Re: Vacation Car - 56 Patrician
Posted by HH56 On 2021/8/10 10:17:45
The original expansion valve had a small port on the suction side tube out of the evaporator for the sensing. That is the top tube in this photo where you can see the small hole on the side of the fitting. The bottom photo shows the expansion valve with the sensing connection to the top tube.
It will be interesting to know how it works out if they are planning to use the modulator valve for temp control. That was the control method using the obsolete hot gas bypass system for temp control where refrigerant is short circuited around the evaporator to maintain the pressure in the evaporator at a set point. Presure in the evaporator is directly related to temperature so the valve monitors the pressure to bypass the refrigerant. No idea if the Packard valve can be adjusted for the different pressures when R134a is in the system.
There were several temp control methods used back in the day and gas bypass was just one of them that remained popular until something better (AKA less costly) came along. I think by the late 60s that method was gone on most cars. For many years it was only the less expensive hang on AC units that used cycling clutch but now almost everything has gone that way because it is cheap to implement and reliable. Also helps on the gas mileage number when you can turn the compressor off for a few minutes. Downside is when the compressor cuts off the evaporator warms and you get that muggy feeling when it blows moist air for a few minutes until the compressor starts and cools the evaporator so it starts dehumidifying again.
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