If the air filter is dirty, excess pressure will build up across the filter, triggering the normally closed air pressure switch (PF) to open.
Troubleshooting
| Possible Cause | Component to Check | Recommended Action |
| Dirty air filter | Air filter. Open the middle-front panel to access the filters. | Replace air filter. |
| Switch tubing | Tubing leading to switch | Verify that tubing is clear and that it is not kinked |
| Incorrect wiring | Alarm wiring | Correct wiring. Refer to the Dirty Air Filter Alarm Wiring diagram below. |
| Incorrect air pressure switch setting | Arrow on the dial should be pointing at 250 | Correct setting to 250. |
| Faulty air pressure switch | Air pressure switch | If the switch is open while the filter is clean and setting is correct, replace the switch |
Dirty Air Filter Alarm Wiring
