When replacing a bad expansion valve with an after market valve is there a rule or a procedure to correctly set the valve opening?
thanks
H
thanks
H
ac expansion valve setting
- Thread starter bimoverde
- Start date
I’ll try not to get to theoretical with this answer….
In refrigeration systems the setting screw on the expansion valve controls a concept called Superheat which for the end user can be thought of as a safety margin that keeps unboiled refrigerant from going back to the compressor by controlling how aggressively the valve is adding refrigerant to the evaporator. Also importantly it controls the ratio of the temperature of the coldest parts of the system to the temperature of the hottest part (which is the condenser as it’s rejecting the system’s heat).
In the freezer aisle of the grocery store someone has carefully calibrated the high and low side temperatures by turning that screw and measuring the changes.
But in a car it’s rarely used, especially because how do you plan to reach it??
Which brings us to your question, right? Because you have to install yours and commit to that screw’s setting and reassemble the system not having measured anything.
Answer: in the car world those screws are set by the factory assuming a particular refrigerant will be used (usually r-12 or r-134a) and the end user will just have to control the performance of the cooling by adjusting how much refrigerant is put in the system since this will also affect the boiling (evaporating) and condensing temperatures inside the system. Yes, it’s possible that the screw could be set so out of whack that liquid refrigerant goes back to the pistons of the compressor (possibly causing damage) but that’s fairly unlikely. The more likely result of a not-perfect setting is a mismatch of high-side and low-side temperatures according to an optimal engineering scenario. But considering how much variability there is in an automotive setting (think of how much air comes in the front of the car at idle versus 80 miles per hour) it’s kind of a strictly academic point.
If the screw has not been turned since you got it, you’re probably fine just leaving it alone particularly if the valve is advertised as being compatible with the refrigerant you want to use and especially if it’s advertised as having a superheat value of somewhere in the range of 0 to 10 degrees (plus being for the right refrigerant).
In refrigeration systems the setting screw on the expansion valve controls a concept called Superheat which for the end user can be thought of as a safety margin that keeps unboiled refrigerant from going back to the compressor by controlling how aggressively the valve is adding refrigerant to the evaporator. Also importantly it controls the ratio of the temperature of the coldest parts of the system to the temperature of the hottest part (which is the condenser as it’s rejecting the system’s heat).
In the freezer aisle of the grocery store someone has carefully calibrated the high and low side temperatures by turning that screw and measuring the changes.
But in a car it’s rarely used, especially because how do you plan to reach it??
Which brings us to your question, right? Because you have to install yours and commit to that screw’s setting and reassemble the system not having measured anything.
Answer: in the car world those screws are set by the factory assuming a particular refrigerant will be used (usually r-12 or r-134a) and the end user will just have to control the performance of the cooling by adjusting how much refrigerant is put in the system since this will also affect the boiling (evaporating) and condensing temperatures inside the system. Yes, it’s possible that the screw could be set so out of whack that liquid refrigerant goes back to the pistons of the compressor (possibly causing damage) but that’s fairly unlikely. The more likely result of a not-perfect setting is a mismatch of high-side and low-side temperatures according to an optimal engineering scenario. But considering how much variability there is in an automotive setting (think of how much air comes in the front of the car at idle versus 80 miles per hour) it’s kind of a strictly academic point.
If the screw has not been turned since you got it, you’re probably fine just leaving it alone particularly if the valve is advertised as being compatible with the refrigerant you want to use and especially if it’s advertised as having a superheat value of somewhere in the range of 0 to 10 degrees (plus being for the right refrigerant).
excellent information. I greatly appreciate the information you took the time to share with me.
have a great day
Hervé
have a great day
Hervé