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Model MSX Make-Up Air
Proper supply power at
main disconnect
Check main voltage
(See Blower Start-Up Step #1)
Main Disconnect (DS1) Off
(Turn Main Disconnect DS1 On)
Primary fuses blown
(Replace fuses)
24 VAC between
terminals R and X?
Main Transformer (TR1) Defective
(Replace transformer)
24 VAC between
terminals G and X?
Supply Switch (S2) Off
(Turn Supply Switch (S2) On)
Fire System Contact (FSC) tripped/not installed
(Correct/Replace)
No
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Blower Does Not Operate
Broken fan Bbelt
(Replace. Reference Maintenance section)
Defective motor or capacitor
(Repair/Replace)
Blown motor fuse
(Replace)
One or more legs of 3 phase is out
(Restore missing legs)
24 VAC across A2 and A1 on
supply contactor (ST1)
24 VAC across
terminals 4 and X?
24 VAC across
terminals 3 and X?
Supply Fan Overload (ST1 OL) tripped
(Reset and check motor amps. Reference Blower Start-Up #4)
Optional Exhaust Fan Interlocks (ST2-ST5) open
(Correct/Replace)
(Optional) Damper Limit Switch (DL1) holding
(Wait for actuator to open fully or adjust limit switch)
(Optional) Damper Limit Switch jumper missing
(Install jumper. Reference the unit’s ladder diagram for terminals)
Fan Relay (RF) is not energized
(Check for loose connection) (Repair or replace relay)
(Optional) Freeze Protection (RT4) Tripped
(Reset)
Troubleshooting
At this time the supply contactor (ST1) should pull in,
passing power to the supply motor
and the blower should start.