5285473-UIM-E-1217
Johnson Controls Unitary Products
15
NOTES:
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.
SECTION VI: OPERATION
The unit is controlled by a conventional heating/cooling thermostat.
If an electronic thermostat is used, make sure it has a common connec-
tion. DO NOT use a power stealing thermostat.
The unit has two stages of gas heat, and two stages of electric cooling.
The unit may be controlled using a single stage heat / single stage cool
(1H/1C) thermostat, but the second stage cooling is not available
unless the unit control is physically wired for full capacity cooling opera-
tion. For optimum performance, it is recommend to use a two stage
heat / two stage cool (2H/2C) thermostat.
HEATING SEQUENCE OF OPERATION
Heating
The control board begins a call for heat when W1 is energized (con-
nected to R).
The control checks to see if the pressure switch is open. If the pressure
switch is closed, the control board flashes “2” on the LED and waits
indefinitely for it to open. When the pressure switch is sensed as open,
the control begins pressure switch proving period. If the call for heat is
removed, the control goes back to Standby.
The unit control contains a built in 2
nd
stage heating “HI HEAT DELAY”
jumper that can automatically stage up to full capacity heating operation
based on first stage heating call timing. Built in heating stage up selec-
tion is a OFF, 10, 15, or 20 minute timer. Based on HI HEAT DELAY
jumper selection, the control is automatically staged up to high heat
during a call for low heat on the W1 input terminal. This timing starts
over with each new call for heat. Regardless of HI HEAT DELAY jumper
setting if anytime the control is operating in low heat (W1) and a 24 VAC
signal is received on the high heat input (W2), the control is staged up
to full capacity heating operation. When using the built in HI HEAT
DELAY feature and the control has staged up to full capacity heating,
the unit remains in full capacity heating until the call for heat on the W1
input is terminated. If using a two stage heating thermostat, set the HI
HEAT DELAY jumper to the OFF position.
Pressure Switch Proving
The control board energizes the induced draft motor and waits for the
pressure switch to close. When the pressure switch closes, the control
begins Pre-purge period. If the call for heat is removed, the control de-
energizes the inducer without post-purge and returns to standby.
If the pressure switch does not close within 5 seconds of inducer ener-
gizing, the control board flashes “3” on the LED. If the pressure switch
does not close within 60 seconds of inducer energizing, the control
shuts off the inducer for 60 seconds, then energizes the inducer for
another 60 seconds in an attempt to close the pressure switch. This
cycle continues indefinitely until either the pressure switch is proved
closed, or the call for heat ends.
Pre-purge
The control board monitors the pressure switch and ensures it remains
closed during pre-purge. If the pressure switch opens, the control goes
back to pressure switch proving mode. The control waits for a 15 sec-
ond pre-purge period, then begins the ignition trial.
Ignition Trial Period
The control board energizes the gas valve and spark outputs for a 5
second Ignition trial. The control de-energizes the spark when flame is
sensed and enters a flame stabilization period.
The unit control establishes flame in HI HEAT mode. If a call for heating
is only present on the first stage heating (W1) input, the control
switches to first stage heat after 10 seconds of flame. If there is a heat
call on the first and second stage input (W1 + W2), the control remains
in high heat mode.
If flame is not established within the ignition trial period, the control de-
energizes the spark and gas valve and begins an inter-purge period
before attempting another ignition trial.
If the call for heat is removed during an ignition trial period, the control
immediately de-energizes spark and gas. The control runs the inducer
motor through a post purge period before de-energizing.
If the pressure switch opens during an ignition trial period, the control
immediately de-energizes spark and gas. The control begins pressure
switch proving before an inter-purge and reignition attempt.
Table 12:
Additional Static Resistance
Size (Tons)
CFM
Wet Indoor Coil
Economizer
Filter/Frame Kit
036 (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
042 (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
048 (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
060 (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
