Bradford White PDX-75S-70FB-3X - Manual (Page 25)

PDX SERVICE PROCEDURE V
Blower Temperature Switch Testing
and Replacement
Blower Temperature Switch
Testing.
WARNING
120 volt potential exposure. Use caution
to avoid personal injury.
15
Disconnect wire leads to
switch. Using a multi-meter
set to the ohms setting, is
there continuity between the
switch terminals?
Switch OK
Cool switch to
below 125°F
N
Y
Switch Setting
Opens on rise @ approximately 155°F
Auto resets on fall @ approximately 128°F
Step 1. Position power switch on gas control
to the “OFF” position.
Step 2. Remove tubing from inlet pressure tap.
Step 3. Remove the three screws (Phillips screw driver) from
control access cover on blower and remove cover (see
photo 15).
Step 4. Locate blower temperature switch (see photo 16)
Reconnect wire leads and
observe heater operation. Do
exhaust gas temperatures rise
to or above 175°F?
Replace switch
(see page 24)
Y
N
Do switch contacts
open?
Do switch contacts
open?
N
Y
Replace switch
(see page 23)
N
Y
Exhaust
temperature is too
hot.
Common causes for
high exhaust temperature
1. Vent length is below minimum allowable.
2. Vent diameter not to specification.
3. Restricted dilution air inlet.
4. Missing or deteriorated flue baffle.
5. Gas pressure is out of specification.
6. Excessively high ambient temperatures.
Blower temperature
switch location
16
Air mixing inlet
Page 24
DX Series
Common causes for
high exhaust temperature
1. Vent length is below minimum allowable.
2. Vent diameter not to specification.
3. Restricted dilution air inlet.
4. Missing or deteriorated flue baffle.
5. Gas pressure is out of specification.
6. Excessively high ambient temperatures.
25