90% Limit Switch
Tripping
Model and serial
number of the furnace
Model number __________________________________
Serial number
__________________________________
Control Board Part Number
________________________
Model Plug Part Number __________________________
Note: If the control was replaced from
another unit, the model
plug may be the wrong part number for
this model furnace.
58 Series furnaces: Refer to unit
wiring diagram
59 Series furnaces: Refer to unit
rating plate
Model and serial number
of the "N" coil
Model number __________________________________
Serial number
__________________________________
Model and serial
number of the outdoor unit
Model number __________________________________
Serial number __________________________________
Does the limit trip
in (circle as many as applies)
What is the
temperature rise in:
Low heat Medium
heat High heat
Is a by-pass
humidifier installed?
Manifold pressure
set with burner box cover off?
Remember: for natural gas on Step Modulating furnaces manifold pressure
is set as follows: Medium heat, high heat then low heat.
Is this a propane
installation?
For propane on Step Modulating furnaces manifold pressure is set as
follows: high heat, medium heat then low
heat
For variable speed
airflow selections, refer to the appropriate box below. Airflow selection
methods for Infinity/Evolution systems are different than the method for
variable speed furnaces controlled by a thermostat.
If the furnace is
controlled by a User Interface, do a complete re-install or perform a duct
assessment. Note what the duct system static pressure is. If the static
pressure is over 1.00 esp, look for restrictions or obstructions in the duct
system such as:
Dirty filter
|
High pressure
drop filter
|
Dirty evaporator
coil
|
Dirty condensing
heat exchanger coil
|
Supply dampers
closed
|
Zone dampers
wired backward
|
Supply registers
closed or blocked
|
Return grills
blocked
|
Air Flow
Adjustments:
Is this an Infinity/Evolution
System?
Note: Do not make any
changes at the furnace control board. All furnace options are configured at
the User Interface.
Was the airflow
setting on the U.I. changed from
"Comfort" to "Efficiency"?
This will increase the airflow in certain modes, depending on the type
of furnace. See Note: below.
Note: On 2 stage VSP models, when the Comfort/Efficiency setting is changed
to “Efficiency”, All models
(except the 40,000 BTUH model) the Low Heat airflow is increased by 7 percent
and High Heat airflow is increased 8 percent for maximum comfort. On 40,000
BTUH models the Low Heat airflow will increase by 11 percent and High Heat
airflow is increased 10 percent. Factory default setting is “Comfort” at the
U.I. or “ON” at the furnace control.
Note: On Step Modulating
models,
when the Comfort/Efficiency
setting is changed to “Efficiency”,
Low Heat airflow is increased by 9 percent, Medium Heat airflow is increased
by 7 percent and High Heat airflow is increased 15 percent for maximum
efficiency.
Is the Low Heat Rise or Low/Med Heat Rise setting on the U.I. turned “ON”?
This will increase the airflow in certain modes, depending on the type
of furnace. See Note: below.
Note: When the Low Heat Rise or Low/Med Heat
Rise is turned “ON”, it increases
Low Heat (2 stage VSP models) airflow or Low and Medium Heat (Step Mod
models) airflow by 18 percent. This compensates for increased return air
temperature from bypass humidifiers.
The
maximum airflow increase when the U.I.
is set for “Efficiency” and the Low Heat Rise (or Low/Medium Heat Rise) is turned “ON” is:
For 2-stage models, 18% in Low
Heat
8%
in High Heat (10% for 40,000 BTUH models)
For Step-Modulating Models, 18% in
Low Heat
18% in Medium Heat
15% in High Heat
|
Is this a
variable speed furnace on a non-Infinity/Evolution System?
Is the Comfort/Efficiency, SW 1-4 switch
turned “OFF” at the furnace control?
This will increase the airflow in certain modes, depending on the type
of furnace. See Note: below.
Note: On 2
stage VSP models, when SW 1-4 is
turned “OFF”, Low Heat
airflow is increased by 7 percent
and High Heat airflow is increased 8
percent for maximum comfort. On 040
units the Low Heat airflow will
increase by 11 percent and High
Heat airflow is increased 10 percent.
Factory default setting is
“Comfort” at the U.I. or “ON” at the furnace
control.
Note: On Step
Modulating models, when SW 1-4 is turned “OFF”, Low
Heat airflow is increased by 9
percent, Medium Heat airflow is increased by
7 percent and High Heat airflow is
increased 15 percent for maximum
efficiency.
Is the Low Heat Rise switch, SW 1-3 turned
“ON” at the furnace control?
This will increase the airflow in certain modes, depending on the type
of furnace. See Note: below.
Note: When
SW 1-3 is turned “ON”, it increases Low Heat (2 stage VSP
models) airflow or Low and Medium
Heat (Step Mod models) airflow by 18
percent. This compensates for
increased return air temperature from
bypass humidifiers.
The
maximum airflow increase when SW1-4
is turned “OFF” and SW1-3 is turned “ON”
is:
For 2-stage models, 18% in Low
Heat
8% in High Heat (10% for 40,000 btuh models)
For Step-Modulating Models, 18% in Low
Heat
18% in Medium Heat
15% in High Heat
|
Increase the blower off delay time. The limit may be tripping
after the call for heat has terminated.
Change all settings at the
U.I. for Infinity/Evolution systems or at the furnace control for Non-Infinity/Evolution
systems to see if the limit switch tripping issue is eliminated-Remember to save your changes when exiting
the U.I!
