Troubleshooting
Electric Heater Does Not Operate (optional)
Supply fan must be on for heater to operate
24 VAC between
terminals W1 and X?
Yes
24 VAC between
terminals 22 and 21?
Yes
24 VAC between
terminal A2 on heat relay (RH)
and X?
Yes
24 VAC between
terminals T1 and 21?
Yes
24 VAC between
terminals I and 21?
Yes
No
No
No
No
No
Heat Switch (S4) Off
(Turn Heat Switch (S4) On)
Heat Switch not wired
(Wire Heat Switch (S4))
Main Transformer (TR2) defective
(Replace transformer)
(Optional) Inlet Air Sensor (TS4) holding (Adjust (TS4) setting. Reference Blower
Heat Relay (RH) is not energized
(Check for loose connections). (Repair or replace Heat Relay (RH))
Pressure Differential Switch (PDS) open
(Check on cause of control loss)
Automatic and/or Manual Reset Cutouts (A and M) tripped (Reset/Replace Automatic and/or Manual Reset Cutouts (A and M))
(Check on cause of control loss)
At this time the heater should be energized. (The heating elements will not be on if the leaving air temperature is above its set point on the Remote Adjuster (RA))
30 | Model MSX | ® |
