Rheem RQNM 13 Seer Series, Installation Instructions Manual

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2. In the heating mode, the first heat stage of the thermostat will energize one or
more supplementary resistance heaters. If required or considered desirable, the
resistance heat may also be controlled by outdoor thermostats. In the heating
mode, the thermostat will, on a call for heating, energize the indoor blower relay.
XVII. DEMAND DEFROST CONTROL AND
HIGH/LOW PRESSURE CONTROLS
The demand defrost control is a printed circuit board assembly consisting of solid
state control devices with electro-mechanical outputs. The demand defrost control
monitors the outdoor ambient temperature, outdoor coil temperature, and the com-
pressor run-time to determine when a defrost cycle is required.
Enhanced Feature Demand Defrost Control: Has high and low pressure control
inputs with unique pressure switch logic built into the microprocessor to provide
compressor and system protection without nuisance lock-outs. Cycles the compres-
sor off for 30 seconds at the beginning and end of the defrost cycle to eliminate the
increased compressor noise caused by rapidly changing system pressures when
the reversing valve switches. See the end of this section for diagnostic flash codes
for the two diagnostic LED’s provided on the control.
DEFROST INITIATION
A defrost will be initiated when the three conditions below are satisfied:
1) The outdoor coil temperature is below 35°F.
2) The compressor has operated for at least 34 minutes with the outdoor coil tem-
perature below 35°F.
3) The measured difference between the ambient temperature and the outdoor
coil temperature is greater than the calculated delta T.
Additionally, a defrost will be initiated if six hours of accumulated compressor run-
time has elapsed without a defrost with the outdoor coil temperature below 35°F.
DEFROST TERMINATION
Once a defrost is initiated, the defrost will continue until fourteen minutes has
elapsed or the coil temperature has reached the terminate temperature. The termi-
nate temperature is factory set at 70°F, although the temperature can be changed
to 50°F, 60°F, 70°F or 80°F by relocating a jumper on the board.
TEMPERATURE SENSORS
The coil sensor is clipped to the outdoor coil. The air sensor is located in the out-
door coil compartment.
If the ambient sensor fails the defrost control will initiate a defrost every 34 minutes
with the coil temperature below 35°F.
If the coil sensor fails the defrost control will not initiate a defrost.
TEST MODE
The test mode is initiated by shorting the TEST pins. In this mode of operation, the
enable temperature is ignored and all timers are sped up by a factor of 240. To initi-
ate a manual defrost, short the TEST pins. Remove the short when the system
switches to defrost mode. The defrost will terminate on time (14 minutes) or when
the termination temperature has been achieved. Short TEST pins again to termi-
nate the defrost immediately.
TROUBLE SHOOTING DEMAND DEFROST
Set the indoor thermostat select switch to heat and initiate a call for heat.
Jumper the “test pins” to put the unit into defrost. If the unit goes into defrost and
comes back out of defrost, the indication is that the control is working properly.
If the unit did not go into defrost using the test pins, check to ensure that 24V is
being supplied to the control board. If 24V is present then replace the control.
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