Quote Originally Posted by Nereferman View Post
Yes txv is sized correctly. Before we added rawal valve set up it was liquid slugging. Once the hot gas bypass was installed and set up that went away. We did run really high discharge superheat with this set up at first because it was hot gassing so much. I ended up lowering head pressure with my head pressure control valve and playing with the charge. We had 90 lbs of 407c at first and currently as it sits we are at 74 lbs with half way decent superheats. The rawal set up is by passing at its max capacity. When I pulled the valve plate the nickel coating on it had been washed off and it was down to the copper plating. At first I though it was due to velocity being high in the suction line from the hot gas, but now my thoughts are that it is due to just hot gassing so much it’s cooking up the compressor. I am concerned that when we add the low temp coil to this circuit that the compression ratio is going to be to high and we will be running those high discharge superheats. I looked into going 407a but I struggle to understand what that gives me. On pt chart they are slinky 2psi apart at -20 and 200 deg. I have not found a glide chart yet for both to compare glides yet. But is the 407 family of gas my best option. Should I go to 404a at this point?
Sorry I meant, is the TXV head/power element for the correct refrigerant?

I've only ever come across 407C and 407A on medium and high temp equipment. R404a may be the better option.

For me, I think I would be looking at what capacity I really need. Sort of sounds like even if you put an EPR on and run the -20 and +35 on the same comp, you may still be recirculating a lot of hot gas.
If comp capacity still works out to be way too high and you dont have the option of changing the comp size, maybe an alternative capacity control method should be looked at.

Keep an eye on your thread, others may post better advise.