Originally Posted by
denman
Is 120 supposed to come in from each side? Or is 240 supposed to come in on one wire?
OK so I will try to give you some info on how most units are wired.
First how 240 works just in case you do not know this.
The unit has L1, L2 and Neutral.
L1 to Neutral is 120 volts.
L2 to Neutral is 120 volts but it is 180 degrees out of phase with L1.
So when L1 is at positive 120, L2 is at negative 120.
Therefore L1 to L2 is 240 volts.
Now the wiring on most units.
The L2 side goes to the centrifugal switch. It closes when the motor gets close to operating speed. Then it goes to one side of the heater.
L1 goes through a set of timer contacts, then a thermal cut off (fuse), then the operating thermostat then a high limit thermostat, then the other side of the heater.
The heater is not grounded or attached to Neutral so you get 240 volts across it if the timer contacts are closed, the thermal cutoff (fuse) is good,the operating thermostat's contacts are closed , the hi-limit thermostat contacts are closed and the centrifugal switch is closed.
It can be confusing to troubleshoot this using ground or Neutral because you cannot tell which side of the line you are measuring.
With the unit off (motor not running you get 120 at the heater you can assume that the thermostat/timer side's wiring/parts are good.
You will also see this 120 at the other side of the heater.
The trouble then is probably that the centrifugal switch is not closing.
if you only see 120 at the heater when the motor is running then odds are the problem is on the thermostat side.
I hope this helps and that I did not make it confusing.