Sorry to take so long to reply. I had to order parts, wait for them to arrive, install the new parts, and check everything out. Also, I am SLOW (but methodical)!
I checked everything that you suggested, and all checked out fine. That left the ECC Control Unit itself. I found a unit on EBay with the same serial number as my non-working unit at a great price. When it arrived, I installed it and found that everything was functioning. However, the AC compressor was not coming on, so I had no cool air. I discovered through the diagnostic feature in the PCM area (the HVAC area had no error codes), that the compressor clutch relay was bad and the compressor clutch circuit was also bad. (The diagnostic feature of the ECC Control Unit is GREAT!). Checked the relay (which was good prior to installing the new unit) and it was bad. Replaced the relay, but the compressor did not come on. The relay error code was gone, but the compressor clutch circuit error was still showing. So, I started over by checking the fuse in the inside fuse box (which had tested fine earlier), and found that the fuse was bad. Replaced the fuse and everything works great! All error codes are gone, too! I have run the AC for quite a while to make sure that the relay and fuse remained good. I must have done something during the checking out process and/or the install process to make those items go bad. But all is working great now!
Thank you for your help. I learned so much about a subject that had been completely foreign to me.
Tuesday, April 30th, 2013 AT 9:24 AM