5322625-UIM-A-0417
Johnson Controls Unitary Products
17
SECTION VI: OPERATION
The unit is controlled by a dual fuel thermostat. If an electronic thermo-
stat is used, make sure it has a common connection. DO NOT use a
power stealing thermostat.
This unit has a multi-stage compressor, therefore the unit has two
stages of mechanical heat, and two stages of mechanical cooling. For
optimum performance, it is recommend to use a four stage heat / two
stage cool (4H/2C) heat pump dual fuel thermostat.
COOLING SEQUENCE OF OPERATIONS
A call for a compressor cooling signal from the thermostat is initiated at
the “Y1” terminal (for OD compressor) and the “O” terminal (for revers-
ing valve).
The control cycles the compressor and indoor blower to second stage
cooling speed anytime a second stage cooling “Y2” call is received
during a first stage cooling “Y1” call. The control does not operate on
second stage cooling without a call on the “Y2” thermostat input.
1.
On a call for cooling, the thermostat sends 24 volts to “Y” and “O” on
the defrost control board. The reversing valve solenoid is energized.
After the anti-short cycle delay (ASCD) period is complete, the con-
tactor coil “M” is energized. Power is supplied to the compressor and
outdoor fan motor, and the reversing valve is switched to the cooling
position. The indoor blower is controlled by the indoor blower control
board. It operates on the “LOW COOL” or “HIGH COOL” speed
based on the 24 VAC input from the defrost control board. If the con-
trol receives an “O” input without a “Y” input, it energizes the revers-
ing valve only.
2.
When the demand for cooling has been satisfied, the 24 volt “Y”
signal is removed, and the contactor is de-energized. The indoor
blower motor continues to run and ramps down after a 60 second
delay.
Dehumidification/Humidity Switch Input
This model unit features a built in de-humidification feature for
advanced dehumidification during cooling operation. The unit indoor
blower control is designed to work with a humidity control that closes
when the humidity is below the set-point. The control is open when the
humidity is above the set-point. This humidity control may be referred to
as a humidistat or dehumidistat.
To use this feature, the control HUM STAT jumper must be set to YES
and a humidistat is connected from the low voltage R and HUM color
coded leads. During cooling operation if the humidity level is above the
humidistat set point, the indoor blower speed is reduced by approxi-
mately 15%.
Safety Controls
The control circuit includes the following safety controls:
High Pressure Switch (HPS) -
The switch protects against excessive
discharge pressures. If system pressures exceed 650 psi, the defrost
control locks out compressor operation.
Loss of Charge Switch (LCS) -
The switch protects against loss of
charge due to a leak in the system.
Table 13:
Additional Static Resistance
Size (Tons)
CFM
Wet Indoor Coil
Economizer
1
1. The pressure drop through the economizer is greater for 100% outdoor air
than for 100% return air. If the resistance of the return air duct is less than
0.25 IWG, the unit will deliver less CFM during full economizer operation.
Filter pressure drop based on standard filter media tested at velocities not
to exceed 300 ft/min.
Filter/Frame Kit
24 (2.0)
500
0.01
0.00
0.01
600
0.01
0.00
0.02
700
0.01
0.00
0.04
800
0.02
0.01
0.06
900
0.03
0.01
0.08
1000
0.04
0.01
0.10
1100
0.05
0.01
0.13
1200
0.06
0.02
0.16
30 (2.5)
700
0.01
0.00
0.04
800
0.02
0.01
0.06
900
0.03
0.01
0.08
1000
0.04
0.01
0.10
1100
0.05
0.01
0.13
1200
0.06
0.02
0.16
1300
0.07
0.03
0.17
36 (3.0)
700
0.01
0.00
0.04
800
0.02
0.01
0.06
900
0.03
0.01
0.08
1000
0.04
0.01
0.10
1100
0.05
0.01
0.13
1200
0.06
0.02
0.16
1300
0.07
0.03
0.17
1400
0.08
0.04
0.18
42 (3.5)
1100
0.02
0.02
0.04
1200
0.03
0.02
0.04
1300
0.04
0.02
0.05
1400
0.05
0.03
0.05
1500
0.06
0.04
0.06
1600
0.07
0.04
0.07
1700
0.07
0.04
0.08
1800
0.08
0.04
0.09
1900
0.09
0.05
0.10
2000
0.09
0.05
0.11
48 (4.0)
1100
0.02
0.02
0.04
1200
0.03
0.02
0.04
1300
0.04
0.02
0.05
1400
0.05
0.03
0.05
1500
0.06
0.04
0.06
1600
0.07
0.04
0.07
1700
0.07
0.04
0.08
1800
0.08
0.04
0.09
1900
0.09
0.05
0.10
2000
0.09
0.05
0.11
60 (5.0)
1100
0.02
0.02
0.04
1200
0.03
0.02
0.04
1300
0.04
0.02
0.05
1400
0.05
0.03
0.05
1500
0.06
0.04
0.06
1600
0.07
0.04
0.07
1700
0.07
0.04
0.08
1800
0.08
0.04
0.09
1900
0.09
0.05
0.10
2000
0.09
0.05
0.11
NOTICE
This unit REQUIRES the use of a thermostat to control fossil fuel
(dual fuel) operation.
WARNING
The ability to properly perform maintenance on this equipment
requires certain expertise, mechanical skills, tools and equipment. If
you do not possess these, do not attempt to perform any mainte-
nance other than those procedures recommended in this Installation
Manual. Failure to heed this warning could result in serious injury
and possible damage to this equipment.
!
