246824-YTG-G-1208
Johnson Controls Unitary Products
13
•
PROPANE CONVERSION KIT
– Contains new orifices
and gas valve springs to convert from natural to L.P. gas.
•
60ºF GAS HEAT KIT
– Provides an electric heat kit for the
gas compartment for use in extreme low ambient
conditions.
•
ECONOMIZER
(Downflow and Horizontal flow)
•
POWER EXHAUST
– (Unit mount – Downflow, Duct
mount – Horizontal flow)
•
DUAL ENTHALPY KIT
- Provides a second input to
economizer to monitor return air.
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 3.) Each mode is described below.
“NORMAL” MODE
When the reheat control board (RCB) detects a need for dehu-
midification (24VAC) at "HUM" via the field supplied dehumidis-
tat 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 opera-
tion.
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, result-
ing 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 dehumidi-
fication 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 dis-
charge pressure in circuit #1 rises above 400 psig and de-ener-
gizes 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 dehu-
midification 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.
