Demand Defrost Control; Defrost Initiation; Defrost Termination; Temperature Sensors - Reelin PNE 13 Seer Installation Instructions Manual

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8.0 DEMAND DEFROST CONTROL

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.
Standard Defrost Control (part number 47-21517-16): Found in units with model
numbers ending in "BZ".
Enhanced Feature Demand Defrost Control (part number 47-21517-22): Found
in units with model numbers ending in "AZ" and units equipped with the field
installed Enhanced Compressor Protection Kit (RXPG-A01). Has high and low
pressure control inputs with unique pressure switch logic built into the microproces-
sor to provide compressor and system protection without nuisance lock-outs.
Cycles the compressor off for 5 seconds and the beginning and end of the defrost
cycle to eliminate the increased compressor noise caused by rapidly changing sys-
tem pressures when the reversing valve switches. See section 8.7 for diagnostic
flash codes for the two diagnostic LED's provided on the control.

8.1 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.

8.2 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.

8.3 TEMPERATURE SENSORS

The coil sensor is clipped to the top tube on the outdoor coil at the point feed by the
distribution tubes from the expansion device (short 3/8" dia. tube). The air sensor is
located on the defrost control board.
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.

8.4 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.

8.5 TROUBLE SHOOTING DEMAND DEFROST

Set the indoor thermostat select switch to heat and thermostat lever to 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.