1. Blocked venting
2. Blocked air inlet
3. Disconnected, damaged or blocked tubing.
4. Incorrect air switch setting.
5. Blown fuse
1. Check for blockage of the exhaust vent.
2. Check for blockage of the air inlet.
3. Inspect the clear vinyl tubing connecting the air switch + and – ports to the air metering elbow. Condensation or other foreign matter may be obstructing the tubing, preventing the switch from sensing differential pressure caused by air flow through the metering elbow.
4. Contact NTI technical support.
5. Check Fuse "A".
