R502 TXV in a R22 system

[AzRob]

What potential problems exist when using a R502 TXV valve in a R22 walk in cooler?
Can correct superheat be acheived at the compressor and evap outlet?

[Dober49]

Hi
You can get away with it but as R502 has a higher working pressure, more problems occur with an external valve, ie flooding back as it will try and achieve higher running pressures. As in reverse if you use a lower running pressure valve, ie R12 it will starve the coil. To be safe always match the TXV to the system. I only ever did it in desperate needs.

[RefTech]

The system will flood as the pressures obtained with 502 in the bulb will be greater than pressures produced by 22 even with no superheat, so the valve will not close sufficiently to produce superheat

[AzRob]

It is an external type with bulb placement in the refrigerant stream.
Given an evap temp range of 20-34 degrees, R502 is about 10 psi higher than R22. Can an adjustable (R502)TXV valve be adjusted to obtain the needed 5-7 degree superheat at the evap? Additionally, the distributor is orficed (to a R22 spec I'm assuming)
There is a hissing sound in the evap, from which I understand indicates a low charge, but sight glass is now clear. I'm trying to get a good picture of the operating principles for this system.

[Dober49]

As before you can play with it to obtain a running system but as temperature conditions and system pressures change the valve won't response correctly, basicly the buld is charge with r502 to match the system pressures. You really need a R22 valve, expandsion valves can effect systems in alot of ways. ie superheats,discharge pressures and suction pressures. If a the vavle is hissing with a full charge(clear liquid line sight glass) then the vavle needs opening. What evap superheats and pressures are getting?

[Dr._Fleck]

I have done it... and i'm not proud of it, it works in an emergency. Dont use a 134a valve on a R404a systen though, it doesn't work at all.

Just treat the system to a shiny new R22 valve.