sam12345

iTrader: (1)

I have noticed on all my cars (they all have the expansion valve system) that when the outside ambient temp is cooler (70 to 80 F) the duct temp is higher (48 to 50 F) than when the ambient temp is warmer ( 90 to 100 F) the duct temperure is cooler (40 to 44 F) I am talking about the duct air temperature not the cabin air temperature. This is with the temp of the controls set to its lowest temp and fan on medium.

It seems counterintuitive. Is this because the txt valve (expansion valve) is preventing the evaporator from freezing and the warmer inside cabin air allows the evaporator to run cooler?

I still don't understand why this is can somebody enlighten me? But I see this on all my car (4 of them)

fixmiester

I believe you are thinking on the right track. As I recall, most exp valves require a five degree delta across them before they will open. During cooler ambient temps, the valve is open for a pretty short duty cycle, before it closes again, resulting in a relatively higher plenum temp. Under higher heat loading and cabin temps, it stays open longer, even continuously, allowing the full flash of all the freon the compressor can deliver, which really chills the plenum air. The freeze sensor will turn the compressor off, if the blower isn't delivering enough cabin heat load to keep the evap. above 34 degrees, or so.

sam12345

iTrader: (1)

Thanks, I thought it was something along those lines