PDX SERVICE PROCEDURE III

Pressure Switch Testing and

Replacement

Inlet Pressure Switch
Testing WARNING
120 volt potential exposure. Use caution
making voltage checks to avoid personal injury.

Step 1. Position power switch on gas control

to the “OFF” posit ion.

Step 2. Remove the three screws (Phillips screw driver) from control access cover on blower assembly and

remove cover (see photo 7).

Step 3. Remove wires from inlet pre ssure switch.

Use a multi-meter set to the
ohms setting. With b lower off,
check across pressure
switch terminals.
Are switch contacts clo sed?
Check tubing and p ressure
tap on switch for blockage.
Is there blockage?
Replace switch
(see page 20)
Position gas valve pow er
switch to the “ON” position
and adjust thermostat
to call for heat,
this will start the blo wer.
Checkwith multi-meter, do
pressure switch cont acts
remainclosed with blower
running withthe switch in
the vertical postit ion?
With steps 1,2 & 3
complete.
Y
N
Y
N
Switch contacts areOK.
See exhaust pressure
switch testing(page 17)
Is vent
system
blocked
NSee blower testing
(page 21)
Is blower OK?
Clear blockage
Y
N
Y
N
Correct blower
problem.
Is vent system length
within vent table
specifications
listed on page7
Y
Reconfigure vent
system tobe
compliant with
vent tables.
N
Y
Page 19
Check tubing and
pressure tap on
switch for blockage.
Is there blockage?
N
Y
PDX Series
7
Exhaust
pressure switch
Inlet pressure
switch
Inlet pressure
switch wire
leads (found
inside cover)
19