How To Check Thermostat Wires For Short. If you short the R wire to the C wire youve effectively created a very low resistance closed circuit across the secondary of the 24V transformer in the HVAC system. Identifying broken wires on a thermostat is simpl.
If you short the R wire to the C wire youve effectively created a very low resistance closed circuit across the secondary of the 24V transformer in the HVAC system. This picture will be an essential reference to identify wires and correctly install a Nest thermostat. Finding a short in a wire requires you first knowing that the short is there.
Open circuits are usually found by using a voltmeter keeping one meter lead on a common point and walking the other lead through the circuit until voltage is lost.
The meter will indicate an open circuit by displaying OL on its Liquid Crystal Display LCD for a good thermostat that has normally open NO contacts or it will display zero 000 Ohms for a good thermostat. This causes the current in the circuit to be high which may quickly overheat the wires. Touch one of the meter probes to the R terminal to which the red wire is attached and the other probe to the G W or Y terminal and note the reading. In a typical household circuit the circuit would be protected by a circuit breaker or fuse which is designed to open trip to prevent.
