Apr 29, 2016, 04:55 PM
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Strange Air Conditioning Problem
while lower pressure of r134a boils at a lower temperature, you lose cooling capacity because your evaporator coil which the hot air passes over and where the heat transfer happens is not completely full of boiling r134a to absorb the heat. because of being undercharged, on hotter days the evaporator is less than full of boiling refrigerant and its the boiling of refrigerant when it changes from a liquid to a gas that absorbs the heat. when it's already a gas or vapor in the evaporator it's not taking the heat from the hot air passing over it.
in the orifice tube system on our cars you want the system fully charged and that allows the evaporator to be full of boiling liquid refrigerant and is why there is an accumulator canister prior to the compressor to ensure any and all liquid refrigerant after the evaporator turns to a vapor before reaching the compressor.
in the pic when you are undercharged, there is less blue (liquid) and more white (vapor) in the coils and when that happens you have less than optimum cooling performance. the low side system pressure is really not that important, you cannot go solely by the r134a temperature-pressure chart where r134a at 30 psi boils at 35°F and think that's what your air temp will be out the vents. your low side pressure may be 30 psi but if the evap coil is only 20% full of boiling refrigerant you will have not air out your vents.
Last edited by 1 FMF; Jun 26, 2013 at 01:29 PM.
it does not work strictly on pressure = vent temperature.
while lower pressure of r134a boils at a lower temperature, you lose cooling capacity because your evaporator coil which the hot air passes over and where the heat transfer happens is not completely full of boiling r134a to absorb the heat. because of being undercharged, on hotter days the evaporator is less than full of boiling refrigerant and its the boiling of refrigerant when it changes from a liquid to a gas that absorbs the heat. when it's already a gas or vapor in the evaporator it's not taking the heat from the hot air passing over it.
in the orifice tube system on our cars you want the system fully charged and that allows the evaporator to be full of boiling liquid refrigerant and is why there is an accumulator canister prior to the compressor to ensure any and all liquid refrigerant after the evaporator turns to a vapor before reaching the compressor.
in the pic when you are undercharged, there is less blue (liquid) and more white (vapor) in the coils and when that happens you have less than optimum cooling performance. the low side system pressure is really not that important, you cannot go solely by the r134a temperature-pressure chart where r134a at 30 psi boils at 35°F and think that's what your air temp will be out the vents. your low side pressure may be 30 psi but if the evap coil is only 20% full of boiling refrigerant you will have not air out your vents.
while lower pressure of r134a boils at a lower temperature, you lose cooling capacity because your evaporator coil which the hot air passes over and where the heat transfer happens is not completely full of boiling r134a to absorb the heat. because of being undercharged, on hotter days the evaporator is less than full of boiling refrigerant and its the boiling of refrigerant when it changes from a liquid to a gas that absorbs the heat. when it's already a gas or vapor in the evaporator it's not taking the heat from the hot air passing over it.
in the orifice tube system on our cars you want the system fully charged and that allows the evaporator to be full of boiling liquid refrigerant and is why there is an accumulator canister prior to the compressor to ensure any and all liquid refrigerant after the evaporator turns to a vapor before reaching the compressor.
in the pic when you are undercharged, there is less blue (liquid) and more white (vapor) in the coils and when that happens you have less than optimum cooling performance. the low side system pressure is really not that important, you cannot go solely by the r134a temperature-pressure chart where r134a at 30 psi boils at 35°F and think that's what your air temp will be out the vents. your low side pressure may be 30 psi but if the evap coil is only 20% full of boiling refrigerant you will have not air out your vents.
If theory and real world don't match, then one just has the wrong theory or a missing variable.
Another thing to take in to account is that the air conditioner doesn't just run in the summer. Its a part of the defogger and may be called for in the winter. With lower ambient temperatures, I'd think that a system on the edge would be much more likely to freeze up in those conditions.
Another thing to take in to account is that the air conditioner doesn't just run in the summer. Its a part of the defogger and may be called for in the winter. With lower ambient temperatures, I'd think that a system on the edge would be much more likely to freeze up in those conditions.
OEMS spend hundreds of hours doing critical testing to determine the correct factory refrigerant charge specifications and it is critical. Weigh it in to the OE required charge amount exactly to factory specs and it will be guaranteed to work correctly. If it doesn't at that point then you have a accurate baseline to then begin doing proper diagnostics to figure where the problem lies.
A few ounces one way or the other can make huuuuge difference in cooling performance especially in high ambient temperature conditions.
A few ounces one way or the other can make huuuuge difference in cooling performance especially in high ambient temperature conditions.
