ramja
Premium Member
- Model Number
- TWE040E130A1
- Age
- More than 10 years
Our 23 YO split heat pump began intermittently blowing the low voltage air handler fuse about a year ago. Two technicians came out separately after the first event. The first replaced the hard-to-get-to cylindrical fuse with a standard spade fuse holder, inserted a fuse and the system fired right up. To try to figure out the cause he did continuity checks on all the LV wires and replaced the contactor on the outside heat pump. He did say it was out of spec, but probably not causing the fuse to blow. Several days later the spade fuse blew. Different tech came out, put another fuse in, system fired right up again. He rechecked the LV wires' continuity - no shorts. In checking the outside HP he replaced a leaky bulging capacitor. Like the previous tech, he said the capacitor was bad, but probably not causing the fuse to blow. Both techs said the same thing - it's almost impossible to troubleshoot intermittent LV fuse-blowing problems when the system is working. At that point I had already bought a bag of fuses in anticipation of what might be ahead. Actually, there was no blown fuse for several weeks after the second tech came out. However, over the last year 9 fuses have blown out. Some would last a month or two - once two blew in the same day. But every time, regardless of season, the system came back up with a new fuse.
A few days ago, the fuse blew, I replaced it - the second, third and fourth also blew. Even though we were having 100+ degree days I was slightly relieved that FINALLY the system was in a failed state that should be diagnosable. One of the techs that had been out last year came out the next day. He put a fuse in and --- (of course) the system started right up and began cooling down the house. He did continuity checks, inspected the heat pump LV circuit boards and again said hard to troubleshoot a working system - the problem could be any component in the LV system. We had several technical chats during his 2 service calls and the weekend was coming up. He told me if it blew again, I could do some troubleshooting to determine whether the problem was one of the two HP circuit boards, the ECM motor or the fan control board by unplugging each of those components to determine which one's absence led to a stable condition (unblown fuse). And (of course, again) the system went back into the fuse-blowing mode the next day. During my unplugging, replugging and replacing fuse troubleshooting cycles I realized I could turn on the fan and everything was fine. Actually, we ran it several hours that way - just the fan no AC. The system was stable if the thermostat AC set point was above ambient (84F) and no calls were made to engage the AC. However, when the set point was brought down below ambient to start AC and ramp up the fan speed the fuse would pop. I then unplugged both LV circuit boards on the HP and the LV plug going into the motor, so the control board was not communicating with anything except the thermostat, put in another fuse and lowered the set point. After a few seconds the fuse popped.
The question is: Is it safe to conclude that some component on the CNT1866 fan control board has been slowly failing for over a year, has finally died and installing a replacement fan control board will fix the system?
Am I missing anything important?
A few days ago, the fuse blew, I replaced it - the second, third and fourth also blew. Even though we were having 100+ degree days I was slightly relieved that FINALLY the system was in a failed state that should be diagnosable. One of the techs that had been out last year came out the next day. He put a fuse in and --- (of course) the system started right up and began cooling down the house. He did continuity checks, inspected the heat pump LV circuit boards and again said hard to troubleshoot a working system - the problem could be any component in the LV system. We had several technical chats during his 2 service calls and the weekend was coming up. He told me if it blew again, I could do some troubleshooting to determine whether the problem was one of the two HP circuit boards, the ECM motor or the fan control board by unplugging each of those components to determine which one's absence led to a stable condition (unblown fuse). And (of course, again) the system went back into the fuse-blowing mode the next day. During my unplugging, replugging and replacing fuse troubleshooting cycles I realized I could turn on the fan and everything was fine. Actually, we ran it several hours that way - just the fan no AC. The system was stable if the thermostat AC set point was above ambient (84F) and no calls were made to engage the AC. However, when the set point was brought down below ambient to start AC and ramp up the fan speed the fuse would pop. I then unplugged both LV circuit boards on the HP and the LV plug going into the motor, so the control board was not communicating with anything except the thermostat, put in another fuse and lowered the set point. After a few seconds the fuse popped.
The question is: Is it safe to conclude that some component on the CNT1866 fan control board has been slowly failing for over a year, has finally died and installing a replacement fan control board will fix the system?
Am I missing anything important?
