Operating instructions

14E. REVERSING VALVE

The reversing valve is the heart of a heat pump. It directs

refrigerant flow to the coils to achieve proper direction of

flow that allows the same system to supply heated or

cooled air to enter the inside atmosphere of the structure

according to occupants' desires.

The reversing valve's solenoid can be energized in

either HEAT or COOL mode of operation. Duo-Therm Heat

Pumps that are roof-mounted units have the solenoid

energized in the COOL mode of operation.

One way to check the reversing valve is to feel the

refrigerant line at the top of the inside coil. In the COOL

mode, this line will be cool or cold to the touch. In the HEAT

mode, this line will be warm or hot to the touch. If you do not

achieve these results, direction of refrigerant flow is not

correct. Check the relay (see Section 4.10), wiring (see

Section 2.3) and thermostat (see Section 4.2). Refer to

Section 1 for Principals of Heat Pump Operation.

The ohms resistance of the reversing valve solenoid coil

is approximately 465 ohms plus or minus (±) 10%.

15E. RELAY, FAN SPEED (DPST)

The relay is a double pole, single throw and controls the fan

motor in the roof mounted unit. When the AUX HEAT mode

is selected or the outside temperature is too cold for HEAT

PUMP operation and automatically goes to auxiliary opera-

tion, the relay will interrupt the circuit to the fan motor.

When COOL, OFF and HEAT PUMP modes are se-

lected, the relay coil is not energized. When AUX. HEAT

mode is selected the relay coil is energized with 12V DC.

To check the relay, first remove the wires from COM

and NC terminals. Next verify the relay coil is not energized

(no DC power), continuity should exist between terminals

COM and NC and no continuity between terminals COM

and NO. Next energize the relay coil with DC volts (10 to

16). Continuity should exist between terminals COM and

NO and no continuity between COM and NC. If the above

checks are correct, the relay is good – DO NOT replace it.

If the above checks are not correct, the relay is defective

and should be replaced.

NOTE: Verify the thermostat is wired properly from the

furnace, as incorrect polarity on the furnace thermostat

wires will energize the relay coil and keep the fan motor

from operating in the roof mounted unit.