______________________________________________________________________ Thanks for your help on my Trane XL12 heat pump. It was low on freon and the low pressure shrader valve was stuck open. Here are the LED codes for a 2TWR20xxA1000AA heat pump (the xx can be any number). It goes by the speed of the flash. 1 Flash per second = Normal 2 = Fault A (low delta T) – Inop Compressor, loss of charge, open amb. sensor, shorted coil sensor. 3 = Fault B (20 defrosts terminated on timer) Fault C (high delta T) – SOV stuck in heating, shorted amb. sensor, open coil sensor, closed TXV, OD fan motor failure, OD fan on in defrost, undercharged unit. 4 = Faults A & C or A & B. Hope this helps someone. This is allot like when Ford would give out their diag codes to only authorised dealers !!! Sorry he just left. Replies: xenos Webmaster “Re(1):LED Codes for Trane XL12″ , posted Fri 26 Dec 13:15 ______________________________________________________________________ Thanks for posting the codes. They will come in handy. Xenos. The best way to escape a problem is to solve it. justleft “Re(2):LED Codes for Trane XL12″ , posted Fri 26 Dec 13:23 ______________________________________________________________________ What is “delta T” ? Sorry he just left. xenos Webmaster “Re(3):LED Codes for Trane XL12″ , posted Fri 26 Dec 13:33 ______________________________________________________________________ Temperature Difference. Xenos. The best way to escape a problem is to solve it.