MORTEX
PRODUCTS
INC
FORT
WORTH,
TX
76106
Page
10
delay. The time delay relay contacts will close the circuit to
the isolation relay coil after the on- delay is complete. The
isolation relay normally open contacts (Terminals #2 and #4)
will close and the motor will operate on the selected speed tap
that has been placed on terminal #4.
When the thermostat is satisfied the circuit between “R”, “Y”
and “G” will open. The time delay relay will open the circuit
to the isolation relay and the PSC blower motor will turn off.
The X-13 blower motor will have a 13 second off-delay. The
blower is now in the standby mode waiting for the next
cooling cycle
The Heating Cycle
When the thermostat is in the HEAT mode and the fan switch
on the thermostat is set to AUTO. The call for heat closes the
thermostat circuit between the “R” and “W” terminals. 24
VAC is sent from the “W” terminal, through the white
thermostat wire to the white pigtail wire on the furnace. 24
VAC is sent through the white pigtail wire to the 24 VAC coil
on the first heater relay. This signal energizes the heater relays
closing the contacts to the heaters. The blower low speed wire
is also connected to the first heater relay so the blower is
energized at the same time as the heater. The blower will
continue to operate until the thermostat is satisfied. When the
call for heat has been removed the “W” terminal is de-
energized and the heater relay opens turning off the heater and
the PSC blower motor. The X-13 blower motor will have a 13
second off-delay. The furnace is now in standby mode waiting
for the next heating cycle.
Some models have a black pigtail wire that is connected to the
24 VAC coil on the second heater relay. This pigtail wire is to
be used for second stage heat. It is connected to the thermostat
“W2” terminal. You must have a thermostat that has the
second stage heating feature “W2”. The second stage heat
cycle is enabled when the room temperature typically falls
more than 3 degrees below the thermostat set point. The
thermostat energizes the second heater to aid in heating the
room back to the thermostat set point. Once the room is within
1 degree of the thermostat set point the second stage heater is
de-energized until the thermostat calls for second stage heat
“W2” again.
The Cooling Cycle
When the thermostat calls for cooling
The thermostat closes the circuit between the “R”, “Y” and
“G” terminals. 24 VAC is sent from the “Y” terminal through
the yellow thermostat wire to the 24 VAC coil terminal on the
condenser contactor; energizing the contactor and starting the
compressor and outdoor fan motor. At the same time the “G”
terminal is sending 24 VAC through the green pigtail wire to
the indoor blower time delay relay. The time delay relay goes
through an 0-30 second on-delay, and then closes the contacts
sending 24 VAC to the isolation relay coil ( Terminals #1 and
#3). The isolation relay coil is energized closing the normally
open contacts (Terminals #2 and #4) and opening the normally
closed contacts (Terminals #5 and #6) sending 24 VAC to the
selected X-13 motor speed tap wire connected to isolation
relay terminal #4 or for PSC motors; sending 240 VAC to the
selected speed tap wire connected to isolation relay terminal
#4.
When the thermostat call for cooling has been satisfied the
thermostat opens the circuit between the “R”, “Y” and “G”
terminals. The 24 VAC signal is removed from the thermostat
“Y” terminal de-energizing condenser contactor. At the same
time the “G” terminal 24 VAC is removed from the green
pigtail wire de-energizing the TDR. The X-13 motor goes
through a 13 second off delay; then stops. The PSC motor
does not have a delay; so it stops. The cooling cycle is
complete, and the cooling unit is ready for the start of the next
cooling cycle.
The Motor Isolation Relay
This relay is used in conjunction with the motors to prevent
the possibility of the motors being energized on two speed
taps at the same time. This condition would burn out the motor
windings.
A black wire is connected from the circuit breaker to the
supply side of the normally open terminals on the relay. The
blower motor high speed tap wire is connected to the load side
(Terminal #4) normally open terminal on relay.
A red wire is connected from the heat relay to the normally
closed terminal on the relay. The load side (Terminal #6) of
the normally closed terminal is connected to the low speed tap
blower motor.
Figure 10: Motor Speed Tap Isolation Relay
For personal safety be sure to turn the electrical power
“OFF” at the main entrance (Circuit Breaker Box) and at the
control box circuit breakers before attempting any service or
maintenance operations. Home owners should never attempt
to perform any maintenance which requires opening the
furnace control box door.
