OK... so in trying to install a thermostat (and testing to see if the old thermostat was bad) I inadvertently jumped the R and C... (I actually jumped the R and G terminals but the G terminal was connected to the C terminal back at the HVAC). So I shorted it out, no? How bad might the damage be?
If you short the
Ohm's law says that current (I) in a system, is equal to voltage (V) divided by resistance (R). If we assume it's a 24V transformer, and that there's 50' of 18 AWG wire between the transformer and the thermostat. So voltage is 24 volts. We'll say resistance is about 0.6 Ohms; since in this example we have 100' of total wire in the circuit (50'
V = 24
Since 18 AWG wire is only rated to carry 14 amperes @90°C, the 40 amperes running through the wire could be enough to damage it.
Wire resistance and ampacity values from WikiPedia
The first thing you should check, is to make sure the circuit breaker for the HVAC system is not tripped.
If the breaker is not tripped, it's possible that the coil wires in the transformer or the thermostat wires are damaged. You'll want to start by doing a continuity test on the
You'll also want to do a continuity test on the secondary of the transformer, to insure it's not damaged. To do this, you'll have to completely disconnect the transformer from the wiring, which means you'll also have to turn off the circuit breaker (and make sure power is off with a non-contact voltage tester).