converting to 134- how much pressure?

[d9103365]

I've converted two AC systems to 134, and it seems that leaks keep happening...I know our cars are old - and to some extent that's bound to happen...but in a couple cases I replaced most everything...I'm wondering if my mechanic is putting in too much pressure. I believe the pressure or amount of refrigerant changes when switch form r12 to new refrigerant....right? If so, what is the ideal setting? If I'm recharging my system what's the cutoff?

 

[T2R9]

About 80% of the R12 charge.

 

[Demonic]

Oh boy. Typically, the evaporator sizing and flow curve of an R-12 expansion valve are not correct for a 134a conversion. You want to maintain a 35-36* evaporator, or about 33 psi. Most original B body compressors have an evaporator pressure regulator valve. Although the pressure drop spec for the EPR is only 1-4 psi with the expansion valve wide open, it can be too restrictive for 134a. Dart compressors do not use the EPR valve, you can remove it for 134a conversions. It sits in the suction inlet of a RV-2 compressor.

Or if you're not into detailed conversions, just look to maintain about 33-34 psi at 1000 rpm.

 

[PurpleBeeper]

OK, now for a rookie perspective.....I think you still have a leak somewhere. I mean, it's not like the "R-134 pixies" are sneaking into your garage at night to steal your refrigerant.....it has to go somewhere. You need a sniffer or some R-134 with dye in it to find your leak. And then follow the advice above because it sounds pretty darn good.

 

[dla4567]

You can’t charge the a/c based on pressure alone. A lot of factors effect the pressures.
As said above, if you know the original charge of 12, 134 will be approximately 80-85 % of that by weight.
If the liquid line has a sight glass you can charge until the glass is clear (no bubbles).
All leaks will need to be repaired first so a proper evacuation of system can be done before charging.
This isn’t something easily learned by asking a couple questions on a forum.
I recommend seeking help of a professional. (Even then it’s hit or miss). Good luck.

 

[bearman]

lots of different ways to find leaks. must have the equipment for it and once you find it and then switch to 134a are two different jobs. again many different takes on how to convert to 134a so the best thing to do is read everything you can listen to the advice you receive on here. then take what you know talk to couple different a/c shops and move forward. you can also watch some you tube etc. to help understand what your shop will be doing. good luck

 

[d9103365]

Thanks for the advice. I should add that the car was changed over to 134a about 4 years ago. During that time it has blown a new compressor and sprung leaks after long periods of use. Each time it was checked for leaks when maintenanced. The compressor, drier, clutch, and evaporator valve were all replaced as well as some of the hoses. I’m just wondering if it was overcharged hence why it may have been blowing components.

 

[bearman]

how is the condenser cooled by factory fan or aftermarket. were the pressure switches changed out also and what is cut in pressure and cut out pressure.

 

[oldbee]

Overcharge is a possibility, but the press.relief valve should open & vent the excess. No oily spots anywhere(?) indicating a leak?

 

[Lefty71]

R-134a cannot be contained by hoses. Has to be all steel (metal) with a refrigerant blend like that. Not the same as the properties for r12 at all. Read up on "barrier" hoses and "permeation". Refrigerant must be weighed in to the amount the system was engineered to use (consult manufacturer recommendations for the new eq.). Do not try to charge by "running" pressures. HTH, Lefty71

 

[dan juhasz]

I concur with lefty, 134a molecules are smaller and will seep thru r12 hoses. Need to use barrier hose.
2. Almost a must to have an electric fan to maintain workable high side pressures. No fan and high side pressures will go to 350 /400 psi in traffic without air flow. This puts a heavy strain on the compressor and hoses etc. People will disagree but 134a conversions without a fan, a modern condenser and a modern compressor just don't work well.

 

[bearman]

there is mixed feelings about extra fan for cooling. i agree that the extra fan is a big help but control of heat over pressure really becomes a issue. most a/c folks like to see a 30 degree drop in temp across the condenser. which is best so when it get to the expansion valve and then hits the evap coolness is already happening. the extra fan gives you the help to get it cooled down well don't forget about the cutout switch what pressure is it set at. you can have the clutch cycle more or less depends on what you're after. i like the extra fan and also like the control of switches on the low and high side. adjustable expansion valves also a great help.

 

[5.7 hemi]

Ambient temperature has to be taken into account when charging.