Hi. I have a Trane gas heat/ AC unit thats about 18 years old. Untill 2 weeks ago it was working perfectly. Sudenly, it stopped working and nothing would come on. I checked the control unit and there was no power. My trane has a white-Rodgers 50A50-403 control unit. I bought a new 50A55-843 which is the replacement and still nothing worked. After checking everything, I noticed that the transformer was dead and ordered and replaced said transformer. I installed the old control unit back and when I switched on the power, the unit's light started flashing normally. I also heard a humm from the transformer. I went upstairs and turned the AC T-stat on. The blower started running but the compresor/condenser unit did not kick in. I went to the control unit and noticed that the red light was flashing very rapidly and then it went out. I verified all conections and even checked the breaker and all was okay. When I touched the new transformer and it was hot. The diagnostic light does not come on and not even the blower will work. The old control unit does not have a fuse to protect the transformer. I'm at a loss, what can I test next? One last thing, last year I replaced the contactor for the compresor/condenser unit because it would not stop running. Thanks for your help.