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

[richtj99]

Hi,

I have an older Honeywell trol-a-temp thermostat which I managed to break. I am posting images of my items, but can I just replace it with a digital thermostat? If not, can I buy something off of ebay or somewhere else that might work?

Mastertrol Mark V, 2 zones.

If i put two of the wires together, I can get it to turn the heat on, the other two wires will turn the air conditioning on. There are a total of 3 wires for this.

The way the setup works, is I have the master control of heat, fan, or A/C in an office, the thermostats are all set on their own, when i turn on the master control to one of the three selections, the heat/a/c goes on & the thermostat will stop calling when ti gets to the temperature.

Is there some way for me to make this work with a three wire thermostat?

Thanks,
Rich

[small change]

This is not a diy site. I hesitate as to what advice I can give you

For Example......I have no idea what voltages you are working with here.

Maybe call a pro in this instance...Check our map for one in your area.

Did you break the Vessel that held the mercury?

[richtj99]

Hi,

Sorry I didnt realize this was a DIY question. What happened is during some painting, the old thermostat was removed from the wall & then somehow thrown out. I have the wires sticking out. I called my HVAC guy who said they dont make those thermostats & I should buy a new $ system. I really only want to replace the thermostat until the system does finally die (it is from 1983). I know its on borrowed time, but its a new to me house.

I am guessing the guy was more interested in selling me a huge system vs helping me find a replacement thermostat.

I am not looking for DIY, just more a direction to look to get a replacement thermostat.

EDIT: the guy did say something regarding it had to be a mercury thermostat which sounded wierd to me.

Thanks,
Rich

[mark beiser]

Since you have a separate changeover control in the system, you can use pretty much any mechanical, or battery powered digital, thermostat in place of either of the zone thermostats.
Any competent tech should be able to figure it out, but some guys don't even try when they see numbered terminals instead of R, Y, W, etc..

There is also a way you can wire and configure some heat pump thermostats to zone 1 that would allow you to eliminate that ugly old changeover control, but you need at least 6 control wires to the zone 1 thermostat location, and at least a basic understanding of how that system operates.

[beenthere]

White Rodgers has digital stats that work fine with those systems. I'm sur others do too. Some techs just go for the upsale.

[mark beiser]

White Rodgers has digital stats that work fine with those systems.

Yeap!
Pretty much any battery powered digital will work, but White-Rogers is the only brand I know for sure has thermostats that can be used as the Zone 1 thermostat when the system doesn't have a changeover control, or if you want to eliminate an existing one.
With a White-Rodgers single stage heat pump thermostat, that has separate B and O terminals that get powered even when the stat is configured for gas heat, installed as the "zone 1" thermostat, you can eliminate the changeover control.

[vstech]

and that thermostat is NOT mercury. it's an old magnet style. they still sell them at lowes...

[54regcab]

I've seen those stats used in mobile homes where the heat/cool switch is on the furnace.
It's a standard "heat only" thermostat.

[mark beiser]

I've seen those stats used in mobile homes where the heat/cool switch is on the furnace.
It's a standard "heat only" thermostat.

It isn't one of those 2 wire mobile home thermostats, it is a 3 wire(R, W, Y) heat/cool thermostat.

[54regcab]

It isn't one of those 2 wire mobile home thermostats, it is a 3 wire(R, W, Y) heat/cool thermostat.

I didn't see the 3rd wire in the photo, but I see where he described it. Looks like one of the WR stats may be the solution...

[Krzyd]

Hi,

Sorry I didnt realize this was a DIY question. What happened is during some painting, the old thermostat was removed from the wall & then somehow thrown out. I have the wires sticking out. I called my HVAC guy who said they dont make those thermostats & I should buy a new $ system. I really only want to replace the thermostat until the system does finally die (it is from 1983). I know its on borrowed time, but its a new to me house.

I am guessing the guy was more interested in selling me a huge system vs helping me find a replacement thermostat.

I am not looking for DIY, just more a direction to look to get a replacement thermostat.

EDIT: the guy did say something regarding it had to be a mercury thermostat which sounded wierd to me.

Thanks,
Rich

Just looking at the T-stat pictures I thought you needed a new system too, if you have a good relationship with your HVAC guy and you trust him, why wouldn't you trust that your 30 year old system needs replacing? If you don't trust him then call another company, I'll bet they tell you the same thing.

[richtj99]

I have a brand new relationship with the HVAC guy. Really I would rather find a thermostat that works, give it a year or two & get another system when I am ready.

I was looking on google shopping: Links to direct purchase sites are not permitted.

Would this one should work? I also was looking for the mobile home style ones but I would appreciate any recommendation. Again I am not looking for help installing it, I just want to know which thermostat will work.

On one hand, I have the HVAC guy saying no thermostat in the world will work but one from 1983 vs you guys saying that pretty much any three wire one should work. I am expecting that you guys are correct.

THanks,
Rich

[BaldLoonie]

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!

[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.