Pressure Switch Testing And Replacement - Bradford White M1TW40S Series Service Manual

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
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,
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 29)
Page 18
18
1
Check tubing and pressure
N
tap on switch for blockage.
Y
Check tubing and
N pressure tap on N
switch for blockage.
Is there blockage?
TTW SERVICE PROCEDURE III
Pressure Switch Testing and
115 volt potential exposure. Use caution
making voltage checks to avoid personal injury.
Pressure switch
Slide pressure switch in direction
wire leads
of arrow while tilting slightly away
from blower housing.
N
Is there blockage?
Y
Clear blockage
Y
Is vent system length
Is vent
N within vent table
system
specifications
blocked
listed on pages 7 & 8
Reconfigure vent
system to be
compliant with
vent tables.
Replacement
WARNING
2
Pressure Switch
Replace switch
(see page 19)
See blower testing
Y
(page 20)
Is blower OK?
N
Correct blower
problem.
Y
N
Page 18