Sequence Of Operation; Emergency Heat Operation; Diagnostic Information - Trane ReliaTel Diagnostic Manual

Heat Pump Demand Defrost
calculate the new Initiate Value.
defrost cycle.

Sequence of Operation

Demand defrost is standard feature which permits defrost whenever coil icing conditions begin to
significantly reduce unit capacity. To permit defrost, the outdoor temperature must be below 52F ,
coil temperature must be below 33F , and the delta temperature F must exceed a RTRM calculated
value. After 30 minutes of run time under defrost permit conditions, the RTRM initiates a defrost
cycle. Upon termination of this cycle, the RTRM monitors the outdoor temperature (ODT) and the
coil temperature (CT) and calculates the delta temperature F (ODT-CT). This value is stored in
memory and the RTRM calculates a defrost initiate value. The RTRM continually compares the delta
temperature F to the defrost initiate value. Once the delta T reaches the initiate value, a defrost cycle
is initiated.
During the defrost cycle, the RTRM energizes the relay (K3), which energizes the switch over valve
(SOV) through the normally open K3 relay contact. This will then turn the outdoor fan motor(s)
(ODM) 'Off' by de-energizing the (K8) and (K7) relays, which de-energizes the (ODF) relays. The
RTRM energizes the auxiliary electric heat contactor (AH), and (BH) (if applicable), if they are not
operating, while maintaining compressor (CPR1) operation. The defrost cycle is terminated based
on the RTRM termination temperature calculation using the outdoor temperature (ODT) +47°F . The
defrost termination temperature (DTT) will be limited between 57°F and 72°F .

Emergency Heat Operation

When the system selection switch is in the 'EM HEAT' Mode, and the zone temperature falls below
the heating setpoint controlband, the RTRM bypasses compressor and outdoor fan operation and
energizes the K1 relay located on the RTRM. When K1 relay contacts close, the first stage auxiliary
electric heat contactor (AH) is energized. If the first stage of auxiliary electric heat cannot satisfy the
heating requirement, the RTRM energizes the K2 relay located on the RTRM.

Diagnostic Information

Demand Defrost also tracks failures and operating problems as follows:
When the K2 relay contacts close, the second stage auxiliary electric heat contactor (BH) is
energized. The RTRM cycles both the first and second stages of heat 'On' and 'Off' as required to
maintain the zone temperature setpoint.
Correct defrost operation relies on accurate temperature information from the outside air sensor
(OAS) and the coil temperature sensors (CTS).
If either of these sensors fail, the unit will revert to the default mode any time the unit is in the active
heat mode with compressors running.
When any Defrost Fault is active, or if any sensor has failed, a 5-minute defrost cycle will be initiated
after each 30 minutes of cumulative compressor heating operation.
94
Figure 56 presents a graphical representation of a typical demand
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