Superheat Correction facter for R12-TXV - R134a?

[The MG Pony]

Ok I have a Singer M:207C TXV for R-12 (Same as the american Control company TXV) it comes preset to 9F (-12C) superheat.

It is a 6,000BTU/hr unit (1.76 KW/hr) liquid cross charged head internaly equilized


I'm thinking I need to set the super heat higher for it to work correctly with R-134a correct?

Thanks guys for any Help.

Head pressure during pull down is 150PSI

[US Iceman]

it comes preset to ... (-12C) superheat. ...
I'm thinking I need to set the super heat higher for it to work correctly

You must have made some kind of error in your calculations.

If you are running a negative superheat, that is a unique kind of refrigeration system you are working on.

If the evaporator has any appreciable pressure drop, the internally equalized valve may not remain stable no matter where it is set at.

[Josip]

Ok I have a Singer M:207C TXV for R-12 (Same as the american Control company TXV) it comes preset to 9F (-12C) superheat.

It is a 6,000BTU/hr unit (1.76 KW/hr) liquid cross charged head internaly equilized


I'm thinking I need to set the super heat higher for it to work correctly with R-134a correct?

Thanks guys for any Help.

Head pressure during pull down is 150PSI

Hi, The MG Pony

I think in this case this 9F means 5K or 5C but only like a difference, because the superheat we always write in K and K is always positive number, there is not negative temp shown in K scale at all.

So if you run your sistem at 9F(-12,778C) your superheat will be 18F(-7,778C) (difference of 9F or 5K or 5C)

For *****s it is Ok to have min of 5K, with ammonia you can go to 0K.

Best regards, Josip

[The MG Pony]

This is what I read off the TXVs manual it is presset to 9degrees fehren?

I guess there is no sort of correction facter eh? just a good thermometer and a set of guages and some time tuning it all?

But if it is going as a differance then is there some basic way to set it correctly to work with R-134a? IE Increasing super heat or reducing it slightly to match the R-12 curve.