Working on an r22 pos eco temp in cooling mode high side 198 low side 62 its about 75 inside. Switch it to heat mode and the common port drops to 6 psi cap tubes freeze up. 3/4 side goes to 165 and the 3/8 goes to 21. freezes up from service valve to the tips of the cap tubes. Took it apart flushed the system, checked the piston (No TXV) blew nitrogen through it as well as hit the service port with rx-11, change the biflow filter, vac system back down re charged it in cool mode and again it is back to the same crap. Note: I have thought of everything on this inside coil is clean the fan motors run good no problem with the line set. The only thing that I can now think of is that I should change the the txv in the ahu thinking that check valve is clogged. However, that is why I am on here right now trying to get some feedback........ This is the crap I love, dec 25th service call rom hell.