Broke older style mercury thermostat - can I get a replacement? Trol-a-temp

[beenthere]

With that ancient panel, can you have your switching on a thermostat? Seems to me no but we haven't had a customer with one of them in many a year. They've all modernized!

A master stat can be installed.

That is a relic of a zone panel.

[BURL-REF]

I just went through this with my customer. Oil burner tech offered 3 new t87 stats with new oil furnace. What a mess he had. Those stats are not available anywhere I looked. They are not your conventional t-stat , even though its 3 wires. A new zone system is in order for you unless you can find the stat that was misplaced or thrown out.

[BURL-REF]

Just so you dont waste time searching the web for a new one, they mandated all mercury stats taken off the shelves , and not to be sold. Some company picks them up as they are hazardous waste.

[BaldLoonie]

This isn't a Honeywell, it's a Robertshaw. It is not mercury, it is snap action.



Still think I'd investigate a modern panel that can accomodate future needs like dual fuel and staging. At minimum, they'd have capacity control. Then you could use any thermostat you wanted.

[mark beiser]

They are not your conventional t-stat , even though its 3 wires. A new zone system is in order for you unless you can find the stat that was misplaced or thrown out.

A conventional thermostat will still work, he will just need to make sure the thermostat is switched to the same mode as his changeover control.
The current thermostat has a 24v input, an output for heating, and an output for cooling.
It isn't very difficult to figure out how to make a conventional thermostat work with that.

The only residential zoning system you might be straight up screwed if you broke a thermostat for would be the master thermostat for an old Lennox 2 Speed zoning system.

[kangaroogod]

Mark, I believe the stat needs a reverse call in heating on y to power m6 and close the damper. I could be mistaken but I am pretty sure.

[BURL-REF]

Mark. these thermostats are called type 2, there is no deadband on them, they either make r&w or r&y. There is no in between.

[mark beiser]

Mark, I believe the stat needs a reverse call in heating on y to power m6 and close the damper. I could be mistaken but I am pretty sure.

Mark. these thermostats are called type 2, there is no deadband on them, they either make r&w or r&y. There is no in between.

The Trol-a-Temp brand has changed hands a number of times, and there were a number of changes to them in the 80's and 90's, so I could well be very wrong.

Looking more closely at the picture of how the the damper motors are wired to the panel, it looks like the old 5 wire actuators, so I'm thinking that you guys are correct and that I am wrong.
A regular thermostat would work for the calls for heating and cooling, but the dampers would not operate correctly.

The oldest documentation I can find is for the version available in 1991 that is able to do 2h/2c heat pumps, and works with a variety of damper motors, and definitely will work with regular thermostats. I've worked on a bunch of the late 80's/early 90's Trol-a-temp panels, but I guess I haven't done anything with the older ones besides tear them out during complete system changeouts.

If the reverse call to close the damper is needed, it could still be done, but it would require a minor modification to a mechanical thermostat, or couple of relays.

Some installation instructions for that specific model would be nice to have...

[richtj99]

So i took a few more photos to help sort this out. I am hoping to just plug the three wires into a battery thermostat. The thermostat should only call for heat or cold, the master switch (gold one) should do the actual on, off, heat, ac. So if the system is turned off & the thermostat is set for A/C, it should try to call but nothing should happen until I turn the master switch on. At least thats how I envision it working in the current strange setup.

I plan to replace the unit in 2 or so years, so if I could get some sort of usage from now until then it should be fine. Half the summer, i had two wires connected to force the system to call for AC, when it got to the right temp, I would unhook the wires. Then we found hte old thermostat - at least for one part of the office.

[kangaroogod]

Your logic is not accurate. It requires a call for heat or a no call for heat in heating and a call for cooling and a no call for cooling in the cooling mode. For example if you call for heat and then remove the thermostat from the wall the damper will remain open. Honeywell makes a simple stat for that system but the model number escapes me. Their are very very few stats that work with that setup. Trol a temp systems ruin equipment as they have no provisions for freeze protection nor overlimit protection.

[richtj99]

So is there any type of thermostat that would work for my situation?