Have you removed the load on the secondary of the transformer? With the power switched "OFF", have you measured the resistance between the leads that would connect to the secondary of the transformer? Does the thermostat work?

Can you post a full schematic of the circuit?

IMPO

SR

I have removed the load from the secondary and I get no voltage out of the transformer. I have not ohmed out the transformer but will do so when I get there today.

( the second transformer has the same problem as the first and the original transformer is working well in the other unit).

No secondary to the transformer.

FYI: The AH has its' own DPST breaker that serves the transformer directly..Both legs are 120V from the DPST to each of the primary legs of the transformer.

There is a heater in this unit, but I do not know which.

Sounds like a flaky connector.

If it is a 120/24V transformer and you measure 120V on both wires on the primary, you most likely have an open neutral somewhere in the house circuit. What did you use to measure your 120V?

The transfromer line side has three posts 240V- 208V-COM I have 120V out of each side of the DPST and 120V to each connector serving the transformer. Also, I have numerous units that are identical to the problematic unit ( same DPST, transformer, all in the same location and there is a factory window in the cover of the AH to view the DPST...Its' suppost to be there.) When the T-stat is satisfied, I have 24V from the transformer and to the stat on all of the functional units. No 24V from the problem unit. I swapped out stats just for the sake of doing it..No change. FYI: I am using my Fluke meter

Schematic is low res & incomplete. Only shows wiring until, "See Installation Instructions For Proper Low Voltage Field Wiring Connections". That part of the schematic would be helpful - BUT - I actually see that you're probably smart enough to figure this out on your own (with your Fluke).

Post back the rest of the schematic - But I think you will solve this first before anyone else.

IMPO

SR

1. This is a 240v furnace. It is supplied by 240v, not 120/140v. There is no neutral. So if you measure one leg to the case (which is grounded), you will see 120v. If you look at the other leg to ground, you will also see 120v. There should be 240v across both legs.

2. did you notice there is a fuse on the 12v side?

Re: weedmeister

"2. did you notice there is a fuse on the 12v side?"

True enough - I missed that on the low-res diagram. Great Point, the OP probably spotted that.

You're right about the 'Neutral' as well.

IMPO

SR