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Model MSX Make-Up Air
Electric Heater Does Not Operate (optional)
Supply fan must be on for heater to operate
Troubleshooting
24 VAC between
terminals W1 and X?
Heat Switch (S4) Off
(Turn Heat Switch (S4) On)
Heat Switch not wired
(Wire Heat Switch (S4))
24 VAC between
terminals 22 and 21?
Main Transformer (TR2) defective
(Replace transformer)
24 VAC between
terminals I and 21?
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)
24 VAC between
terminals T1 and 21?
Heat Relay (RH) is not energized
(Check for loose connections). (Repair or replace Heat Relay (RH))
24 VAC between
terminal A2 on heat relay (RH)
and X?
(Optional) Inlet Air Sensor (TS4) holding
(Adjust (TS4) setting. Reference Blower Start-Up Step #6)
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
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))