York TM8V C Series Installation Manual page 27

LIMIT CONTROLS
There is a high temperature limit control located on the furnace vesti-
bule panel near the gas valve. This is an automatic reset control that
provides over temperature protection due to reduced airflow. This may
be caused by:
1. A dirty filter.
2. If the indoor fan motor should fail.
3. Too many supply or return registers closed or blocked off.
The control module will lockout if the limit trips 5 consecutive times. If
this occurs, control will reset & try ignition again after 1 hour.
SEQUENCE OF OPERATION
Heating and Cooling Airflow
The heating and the cooling airflows are preset at the factory. The heat-
ing airflow is set to the maximum CFM. The cooling airflow is set to pro-
vide 90 percent of the maximum CFM. The heating and cooling airflows
must be field adjusted to match the HVAC system at installation. See
Table 14 for the HEAT, COOL and ADJ jumper settings to use for spe-
cific airflows.
CFM Board - Delay Taps Selection
The set of jumper pins on the control board labeled DELAY are used to
set the delay profiles for the furnace. These can be chosen so as to
maximize the comfort and sound levels for various regions of the coun-
try.
Tap A is the default profile. It provides a 30-second ramp-up from zero
airflow to full capacity and a 30-second ramp-down from full capacity
back to zero airflow. Whenever there is a change in airflow mode, such
as from low heat to high heat, the motor will take 30 seconds to ramp
from one speed to the other.
Tap B is the humid profile. This profile is best-suited for installations
where the humidity is frequently very high during cooling season, such
as in the southern part of the country. On a call for cooling, the blower
will ramp up to 50% of full capacity and will stay there for two minutes,
then will ramp up to 82% of full capacity and will stay there for five min-
utes, and then will ramp up to full capacity, where it will stay until the
wall thermostat is satisfied. In every case, it will take the motor 30 sec-
onds to ramp from one speed to another.
Tap C is the dry profile. This profile is best suited to parts of the country
where excessive humidity is not generally a problem, where the sum-
mer months are usually dry. On a call for cooling the motor will ramp up
to full capacity and will stay there until the thermostat is satisfied. At the
end of the cooling cycle, the blower will ramp down to 50% of full capac-
ity where it will stay for 60 seconds. Then it will ramp down to zero. In
every case, it will take the motor 30 seconds to ramp from one speed to
another.
Tap D is the normal profile, best suited for most of the country, where
neither excessive humidity nor extremely dry conditions are the norm.
On a call for cooling, the motor will ramp up to 63% of full capacity and
will stay there for 90 seconds, then will ramp up to full capacity. At the
end of the cooling cycle, the motor will ramp down to 63% of full capac-
ity and will stay there for 30 seconds, then will ramp down to zero. In
every case, it will take the motor 30 seconds to ramp from one speed to
another.
Continuous Blower Operation
The blower will run continuously whenever the wall thermostat fan
switch is in the ON position. The furnace blower will run at the speed
selected on the FAN SPEED jumpers on the main control board
(HI COOL, LO COOL, HI HEAT or LO HEAT). When the jumper is in the
VS G position, the blower will run at 50% of the high cool speed.
Johnson Controls Unitary Products
Intermittent Blower Cooling
On cooling/ heating thermostats with a fan switch, when the fan switch
is set in the auto position and the thermostat calls for cooling, a circuit is
completed between the R, Y and G terminals. The motor is energized
through the Y1 cool terminal and runs on the speed selected on the
COOL tap of the control board. The fan off setting is fixed at 60 seconds
for SEER enhancement. The control board can accommodate two-
stage cooling. When a two-stage cool thermostat is connected to the Y1
and Y2 terminals on the board, the blower will operate on LOW COOL
speed when Y1 is energized and on HI COOL speed when Y1 and Y2
are energized.
Intermittent Blower Heating
On cooling/ heating thermostats with a fan switch, when the fan switch
is set in the auto position and the thermostat calls for heating, a circuit is
completed between the R and W terminals. The indoor fan motor runs
on the speed selected on the HEAT tap of the control board.
Humidistat
When a humidistat is installed in the system, the "Humidistat Installed?"
jumper on the control board should be moved to the YES position.
The cooling CFM will then be reduced by 15% whenever the humidistat
indicates high humidity.
Hot Surface Ignition System
WARNING
!
HOT SURFACE IGNITION SYSTEM
Do not attempt to light this furnace by hand (with a match or any other
means). There may be a potential shock hazard from the components
of the hot surface ignition system. The furnace can only be lit auto-
matically by its hot surface ignition system.
TROUBLESHOOTING
The following visual checks should be made before troubleshooting:
1. Check to see that the power to the furnace and the ignition control
module is ON.
2. The manual shut-off valves in the gas line to the furnace must be
open.
3. Make sure all wiring connections are secure.
4. Review the sequence of operation. Start the system by setting the
thermostat above the room temperature. Observe the system's
response. Then use the troubleshooting section in this manual to
check the system's operation.
WARNING
!
Never bypass any safety control to allow furnace operation. To do so
will allow furnace to operate under potentially hazardous conditions.
Do not try to repair controls. Replace defective controls with UPG
Source 1 Parts.
Never adjust pressure switch to allow furnace operation.
FURNACE CONTROL DIAGNOSTICS
The furnace has built-in, self-diagnostic capability. A blinking LED light
on the control board can flash red, green or amber to indicate various
conditions. The control continuously monitors its own operation and the
operation of the system. If a failure occurs, the LED light will indicate
the failure code.
The SLOW flash speed is two seconds on and two seconds off.
The other flash codes listed below have the following timing: LED light
will turn on for 1/3 second and off for 1/3 second. This pattern will be
repeated the number of times equal to the code. There will be a two-
second pause between codes. For example, the six red flash code will
flash the LED light on and off six times, then will be off for two seconds.
This pattern will repeat as long as the fault condition remains. The con-
tinuous flash codes listed below will flash the LED light on and off con-
tinuously, with no breaks or longer pauses.
5402847-UIM-A-0917
27