For other non-variable speed
90% units with PSC blowers verify that the correct speed tap is selected.
For all units continue below:
Is it the correct
limit and shield installed?
For Step Modulating Units, refer to the list of limits and shield at the
end of this checklist. You can also refer to EPIC for the correct limit and
shield combination for the model you furnace have.
Is the limit
shield touching the side of the primary heat exchanger?
Slightly re-bend the shield to make sure it does not touch the primary
HX. Do not over-bend the shield
Make sure the tab that mounts the shield to the cell panel is not bent
more than 90 degrees.
Note
how one side of the limit shield is touching the primary heat exchanger. This
will cause the limit switch to trip in Low Heat (58MVB/355AAV) and Medium Heat
(58MVC/355CAV)
While the limit shield is removed from the cell panel; check to see if
the Rear Air Baffle is installed across the top rear of the condensing heat
exchanger. You may also be able view this baffle by through the open area of
the N coil or removing the blower and looking up between the secondary heat
exchanger cells.
The baffle is a 322052-301 through 309 for Step Modulating condensing
furnaces. Refer to the table at the end of this checklist for the correct air
baffle. For other 90% models, refer to
EPIC.
Return air
connections
Left side of furnace (motor side) Right side of furnace Bottom
Combination: Both sides Right
Side/Bottom Left side/Bottom
Actual CFM in:
High heat________ Cooling__________
Note: A duct
traverse is required to get the actual CFM
Actual Esp in:
Low heat_________ Medium heat_________
High heat________ Cooling__________
Actual Blower Motor
RPM in:
Low heat_________ Medium heat_________
High heat________ Cooling__________
The Blower Motor
RPM can be obtained from the User Interface
Is this a factory
supplied cased or uncased coil?
Supply the dimensions
of the coil or casing in the drawing at the end of this checklist.
N-Coil
Installation:
Is this an uncased
N coil?
How high above the furnace is the coil
installed?
Is the opening in the mounting pan or
shelf as large as the coil opening?
Is this a cased N
coil?
Check the intake
air box underneath the burner box. Does the intake air box have both combustion
air disks installed? Most furnaces and venting sizes require both combustion
air disks installed. The exception would be the 120 and 140 size furnaces using
standard 3 inch elbows and high altitude installations.
Refer to the
venting table including the notes at the bottom of the page.
Clean the trap and
collector box assembly. Water build up can cause the pressure switch to trip,
which will cause the inducer to ramp up to re-close the pressure switch. On
modulating furnaces, this can energize the high stage of the gas valve and
cause high gas flow while the furnace is in medium heat.
Step Modulating Limit,
Shield and Rear Air Baffle Dimensions:
Model
|
Limit
|
Shield
|
Rear Air Baffle
|
Baffle Dimensions
|
58MVC060-14
|
HH12ZB200
|
320711-303
|
None
|
None
|
58MVC080-14
|
HH12ZB180
|
320711-302
|
322052-302
|
11.9” x 4”
|
58MVC080-20
|
HH12ZB180
|
320711-302
|
322052-302
|
11.9” x 4”
|
58MVC100-20
|
HH12ZB180
|
320711-302
|
322052-303
|
14.9” x 5”
|
58MVC120-20
|
HH12ZB170
|
320711-302
|
322052-309
|
14.9” x 5”
|
Model
|
Limit
|
Shield
|
Rear Air Baffle
|
Baffle Dimensions
|
355CAV042060
|
HH12ZB200
|
320711-303
|
None
|
None
|
355CAV042080
|
HH12ZB180
|
320711-302
|
322052-302
|
11.9” x 4”
|
355CAV060080
|
HH12ZB180
|
320711-302
|
322052-302
|
11.9” x 4”
|
355CAV060100
|
HH12ZB180
|
320711-302
|
322052-303
|
14.9” x 5”
|
355CAV060120
|
HH12ZB170
|
320711-302
|
322052-309
|
14.9” x 5”
|
Model
|
Limit
|
Shield
|
Rear Air Baffle
|
Baffle Dimensions
|
58MVB040-14
|
HH12ZB200
|
320711-302
|
None
|
None
|
58MVB060-14
|
HH12ZB200
|
320711-303
|
None
|
None
|
58MVB080-14
|
HH12ZB180
|
320711-302
|
322052-302
|
11.9” x 4”
|
58MVB080-20
|
HH12ZB180
|
320711-302
|
322052-302
|
11.9” x 4”
|
58MVB100-20
|
HH12ZB180
|
320711-302
|
322052-303
|
14.9” x 5”
|
58MVB120-20
|
HH12ZB170
|
320711-302
|
322052-309
|
14.9” x 5”
|
Model
|
Limit
|
Shield
|
Rear Air Baffle
|
Baffle Dimensions
|
355AAV042040
|
HH12ZB200
|
320711-302
|
None
|
None
|
355AAV042060
|
HH12ZB200
|
320711-303
|
None
|
None
|
355AAV042080
|
HH12ZB180
|
320711-302
|
322052-302
|
11.9” x 4”
|
355AAV060080
|
HH12ZB180
|
320711-302
|
322052-302
|
11.9” x 4”
|
355AAV060100
|
HH12ZB180
|
320711-302
|
322052-303
|
14.9” x 5”
|
355AAV060120
|
HH12ZB170
|
320711-302
|
322052-309
|
14.9” x 5”
|
320711-302
No Hole in Shield
|
|
320711-303
1” Hole in Shield
|
See location of Rear Air Baffle below and on next page:
