Superheat
- Thread starter bearman
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Lefty71
Well-Known Member
Superheat is affected bigtime by both. With a low charge, you aren't utilizing enough refrigerant to flood the evaporator, which is wasteful, and affects user comfort. Overcharge on the other hand, puts too much liquid back to the compressor. You cant compress a liquid, therefore overcharge can damage the compressor in a big hurry. If you are bone dry, its best to weigh in exactly what the engineering called out for your particular vehicle. That's the only way to know for sure. If not, you'll have to use the gauges to calculate the proper charge, which is going to require some experience. HTH, Lefty71
dla4567
Well-Known Member
Cars use a thermal expansion valve (txv) that controls super heat. A/C should be charged to proper subcooling. As Lefty said, it’s best to weigh in charge and check superheated and sub cooling to ensure proper operation.
Thank you both I totally agree with you. So when a aftermarket unit is installed should you add what the factory was set at or should you do what the aftermarket is telling you to put in
I have done a couple of retrofits and done it by temp over pressure and found good results in Phoenix. I get the pressures were they should be from factory then run temps at txv and vent to get superheat. If need be will suck down to get pressures but in order not to be overfull. I try to get evap temp as close to 32 degrees when in engine in cruising range. At idle the swing on txv will jump up a little. Have found out here the need for extra pusher fans have made the job a lot easi
Lefty71
Well-Known Member
Aftermarket meaning just compressor?? I would think you would most certainly charge like they tell you, since original is no longer valid with a different type of compressor. Maybe post a link to the setup you are describing?? So, this is an R134 conversion, as r12 is long gone?? The thing here I think is to remember, that every refrigerant has a different running pressure and boiling point, whether they are newer blends or old standards, therefore if you are following your 196X or 197X service manual for precise information or advice, its going to be R-12 only and not necessarily valid today. HTH, Lefty71
I agree with you for the most part I have doing the compressor change and cleaning out the system putting in new txv etc. Then starting from there but had a little argument that txv didn't need to be change nor did it need to be cleaned out from the r12 oil. He just wanted new compressor put on and add Freon till it was cold inside and that was good for him. Told him not doing that the two oils don't mix and need to have a clean system to work with well he went someplace else.I was happy with that.
dla4567
Well-Known Member
If you don’t know the correct weight of refrigerant, charge to around 10-14 degrees of subcooling. If you have a sight glass that will tell you when you are close (no bubbles). If the txv is working correctly it will control superheat.
I always change txv, filter-drier, flush with r-11x, and vacuum out.
I always change txv, filter-drier, flush with r-11x, and vacuum out.
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Gentlemen,
Superheat is a factor that relates to the evaporator's exit temperature of the refrigerant. Although the refrigerant has evaporated (boiled off and has absorbed heat ... latent heat of vaporization,) because the gas is still cold, it is capable of absorbing additional heat...or superheat. The biggest factor is the calibration of the thermostatic expansion valve (TXV) and the area presented to the air flow (and temperature) in the evaporator. The TXV has a sensing bulb, usually touching the exit line (suction line) of the evaporator so it can regulate the liquid refrigerant entering the evaporator and therefore the superheat. The type of refergant (R12 or R134A) will determine TXV's calibration or operating point and the refrigerant 's specific heat. R134A operates at different pressures compared to R12 so be careful in your application. If the evaporator is flooded (too much refrigerant), you will get liquid refrigerant entering the compressor's suction port which will result in broken valves and severe compressor damage ... owing to the fact that you CANNOT compress a liquid.
Be careful. ..
Bob Renton
Superheat is a factor that relates to the evaporator's exit temperature of the refrigerant. Although the refrigerant has evaporated (boiled off and has absorbed heat ... latent heat of vaporization,) because the gas is still cold, it is capable of absorbing additional heat...or superheat. The biggest factor is the calibration of the thermostatic expansion valve (TXV) and the area presented to the air flow (and temperature) in the evaporator. The TXV has a sensing bulb, usually touching the exit line (suction line) of the evaporator so it can regulate the liquid refrigerant entering the evaporator and therefore the superheat. The type of refergant (R12 or R134A) will determine TXV's calibration or operating point and the refrigerant 's specific heat. R134A operates at different pressures compared to R12 so be careful in your application. If the evaporator is flooded (too much refrigerant), you will get liquid refrigerant entering the compressor's suction port which will result in broken valves and severe compressor damage ... owing to the fact that you CANNOT compress a liquid.
Be careful. ..
Bob Renton
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