![background image](http://html1.mh-extra.com/html/york/20-series/20-series_installation-manual_4665513050.webp)
349215-JIM-B-1008
50
Johnson Controls Unitary Products
supply air flow occurs, thus shutting down the
heater and energizing the blower.
2. Temperature Limit Switch (TLS 3, 4, 5 and 6).
This control is located inside the heater compart-
ment and is set to open at the temperature indi-
cated in the Limit Control Setting Table 22. It is a
manual reset limit. These limit switches will de-
energize the heaters should the primary limit fail to
open or the contactors fail to open in a failure
mode.
FLASH CODES
The UCB will initiate a flash code associated with
errors within the system. Refer to UNIT CONTROL
BOARD FLASH CODES Table 27.
RESET
Remove the call for heating by lowering the thermostat
setting lower than the conditioned space temperature.
This resets any flash codes.
HEAT ANTICIPATOR SETPOINTS
It is important that the anticipator setpoint be correct.
Too high of a setting will result in longer heat cycles
and a greater temperature swing in the conditioned
space. Reducing the value below the correct setpoint
will give shorter "ON" cycles and may result in the low-
ering of the temperature within the conditioned space.
Refer to Table 23 for the required heat anticipator set-
ting.
GAS HEATING SEQUENCE OF OPERATIONS
The following sequence describes the operation of the
gas heat section.
When the thermostat calls for the first stage of heating,
the low-voltage control circuit from "R" to "W1" and "G"
is completed, thru the UCB. The heat relay "RW1" is
energized. The "RW1-2" contacts close energizing the
draft motor control. The draft motor control contacts
close and start the draft motor. As the speed of the
draft motor reaches approximately 2500 RPM, the cen-
trifugal switch contact, located on the end of the draft
motor shaft, closes to power the first stage ignition
module "IC1", thru the "RW1-1 contacts.
Ignition module "IC1" will immediately start the first
stage igniter sparking and will open the redundant
valve located inside the first stage main gas valve
"GV1" to allow a flow of gas to only the first stage carry-
over tube. Only after the pilot flame has been ignited
and the presence of pilot flame detected at the "IC1" by
a signal sent back through the flame sensor is sparking
terminated and the first stage main gas valve opened.
TABLE 22: LIMIT CONTROL SETTING
18
36
54
72
18
36
54
72
18
36
54
72
18
36
54
72
TEMPERATURE LIMIT
SWITCH 1, 2
OPENS,
0
F
TEMPERATURE LIMIT
SWITCH 3, 4, 5, 6
OPENS,
0
F
UNIT
(Tons)
VOLTAGE
HEATER
kW
120
170
120
170
120
170
120
170
140
200
140
200
140
200
140
200
120
120
120
120
120
120
120
120
170
170
170
170
~
~
~
~
15
17.5, 20,
25
15,17.5,
20, 25
240
240
460
600
15,17.5,
20, 25
TABLE 23: ELECTRIC HEAT ANTICIPATOR
SETPOINTS
HEATER
KW
VOLTAGE
SETTING, AMPS
TH1
TH2
18
208/230-3-60
0.29
-
36
0.29
0.29
54
0.29
0.58
72
0.29
0.58
18
460-3-60
0.29
-
36
0.29
0.29
54
0.29
0.29
72
0.29
0.29
18
575-3-60
0.29
-
36
0.29
0.29
54
0.29
0.29
72
0.29
0.29
For units with VFD and gas heat, the speed of
the indoor blower motor continues to be con-
trolled by duct static pressure via the VAV con-
trol board.
If there are VAV boxes present in the duct sys-
tem, the boxes must be driven to the full-open
position using a customer-supplied power
source to assure adequate airflow across the
heat exchanger tubes.