Started having an issue with this chiller where the EXV was freezing up on circuit 'A', which is a tandem circuit, one of these 06Es was just replaced. Well, the EXV was freezing up then locking out on code '68', low superheat.(which from what I was told was doing that even before this compressor locked up). Since I knew I didn't have low superheat (pressures were 160/5), I checked all the thermistors, they all ohmed out properly with the corresponding temperatures that they were at, checking some tech docs on it, the only other things that it says could cause this code was a stuck EXV (stuck open) or misplaced thermistors. Verified thermistor location, ohmed them all out again, all checks out good. So, the EXV appears to be the culprit, it gets changed out. Same. Damn. Problem. There were new thermistors on-site, so I pulled both off of the board that served circuit 'A' on the refrigeration side, the one on the compressor, and the one on the chiller barrel, I hooked up the two new sensors but left them sensing outside temp, around 85deg (I did this for now because replacing the sensors is extensive since they don't have immersion wells, and they were ohming out fine). It still would not open the EXV. Now....circuit 'B'. this one only having one 06E, the compressor runs fine, good charge and on a semi warm day can pull the chilled water down by itself, however when we come back after leaving it running (while waiting for parts on circuit A) that circuit (B) is also down, locked out on a code 55. Now, at this point I want to lean towards it being the board, but I just don't know. A new board is on its way in the A.M. but I want to hear from you guys as other possible issues, carrier tech support was zero help, and told me they did not support, or could help with a chiller that old, please help. I want do well for this customer, they are a church and are in desperate need of getting this fixed, Thanks in advance.