I think the superheat is in degrees F, because I see some expansion valves on Rockauto that are 8 to 10. No way those numbers are C, that would be too much superheat.
I have not performed superheat measurements myself. So just repeating what I think I understood....at a typical 35 psi on the low side, the refrigerant temperature should be 40 F (or 4.4 C. See pressure-temperature chart below). And with an expansion valve of -1.5 F then, the temperature of the pipe out the expansion valve should be 40 - 1.5 = 38.5 F.
If the superheat is higher than specified, then less of the evaporator is flooded with liquid refrigerant, and the cooling will suffer.
Anyway your evaporator is no where near that cold. I do not know why, as there can be many reasons, including heater air leaking into the cold side, etc.
On an expansion valve system, the expansion valve superheat is set at factory, so I do not look at them when things are working. The supercooling of the condenser can be used during charging, but I have never done that either.
When I feel the AC not as cold and see the high side around 200 or below (ambient starting into the mid 80s), then I top up a couple of ounces to bring it to 220-230 for the season. This ghetto method has always worked for me, so I try not to overthink it.
R134a pressure-temperature chart:
https://www.arkema.com/files/live/si...ture-chart.pdf
Quote:
Originally Posted by E92_William
I’m definitely at a limit of what I know and just now reading up on superheat and sub cooling as I didn’t even know they were a thing. I’ve been watching many videos on it and it seems some cars will have much higher numbers than others.
That -1.5 on the rock auto valve, I figure is in degreees C? I can definitely manage a way to measure these two values but I’d need to know what an ideal one is too.
I don’t think I’ve introduced much regular air into the system, I bled the charge hose before charging 6oz yesterday but I didn’t do the low pressure hose. Maybe that’s enough “air” to cause this? I’d have to keep reading
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