DanG144
Top Post Dawg
My AC system was not providing full cooling anymore, and I suspected I needed a new Refrigerant Control Valve, RCV. This valve is a simple spring loaded pressure control valve inside the Sanden SD7V16 compressor. I have changed out more than a dozen for friends and family, and it looked as if it was my turn.
The purpose of the RCV is to control the suction pressure of the compressor high enough such that the evaporator will not freeze up, but low enough to give you full cooling.
The pressure in the evaporator will be slightly higher than the suction pressure inside the compressor, so you can stand for the pressure to be as low as about 25 psig (29 degrees F). I seem to remember that the Bentley suggested 35 psig (40 degrees F), but I consider this too low. I would want a minimum pressure of 25 psig(29F) and a maximum pressure of 30 psig (35F).
The replacement RCVs come from China, and I find their setpoints vary quite a bit, from a low of 25 psig to a high of 33 psig. I don't have a way to test them on the bench, and I really don't know what their true differential pressure setting is; I am reporting the system operating pressure that results.
Because I am as curious as a cat, I wanted to see what my system would operate at with the RCV bypassed. In an article that I have shared before a mechanic from Mexico points out how to bypass the RCV function by replacing it with a bolt. I decided to just remove the O-ring that separates the high and low pressure sides of the RCV to see what resulted.
At idle on a 100 degree South Carolina day, with normal (very high) relative humidity, the sytem at idle would maintain 35 psig, and about 43 F air outlet temperature. So even with the compressor at full displacement, full load, this is the best it could do.
But during a short (5 minute) interstate drive in my 5 spd, the outlet air temperature, with the cabin fan at full speed dropped to 23F!!
Continued operation at this condition will result in a ball of ice at the evaporator, but it sure felt good.
I replaced my RCV and the O-ring and got one that operates on the high end of the band, unfortunately, but still much better than the old one.
The purpose of the RCV is to control the suction pressure of the compressor high enough such that the evaporator will not freeze up, but low enough to give you full cooling.
The pressure in the evaporator will be slightly higher than the suction pressure inside the compressor, so you can stand for the pressure to be as low as about 25 psig (29 degrees F). I seem to remember that the Bentley suggested 35 psig (40 degrees F), but I consider this too low. I would want a minimum pressure of 25 psig(29F) and a maximum pressure of 30 psig (35F).
The replacement RCVs come from China, and I find their setpoints vary quite a bit, from a low of 25 psig to a high of 33 psig. I don't have a way to test them on the bench, and I really don't know what their true differential pressure setting is; I am reporting the system operating pressure that results.
Because I am as curious as a cat, I wanted to see what my system would operate at with the RCV bypassed. In an article that I have shared before a mechanic from Mexico points out how to bypass the RCV function by replacing it with a bolt. I decided to just remove the O-ring that separates the high and low pressure sides of the RCV to see what resulted.
At idle on a 100 degree South Carolina day, with normal (very high) relative humidity, the sytem at idle would maintain 35 psig, and about 43 F air outlet temperature. So even with the compressor at full displacement, full load, this is the best it could do.
But during a short (5 minute) interstate drive in my 5 spd, the outlet air temperature, with the cabin fan at full speed dropped to 23F!!
Continued operation at this condition will result in a ball of ice at the evaporator, but it sure felt good.
I replaced my RCV and the O-ring and got one that operates on the high end of the band, unfortunately, but still much better than the old one.