Service Manual

83
Service Procedure VI
Blocked Vent Pressure Switch Testing and Replacement
Sequence of Operation: The blocked vent pressure switch monitors the pressure in the exhaust tube. The switch
contacts are normally closed and will not open unless there is a blockage in the exhaust venting or terminal (snow, ice,
debris). If the blocked vent pressure switch contacts open after the thermostat initiates the blower, the blower will remain
on for up to 5 minutes waiting for the contacts to close. If the contacts remain open, the blower will stop, and error code
29 will display.
WARNING
120 volt potential exposure. Use caution
making voltage checks to avoid personal injury.
WARNING
Make sure exhaust collector compartment is not
overheating (350°F) before resetting vent safety switch. If
there is evidence the collector compartment is overheating,
call Technical Support.
LED Status
Only power LED is on, or Purge LED flashing.
Error Code 29 or 26
Does the blower
energize?
Is there
continuity
through gray
wire leads of
heater side
safety circuit
harness? (see
image below).
Is there
continuity
through red wire
leads of heater
side safety
circuit harness?
(see image
below).
Safety circuit
O.K. (see
Blower
Testing and
Replacement,
pg 82).
Check Purge
LED status on
ignition module.
Is it flashing after
45 seconds?
Replace
exhaust
pressure
switch (see
Exhaust
Pressure
Switch
Replacement
Procedure)
Depress reset
button on vent
safety switch.
Is there
continuity
across high
limit switch?
(see image
below).
Replace vent
safety switch (see
Vent Safety
Switch
Replacement
Procedure, pg
93)
Check control display.
On within 5 minutes?
Flashing after 5 minutes?
Error code 29 again?
Check blower for proper
operation; Is blower
O.K.?
Refer to Check Collector Pressure (see next page).
Pressure switch is O.K.
Call Technical
Support.
Correct blower problem
(see Blower Testing and
Replacement, pg 82).
Call
Technical
Support.
Does the heater function?
Verify proper switch operation. (see Vent Safety
Switch Testing and Replacement, pg 92).
Y
Y
Y
Y
Y
Y
Y
Y
N
N
N
N
N
N
N
N
Y
Safety Circuit Trace
Reset Button
83