My 4yr old Amana heat pump quit working - the thermostat display was blank. I replaced the thermostat but still no luck after confirming it was installed correctly. My S/N is 0407477962, Model VNC60C2A,...
Your thermostat can get power from either of two power souces. Primary power would be 24 VAC from a transformer mounted inside your air handler. Second (optional) power may be provided from battery backup, with the batteries mounted inside the thermostat itself.
Since your display went completely blank, then I would venture to guess that it is related to the 24 VAC circuit, sourced from the air handler. You probably do not have battery back up. Use a DVOM (Digital Volt Ohm Meter) to measure the RED wire connected to your thermostat. Make sure to use the VAC setting on the DVOM.
The "hot" side is the red wire, and will be connected to the "R" terminal in your thermostat. The Common side will be connected to most likely a blue, a black, or a brown wire. The Common terminal will be labeled "C" (but perhaps B) on your thermostat.
Since the thermostat is just plain dead you should next locate and check the fuse or breaker for the air handler control circuitry. There may be multiple different breakers/fuses for your heat pump's outdoor circuitry, its indoor controls, and its indoor resistive heat strips. Also, the circuit could be either 120 VAC or 240 VAC. Has one of them tripped or blown a fuse?
If you have breakers, then flip all of your breakers off and then back on. Stay near the breaker box and wait for a minute, listening/looking to see if any breaker has tripped or if a fuse has blown. Otherwise, if the circuit is fused, then examine or test the fuse. Again, use your DVOM, this time in the Ohms setting. Zero Ohms indicate the fuse is good. A very high Ohms reading is a blown fuse (infinite resistance) In this case, verify that the blown fuse is the CORRECT value. Maybe it isn't. Replace it with the correct amperage fuse. Again, wait a few moments and see if it the new fuse blows.
If either the new fuse immediately blows, or if the flipped breaker immediately trips, then STOP and call a professional. You have a high-power wiring problem. Call around, and find an expert. It could be that a mouse chewed thru some insullation. You don't know, but don't be sold on replacing an expensive component without verifiable proof of the source of the problem.
Otherwise, go back and check your 24 VAC "R" Red terminal at the thermostat. If it reads 24VAC hot now, then you have solved the problem, at least temporarily. You now need to know why the breaker tripped or the fuse blew.
If the circuit is on a breaker, then just replace it. They really do go bad after a while. Pop the old breaker out and bring it with you to the hardware store. Replace it with the correct brand, amperage, and configuration.
If the circuit was on a fuse, then (a) was it really the correct amperage rating? or (b) is there a chance that you had a hit from the power company or a nearby lightening strike? (probably not, or some of your computer/stereo/other stuff would have been knocked out too.)
Otherwise, you know the source circuits are good, and you know you don't have 24VAC at the "R" terminal of your thermostat. There are now more possibile causes.... to be continued. Marty
Dec 09, 2009 |
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