LAARS U.H.E. - Service Manual - Manual (Page 27)

U.H.E Service Manual Page 27
Reset button
Does blower
energize?
N
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 to 5 minutes waiting for the contacts to close.
If the contacts remain open, the blower will stop and the PURGE LED will flash for hot surface ignition models.
Check PURGE LED status.
Y
Refer to
“Check Collector Pressure”
(see next page)
Check blower for proper
operation (see page 25)
Is blower OK?
N
On within 5 minutes? Pressure switch is OK.
Y
Y
Safety Circuit Trace
LED Status
Only power LED is on, or
Purge LED flashing.
Exhaust Pressure Switch Testing and Replacement
N
WARNING
120 volt potential exposure. Use caution
making voltage checks to avoid personal injury.
Flashing after 5 minutes?
Error code 29 again?
Call for technical
support.
Correct blower problem
(see page 25)
N
Y
Note: HOT SURFACE IGNITION MODELS
ONLY - The blocked vent pressure switch
must be used with the revised ignition control,
identified with a yellow label.
Heater side
harness
Control side
harness
27
Y
Is there continuity
Through GREY
wire leads of heater side
safety circuit harness?
(see photo below)
N
Y
Is there continuity
through RED
wire leads of heater side
safety circuit harness?
(see photo below)
N
Safety Circuit OK,
(see page 36)
Replace exhaust
pressure switch (see
page 29)
Replace vent safety
switch.
(see page 37)
Call technical
support.
Y
N
Depress reset
button on vent
safety switch. Is
there continuity
across high limit
switch?
(see photo below)
Check PURGE LED status
on ignition module,
Flashing after 45 seconds?
Does heater
function?
Verify proper
switch operation.
(see page 36)
N
Y
Y
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.