MORTEXPRODUCTSINC.501TERMINALRDFORTWORTH,TEXAS76106 Page28
Separate Heating and Cooling System; Same Thermostat
If the furnace and the cooling unit have separate transformers be
sure to use a thermostat with isolated heating and cooling
contacts “RC” and “RH” to prevent interconnection of Class II
24 Volt Systems. Cycle furnace and the air conditioner
separately to make sure it will operate correctly.
Most new thermostats have separate heating and cooling
contacts for use with homes that have an air handler and air
conditioner that are completely separate and each have a 24
VAC transformer for system control. These thermostats have a
“RC” terminal for cooling and a “RH” terminal for heating.
Connect the cooling unit red wire from the “R” terminal on the
outdoor unit to the “RC” terminal on the thermostat and the
RED air handler pigtail wire to the “RH” terminal on the
thermostat. Refer to Figures 21 - 28 for typical low voltage wire
connections.
If you have separate furnace and air conditioner with separate
transformers and your thermostat does not have the “RC” and
“RH” terminals it is recommended that you purchase a new
thermostat. If the furnace and air conditioner are both connected
to the thermostat “R” terminal it can cause transformer burnout
or it can cause either the furnace or air conditioner control
system to go into lockout.
Separate Heating and Cooling Units, Separate Thermostats
If the heating/cooling system in your house is a central heating
and cooling system but, the furnace and the cooling unit are
controlled by separate thermostats, then the use of a thermostat
interlock switch is required in order to prevent the furnace and
the air conditioner from operating at the same time.
Figure 21: Separate Thermostats; Separate Air
Handler and Cooling Unit
Figure 22: Separate Thermostats; Separate
Transformers, Separate Air Handler and Cooling Unit
Figure 23: Same Thermostat; Separate Air Handler,
Cooling Unit, and transformers
Do not locate thermostat within three feet of any of the following
items:
1 Furnace supply air registers
2 Cooling unit supply air registers
3 Lights or heat lamps
4 Aquariums
5 Televisions, stereo, amplifiers, surround sound systems
6 Stoves or any cooking appliance
7 Refrigerator
8 Washer and/or dryer
9 Hot water tank
10 Sink or near any hot water
11 Within 15 feet of any electric space heater
Within two feet of any sunlight
When using separate thermostats a thermostat interlock
system must be provided to prevent simultaneous operation
of the furnace and air conditioner. Simultaneous operation
can result in equipment overheating, equipment damage,
and wasted energy.
Do Not connect the Yellow wire to the thermostat unless an
outdoor unit is installed.
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