1-8
Clutch Relay (CR)
The Clutch Relay (CR) is located in the electrical
control panel. When the CR relay is energized, a set of
internal contacts will close to engage the compressor
clutch (CL) to start the refrigerant cycle.
Air Conditioning Relay (ACR)
The Air Conditioning Relay (ACR) is located in the
electrical control panel. The ACR relay is energized
when the A/C Switch (ACS) is placed in the COOL
position. When the ACR relay is energized, a set of
normally open ACR contacts will close to allow the
Clutch Relay (CR) and Condenser Fan Relay (CFR1) to
energize. When de-energized, the ACR relay will prevent
the clutch and condenser fans from being activated
during the heating mode of operation.
Heat Relay (HR)
The Heat Relay (HR) is located in the electrical
control panel. This relay will energize only when the A/C
Switch (ACS) is in the HEAT position. When energized,
a set of normally open HR contacts will close to allow the
thermostat to control operation of the Boost Pump Relay
(BPR) and Reheat Coolant Valve (RCV) during the
heating mode. When the thermostat calls for heating,
power is applied from thermostat plug J1, pin 1, through
the closed HR contacts to energize the Boost Pump Relay
(BPR) and Reheat Coolant Valve (RCV) and start the
flow of engine coolant for heating.
Heat Relay #2 (HR2)
The Heat Relay #2 (HR2) is located in the electrical
control panel. This relay is energized during the cooling
cycle mode (when the thermostat is calling for cooling)
and during the cooling with reheat mode (when the
thermostat is calling for cooling only) to prevent the
heating circuit from being energized while in cooling
operation. The relay is de-energized during the cooling
with reheat mode to activate the heating control circuit
when the thermostat is not calling for cooling.
With the ACS switch in the COOL position and the
RHCS switch in the CYCLE or REHEAT position, and
when the thermostat calls for cooling, power is applied
from the thermostat plug no. J1, pin no. 3, to energize
Heat Relay #2 (HR2). Energizing relay HR2 opens a set
of normally closed HR2 contacts to prevent activation of
the heating control circuit while unit is in the cooling cycle
mode.
With the ACS switch in the COOL position and the
RHCS switch in the REHEAT position, and when the
thermostat is not calling for cooling, power is removed
from thermostat plug J1, pin no. 3, to de-energize Heat
Relay #2 (HR2). De-energizing relay HR2 closes a set of
normally closed HR2 contacts to activate the heating
control circuit enabling the system to provide heating
during the cooling with reheat mode.
Evaporator Fan Relay #1 (EFR1)
Evaporator Fan Relay #1 (EFR1) is located in the
electrical control panel. When the Air Conditioning
Switch (ACS) is placed in either the COOL or HEAT
position, EFR1 relay is energized. When energized, a set
of internal EFR1 contacts are closed to start Evaporator
Fan Motors (EM1 and EM2).
Evaporator Speed Relays #1 and #2 (ESR1 and ESR2)
The Evaporator Speed Relays (ESR1 and ESR2) are
located in the electrical control panel. These relays will
only energize when the A/C Switch (ACS) is in the HEAT
position. When energized, normally closed ESR1 and
ESR2 contacts will close to start low speed evaporator fan
motor operation.
Condenser Fan Relay #1 (CFR1)
The Condenser Fan Relay #1 (CFR1) is located in
the electrical control panel. When the A/C Switch (ACS)
is placed in the COOL position, A/C Relay (ACR) is
energized closing a set of normally open ACR1 contacts.
And, when the thermostat calls for cooling, power is
applied to thermostat plug J1, pin no. 3, to energize
CFR1 relay through the closed ACR1 contacts. When
energized, a set of normally open CFR1 contacts close to
start the Condenser Fan Motors (CM1, CM2 and CM3).
The Low Ambient Thermostat (LATH) and Freeze
Thermostat Switches (FTS), if installed, must also be
closed to energize the Condenser Fan Relay.
Condenser Speed Relay (CSR)
The Condenser Speed Relay (CSR) is located in the
electrical control panel. This relay is energized at the
same moment the Condenser Fan Relay is energized
provided the Condenser Fan Speed Switch (CSR) is
closed. When energized, the CSR relay will open a set of
normally closed CSR1 contacts to operate condenser
fans on low speed. If the condenser coil pressure reaches
the CFS switch cutout setting, the CFS switch will open to
de-energize the Condenser Speed Relay (CSR).
De-energizing the CSR relay will close a set of normally
closed CSR1 contacts enabling the Condenser Fan
Motors (CM1, CM2 and CM3) to operate on high speed.
Boost Pump Relay (BPR)
The Boost Pump Relay (BPR) is located in the
electrical control panel. This relay is energized during
heating. When the Boost Pump Relay (BPR) is
energized, a set of normal open BPR contacts will close to
activate the Boost Pump Motor (BPM).
Low Voltage Cutout (LVCO)
The Low Voltage Cutout (LTCO) is located in the
electrical control panel. If this relay detects a low voltage
condition, LVCO contacts will open to de-energize
Clutch Relay (CR), which disengages the clutch.
