Honeywell
T8090A/Q682B
Heating, Cooling, and Heating/Cooling
Thermostat, Wallplate and Subbase—
Installation Instructions
Preparation
Check thermostat and subbase (if used) suitability for
the heating, cooling, or heating/cooling system. Refer to
Table 1.
Assemble tools required: flat-bladed screwdriver, hand
or power drill with 3/16 in. drill bit, wire cutter/stripper or
sharp knife, bubble level or plumb bob and line.
Assure power is off to the heating, cooling, or heating/
cooling system at the main fuse panel. Most buildings have
a separate switch box or circuit breaker for disconnecting
power to the heating and cooling (if applicable) equipment.
This thermostat is compatible with all heating, cooling,
or heating/cooling systems when thermostat is powered by
batteries. If thermostat is not powered by batteries, refer to
Table 1 for thermostat and system compatibility informa
tion.
TABLE 1—SYSTEM COMPATIBILITY FOR NON-BATTERY POWERED THERMOSTATS.
Type of Heating System
to be Controlled Conditions/Compatibility
Electric (Line Voltage)—typical
baseboard and radiant
• The R8239D1015 Isolating Relay or R841 Silent Switching Center
must be installed in the thermostat control circuit.a
Gas—Direct Spark Ignition (DSI),
Intermittent Pilot (IP), and Standing Pilot
(SP)
• Compatible. If not using battery backup, assure that 24 V control
transformer common is accessible for connection to thermostat
cable conductor and power to the transformer is not regularly
interrupted by high temperature or limit operation.
Hot Water Zone • Honeywell 2-wire valves are compatible.
• Some non-Honeywell 2-wire valves require an R8239D1015
Isolating Relay in the thermostat control circuit.a
• Some 3-wire valves require an R8239A1052 Isolating Relay in the
thermostat control circuit.a, b
Oil • If not using battery backup, assure that the 24V control
transformer common is accessible for connection to thermostat
cable conductor and power to the transformer is not regularly
interrupted by high temperature, purge cycle, or limit operation.
Vent Damper • Honeywell damper motors are compatible.
• Some non-Honeywell damper motors require an R8239D1015
Isolating Relay in the thermostat control circuit. a Check control
amperage requirement.
Warm Air Zone
• Most are compatible.
a If thermostat is not compatible with the system being controlled, the system will not operate. No hazard exists. The thermostat
will not be damaged unless it is used to directly control a line voltage system. For proper system operation, a Honeywell R841
or R8239D1015 Isolating Relay must be added to the thermostat control circuit.
b Consult manufacturer for installation requirements.
D. F. • Rev. 11-94 • ©Honeywell Inc. 1994 • V2 Form Number 69-0627B— 1
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