How to Trouble shoot Low Voltage Controls on AC-Heat

What I have always been told is if your 24 volt side burns out check the high volt side if the hi volt side burns out check the low volt side.

A quick way if the primary side is burning out due to a problem with the low volt side:
1* Mark all the thermostat wires at the indoor unit.
2* Disconnect them at the indoor unit.
3 Check main line voltage before proceeding (A on electric furnaces, 208 volt is not considered 220V and 240v Is not considered 208V. In these circumstances the voltage may have changed with the power company replacing a transformer and now you need to change the main power input lines at your control transformer for the correct operating voltage). If OK then proceed:

4 If you have an amp meter attach it to one of the lines going to the transformer.
5 Apply main power and listen for hum, note if smell starts again and if so problem has to be in board or main incoming voltage too high or too low. Amp draw should be less than 3 amps.
6 If your to this point and still haven't found any trouble in the above as of yet, Connect the wire marked "C" together. Then just touch the thermostat wires one at a time to the places where they go on the indoor unit and watch the amp meter. If you don't see the meter jump the circuit is probably OK but leave them disconnected until you touch all of them to the correct place or wire. Here is a possible problem I have seen a thermostat wiring problem if the wires are stripped too far and a "whisker" of the wire sticks out and allows one of the other wires to cross short out. In this case just cut off the excess wire or bend it over out of the way and continue with the test. You can always cut it off later after the tests. If you see the meter jump up and stay up and /or blows the fuse the wire that you used and it blew is where to concentrate.

(* you may need to reattach the wires at the indoor section then disconnect them at the Thermostat and then at the out door unit if you have not discover the cause at this point or after finding the wire(s) that cause the Spike on the AMP meter. Just take your amp meter with you and reconnect the "R" wire first and check it first. after that if nothing shows at each place connect the "R" back and proceed with touching each other wire individually while amp reading the "R" wire).

7 No wiring problem found means that you could have a relay or contactor not pulling in properly.
and this will cause the amp draw to go way over the transformers power out put or VA rating.
8 Inspect the thermostat wiring for the "whisker" I mentioned above.
9 If you have done this to the end of the thermostat wires and your main incoming voltage is correctly wired in on the transformer and your relays and contactors are pulling in evenly and not delaying excessively your problem should be fixed.

If this helps you please rate me as high as you can and thank you for using fix ya.