in the 2 cans of 134? Would this cause a problem if I went back to Freeze-12? Or, maybe I should just let it fly as is?
Thanks for any and all help! Sorry for all of the questions. Not really well versed in auto a/c and no one wants to fool with anything this old around here.
The EPR valve is the evaporator pressure regulator valve. Basically it controls the evaporator pressures so it don't freeze up. In AC systems the pressures work right with the temps of it. Lower pressure in the AC system means lower (colder) temps and vice versa. In other words if the evap press gets to low for to long and hangs below about 28 psi the evap can start freezing up on the fins. Keep the evap press about 32 and slightly above and you get cold temps and no freezing evap. The Fords and GM cars used the same type of valve that they called the Suction Throttle Valve. Most all newer cars have gone away from that system and have gone to cycling compressors to control evap freezing which will turn the comp off if the evap press gets to low and the newest cars may also use variable displacement compressors to control evap freeze up. Some also went away from the exspansion valves to Orfice tubes to control Freon flow to the evap and control the high to low pressure sides. I will admit that all the cars I have switched from R12 to R134 were a bit newer then the cars that used the EPR valve as most or all the ones I have changed were cycling systems that cycled the comp on and off to control evap pressures. So I cant tell you how the R134 acts in that system but some of the others on here seem to have changed that older system and might help you. Good luck with it. Ron
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