I am replacing an old dial Trol-a-temp thermostat. It has three wires; red, white and yellow. The thermostat only regulates the temperature as the main switch for cool and heat etc. is in another separate location. I have gas and two zones. What can I use to replace this??

Back in 1999 Honeywell bought Trol-A Temp from Trolex Corporation. Finding a big selection of thermostats for the old style system is a problem so read below and call Honeywell for an answer.

For all questions concerning this thermostat, please read and follow the instructions. If additional
Assistance is needed, call Honeywell Customer Assistance toll-free at 1-800-468-1502, Monday
Here is the reason you need to contact Honeywell.

T8621D7063 Trol-A-Temp® by Honeywell logo; system switch:
HEAT-OFF-COOL; O and B terminals.
None See Trol-A-Temp® representative
for replacement.
T8621D7071 Trol-A-Temp® by Honeywell logo; no system or
Fan switching.
None See Trol-A-Temp® representative
for replacement

It says there are no replacements available but I believe there is. Call Honeywell.

BTW

You need a single stage heat pump thermostat with separate O and B terminals.

I realize that you do not have a heat pump, but your zone system uses the O and B heatpump terminals to determine heat or cool mode.

Honeywell search results.


http://customer.honeywell.com/Honeywell/CatalogNavigator.aspx?Definition=Search&Catalog=&C hannelID=%7B96CDA7E5-4A39-47AC-98EA-E78614E28BD2%7D&ReturnUrl=http://customer.honeywell.com/Honeywell/UI/Templates/CMSTemplates/Base4Column.aspx?NRMODE=Published%26NRNODEGUID=%7B 40A4279D-9BFB-4F9E-AC70-76670E0646B2%7D%26NRORIGINALURL=/Business/Cultures/en-US/Default.htm%26NRCACHEHINT=Guest