Need help with funky thermostat wiring

Dealing with 240v here...one stat, two heating panels.

My thermostat was worn out and I recently purchased a new one to replace it. It was not turning on and off at the right temp. There are four wires in the electrical box, so I purchased a four wire Honeywell thermostat.

When I took off the old stat I discovered some funky wiring. The two white wires were taped together, and the two black wires (both hot) were going into the old thermostat which was not marked at all, it's an old one from the 60s. There is a black and white wire connected to the breaker.

When hooking up the new stat, it works three different ways and I need to know which one is correct. First, it works when the two blacks are connected to L1 and T1, and two whites are connected to L1 and T2.

It also works if I leave the two whites taped together, jump T1 and T2 together, and hook the two blacks to L1 and L2.

The final way it works is if I again leave the two whites taped together, jump L2 and T2 together, and hook the two blacks to L1 and T1.

This was a funky setup when I first pulled off the old stat and can't find any diagrams that match it which is why I'm experimenting. I'm concerned that I'm going to do something that bumps it down to 120v. I was also considering hooking blacks to L1 and L2 and jumping T1 and T2 over to the taped together whites.

Someone also suggested over on another forum to also splice the blacks together and run a third wire from each splice and just treat it as if I had one black and one white wire.

 

The supply wires go to the L1 and L2 terminals. The heater wires go to the T1 and T2 terminals. The white wires should be "re-identified" with permanent marker or colored tape to any color other than white, grey or green to denote this is a 240 volt circuit. Use the same color for both white wires. Convention has the black wire on L1 but it really doesn't matter.

 

The problem is that when I disconnect all of the wires and they are standing alone, only the black wires are hot. I would also think that since there is a black and white connected to the breaker, that the black and white at the thermostat box should both be hot, but they are not. Only the black two are hot.

 

How are you determining which wires are hot?

 

A tester with two leads and a light bulb.

 

A 120v light bulb ? What happens when you test 240v ?
Or is that a little neon bulb type tester ?

As I told you in your other thread on the same subject.... a four terminal stat has two distinct switches in it. Post the model number of the new control,