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Re: analog thermo.stat control kit
Have you tried removing the RH wire connected to the thermostat and try it ? This might rule out furnace as short in system. If it does the same, put RH- (heat) back on and try removing RC-(cool) , if it doesn't pop the fuse, you may have isolated the problem.?
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The "R" terminal on the back of the stat should be 24 volt supply to the stat. For a heat pump, when the stat calls for heat, the "W" terminal goes hot (24 V) and should actuate the reversing valve and start the outside unit for heat. when the stat calls for cooling, The "Y" terminal goes hot and starts the outside unit without the reversing valve. The heat strip is used to temper the air while the outside coil is defrosting when in heating. You need an OHM meter to test for a short in the heat strip. A lot of installers are wiring it to heat all the time when in the heating mode if the heat output is too low on really cold days. Try jumping "R" to "Y" and the outside unit should start. Disconnect the heat strip from power while testing. This is really brief, its a big subject. Good luck.
disconnect the thernostat wires from the control board. Put a jumper wire between R & G put door back on and turn on power. Blower motor
should run, if it blows the fuse then you have a direct short between R &
G at the board. Do this with R and W(heat) and R & Y(cool).
By disconnecting the thermostat wires and reinserting them make sure that they do not touch when inserted into each terminal. If it still blows
that little 3amp fuse when jumpering between each sequence as mentioned above, then I think your board is bad. When Jumpering out the Y terminal you will have to have the AC wires still hooked up. If it
blows the fuse in that sequence. Disconnect the wires out at the condensor.
Disconnect the yellow wire from the thermostat and tape off the end. Turn the power back on. If the fuse blows, it is not in your wire nor the compressor contactor. If the fuse does not blow, turn off the power, reconnect the wire, and replace the fuse. Then, disconnect the wire from the compressor contactor and tape it off. Turn the power back on. If the fuse blows, it will eliminate the compressor contactor coil and will likely be a "short" in the wire itself. The yellow wire goes from your T-stat to your air handler and from your air handler, it goes to the oudoor unit's compressor contactor.
The three amp fuse is installed in the board to protect from shorts or overloads created by disconnecting or reconnecting components when DC power is still connected to the system. If the fuse is blowing, then you more than likely have a short in the 12VDC system between the control unit and the thermostat.
1. Pull the cover off of thermostat and remove the +12 (or +7.5 depending on the model) wire. Access the other end of the wire in the AC compartment. Using an ohmmeter, touch the end of the wire at the AC with one lead and touch the control box with the other (or any ground source). If you get a reading other than OL or Infinity, then that wire is shorted out in the wall somewhere. If not, repeat the steps for the rest of wires except the ground of course. If all of these wires appear to be fine, you may need to take it in for some more extensive troubleshooting.
The 3 amp is 12 Volt protection for the control board. If that fuse is blowing instantly, then you have a short in the 12 Volt system somewhere. More than likely it is somewhere between the Thermostat and the control unit. Check to see if you have 12V at the thermostat. If so, then disconnect the red wire from the thermostat and the red wire at the control unit. At the control unit side, use an Ohmmeter to see if you have continuity with ground. If so, that wire is the culprit. If not, reconnect the red wire and continue to the next wire. Do this until you find the wire that is shorted to ground. Of course, the ground wire will not be checked.
If you are running the AC on an extension cord it can cause such voltage drop that a fuse or breaker can blow, in extreme conditions it can damage electrical connections. Always use extension cords that are as short as possible and replace the cord ends (especially the female end) whenever they lose clamping force. A heavy duty cord end takes much more effort to plug in the male end and to plug things into the female end. Over the counter extension cords for your purpose should be no less than 12/3 with heavy duty (20 amp) ends and no more than 50' long, if you must go farther you should use a 10/3 cord.
Check your furnace for power. will be 4 wires. power ground and 2 thermostat wires. Check for power at the time delay relay, if you have power there check for power going in the fan motor, if power in motor wire, motor is bad. If no power in motor wire and power going to circuit board take the 2 thermostat wire apart and wrap the 2 together comimg from the thermostat. Fan will stat in about 30 seconds. If it does you need a control kit in the ac. But sounds to me like you have a furnace problem.
Had one doing similar recently, and after a thunder & lightning storm. Nothing worked, but kept blowing 2 amp fuse in thermostat, when anything tried, heat or cool. Pulled plastic control box down from inside upper unit (AC) made sure breaker was off, took of plastic cover and smelled inside, and could smell burnt plastic smell. Replaced, control box, that got fan only working. Tried another thermostat , everything worked as it should. Turns out the lightning, or power surge, or whatever, shorted out the thermostat, and control box at same time.