LAARS NeoTherm NTV (Sizes 399-850 MBTU/h) - Service Manual - Manual (Page 49)

39
Service Manual - NeoTherm 500
1. The switch is located behind the front panel. Dis-
connect the two leads, and connect a Volt-Ohmme-
ter set to check for continuity (reading Ohms).
2. Insert a hose “T” in the clear plastic hose that runs
to the positive pressure port (closest to the electrical
connections). Attach a length of hose to the branch
of the “T.”
3. Blow on the end of the hose.
With pressure –
You should see continuity (low Ohms - switch
closed)
Without pressure –
You should not see continuity (high Ohms – switch
open)
4. Disconnect the “T.” Attach a manometer to the
negative port on the blower. When the fan starts,
you should see a vacuum of about ½” w.c.
Removing and Replacing the Air Pressure Switch
Fig. B21-1 - Air pressure switch (typical)
The air pressure switch acts as a “blower proving switch”
to ensure that the blower is running before the unit will
fire.
Tools and equipment required
• Small Phillips-head screwdriver (#1) or 5/16” socket
• Small standard pliers
• Electrical tape
B20
Test Procedure for Air Pressure Switch
B21