At what pressure does the internal bypass on an r22 compressor open? I was thinking around 400psi. My shop has an old Heil builder model 3 ton unit in it that we took out of a customers house about 10 years ago and installed in the shop and it was already 12-15 years old so needless to say its limping along on its last leg and we've definitely got our "money's" worth out of it. I think I'm going to recover the r22 and change the txv to 410a and fill it up with 410a and see how she screams. Maybe I'll get another 25 years out of the POS... Not going to change the oil, just want to keep my head pressure below 400psi when its hot out and hope the compressor can handles the higher pressure. I'm confident the coil will withstand the higher pressure in just not sure about the compressor, guess I'll find out when it warms up this summer.