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292447-YIM-A-0507
46 Unitary Products Group
Compressor Protection
In addition to the external pressure switches, the compressors
also have inherent (internal) protection. If there is an abnormal
temperature rise in a compressor, the protector will open to shut
down the compressor. The UCB incorporates features to
minimize compressor wear and damage. An Anti-Short Cycle
Delay (ASCD) is utilized to prevent operation of a compressor
too soon after its previous run. Additionally, a minimum run time
is imposed any time a compressor is energized.
The ASCD is initiated on unit start-up and on any compressor
reset or lock-out.
Flash Codes
The UCB will initiate a flash code associated with errors within
the system. Refer to UNIT CONTROL BOARD FLASH CODES
Table 30.
Reset
Remove the call for cooling, by raising thermostat setting higher
than the conditioned space temperature. This resets any
pressure or freezestat flash codes.
Reheat Mode Sequence Of Operation
The reheat control board allows the user to select two different
modes of operation via a jumper connection on the board. (See
Figure 31.) Each mode is described below.
“Normal” Mode
When the reheat control board (RCB) detects a need for
dehumidification (24VAC) at "HUM" via the field supplied
dehumidistat connected to RHTB-1 and RHTB-2 and there is
not a call for cooling, it energizes the hot gas relay (HGR),
which energizes the 3-way valve (SOL 3), the condenser coil
valve (SOL 2), and de-energizes the reheat coil bleed valve
(SOL 1). (In the ZR150, SOL 2 is only energized when the
discharge pressure in circuit #1 rises above 400 psig and de-
energizes SOL 2 after the discharge pressure falls below 320
psig. Both outdoor fans of circuit #1 in the ZR150 also
disengage to conserve energy.) The Y1 signal is passed to the
unit control board (UCB), which engages circuit # 1, resulting in
circuit #1 reheat mode operation.
When the room thermostat calls for first stage cooling, with or
without a call for dehumidification, the RCB senses a signal
through "Y1", de-energizing the HGR, which de-energizes SOL
3 and SOL 2 and energizes SOL 1, engaging circuit #1,
resulting in circuit #1 cooling mode operation.
When the room thermostat calls for second stage cooling, the
RCB senses a signal through "Y1" & "Y2" and engages circuit
#1 and circuit #2 in cooling mode.
Indoor blower operation is initiated upon a call for first stage
cooling, second stage cooling or dehumidification.
Anytime there is a call for 2 stages of cooling, the unit will not
operate in the reheat mode, even if there is a call for
dehumidification at "HUM".
The unit will not operate in the reheat mode if there is any call
for heating.
On units with economizers, the unit will not operate in the
reheat mode if there is a call for cooling and the economizer is
operating as first stage of cooling.
All safety devices function as previously described.
"Alternate” Mode
When the RCB detects a need for dehumidification (24VAC) at
"HUM" via the field supplied dehumidistat connected to RHTB-1
and RHTB-2, and there is not a call for cooling, it energizes the
HGR, which energizes the SOL 3, SOL 2, and de-energizes
SOL 1. (In the ZR150, SOL 2 is only energized when the
discharge pressure in circuit #1 rises above 400 psig and de-
energizes SOL 2 after the discharge pressure falls below 320
psig. Both outdoor fans of circuit #1 in the ZR150 also
disengage to conserve energy.) The unit then operates with
circuit #1 in reheat mode and circuit #2 in cooling mode.
When the room thermostat calls for first stage cooling while
there is still a call for dehumidification, no operational change is
made. The call for cooling is ignored and the unit continues to
operate with circuit #1 in reheat mode and circuit #2 in cooling
mode.
When the room thermostat calls for second stage cooling, the
RCB senses a signal through "Y1" and "Y2" and de-energizes
the HGR, which de-energizes SOL 3 and SOL 2, and energizes
SOL 1. Both circuits operate in the cooling mode.
Indoor blower operation is initiated upon a call for first stage
cooling, second stage cooling or dehumidification.
Anytime there is a call for 2 stages of cooling, the unit will not
operate in the reheat mode, even if there is still a call for
dehumidification at "HUM".
The unit will not operate in the reheat mode if there is any call
for heating.
All safety devices function as previously described.