Service Manual

TTW SERVICE PROCEDURE III
Pressure Switch Testing and
Replacement
Pressure Switch Testing
WARNING
115 volt potential exposure. Use caution
making voltage checks to avoid personal injury.
Step 1. Position power switch on gas control
to the “OFF” position.
Step 2. Remove the three screws (Phillips screw driver) from control access cover on blower assembly and
remove cover (see photo 1).
Step 3. Carefully remove pressure switch from blower housing (see photo 2)
2
Use a multi-meter set to the
ohms setting. With blower off,
check across pressure
switch terminals.
Are switch contacts open?
(no electrical continuity)
Check tubing and pressure
tap on switch for blockage.
Is there blockage?
Replace switch
(see page 19)
Position gas valve power
switch to the “ON” position
and adjust thermostat
to call for heat,
this will start the blower.
Check with multi-meter, do
pressure switch contacts
close with blower running?
1
With steps 1,2 & 3
complete,
disconnect wire leads from
pressure switch.
Y
N
Y
N
Switch contacts are OK.
See safety circuit trace
(page 29)
Is vent
system
blocked
N
See blower testing
(page 20)
Is blower OK?
Clear blockage
Y
N
Y
N
Correct blower
problem.
Pressure Switch
Slide pressure switch in direction
of arrow while tilting slightly away
from blower housing.
Is vent system length
within vent table
specifications
listed on pages 7 & 8
Y
Reconfigure vent
system to be
compliant with
vent tables.
N
Y
Pressure switch
wire leads
Page 18
Check tubing and
pressure tap on
switch for blockage.
Is there blockage?
N
Y
pg18.pdf 1pg18.pdf 1 4/7/06 11:25:02 AM4/7/06 11:25:02 AM
Page 18