Bradford White TTW 75 SERIES Service Manual page 17

Pressure Switch Testing
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)
With steps 1,2 & 3
complete,
disconnect wire leads from
pressure switch.
Use a multi-meter set to the
ohms setting. With blower off,
check across pressure N
switch terminals.
Are switch contacts open?
(no electrical continuity)
Y
Position gas valve power
switch to the "ON" position
and adjust thermostat
to call for heat,
N
this will start the blower.
Check with multi-meter, do
pressure switch contacts
close with blower running?
Y
Switch contacts are OK.
See safety circuit trace
(page 28)
making voltage checks to avoid personal injury.
1
Pressure switch
wire leads
Check tubing and pressure
tap on switch for blockage.
Is there blockage?
Clear blockage
Y
Check tubing and
Is vent
pressure tap on
N
system
switch for blockage.
blocked
Is there blockage?
TTW SERVICE PROCEDURE III
Pressure Switch Testing and
Replacement
WARNING
120 volt potential exposure. Use caution
Slide pressure switch in direction
of arrow while tilting slightly away
from blower housing.
N Replace switch
(see page 18)
Y
Y
Is vent system length
within vent table
N
specifications
listed on page 7
N
Reconfigure vent
system to be
compliant with
vent tables.
2
Pressure Switch
Y
See blower testing
Y
(page 19)
Is blower OK?
N
Correct blower
problem.
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