UniMac Commercial Dryer Error Code AF-1: Airflow Switch Closed Early
AF-1 means the airflow switch on a UniMac 120 or 170 lb dryer was already closed when the cycle started, before the blower moved any air. Turn the dryer off, let it cool, and clean the lint screen. The switch itself should not be touched, so call us.
High: the dryer will not run its burner until the airflow switch circuit is corrected.
What does UniMac error code AF-1 mean?
The airflow switch is a safety proof. Before the burner is allowed to fire, the control wants to see that the blower is moving air, which should close the switch. At the very start of a cycle, with the blower not yet running, that switch should still be open. AF-1 appears when the control finds it already closed at that moment. A switch that reads closed with no air cannot be trusted to prove anything later, so the control holds the cycle instead of lighting the burner. The usual reasons are contacts that have welded or stuck shut, a shorted wire or damaged connector on the switch circuit, a blocked sensing tube or stuck vane that holds the switch closed, or a control input that reads the circuit as closed when it is not. This is the opposite problem from AF-2, where the switch fails to close once air should be moving.
Affected models and control systems
This applies to UniMac tumble dryers of 120 and 170 lb capacity with the On Premise Micro control, such as the UA120L, in the TMB1268C troubleshooting family.
Code numbers and their meaning can change between control generations. We match the full model and control before acting on a code.
What you may notice
- AF-1 on the display at the start of a cycle
- Cycle that will not begin or hold
- No burner ignition after the start key is pressed
Possible causes
Listed in UniMac's documentation
- Airflow switch contacts that are welded or stuck closed
- A shorted wire or damaged connector on the switch circuit
- A blocked sensing tube or stuck vane holding the switch shut
- A control input that reads the switch as closed
Other likely causes — what usually sits behind error code AF-1 on this control. A technician confirms which one it is before any part is replaced.
- Lint packed around the vane so it cannot drop back to its open position
- Moisture in the switch connector bridging the two terminals
- A wire rubbed through against the cabinet, grounding the switch circuit
Safe checks before calling for service
- Turn the dryer off so it can cool.
- Clean the lint screen and the area around the door opening.
- If you ever smell gas, leave the building and phone the gas utility from outdoors.
- Do not touch the switch or open panels.
- Note whether AF-1 shows at every start or only some, and call us.
How a technician diagnoses error code AF-1
- Confirm the code appears at start-up with the blower stopped.
- With power off and locked out, inspect the airflow switch, vane and sensing tube for lint or binding.
- Check the switch contacts with a meter in the no-airflow state; they should read open.
- Inspect the switch wiring and connector for a short or damp terminals.
- If the switch tests open but the code stays, check the control input.
- Replace the switch or wiring only after the test, then run a full heat cycle.
- The switch proves airflow before gas is lit, so a stuck one is a gas-safety matter that must not be bypassed.
- Testing the circuit means working inside the cabinet near live control wiring.
- Telling a stuck switch from a bad control input needs a meter, not guesswork.
How error code AF-1 differs from similar codes
AF-1 and AF-2 are opposites: AF-1 is a switch closed too early, while AF-2 is a switch that never closes once air should be moving.
Technical reference
- Document
- Tumble Dryers 120/170 lb Troubleshooting TMB1268C, Part No. 70399901R2, Dec 2016 (pp.53, 65)
- Maker documentation
- UniMac owner support
- Edition
- Part No. 70399901R2, December 2016; models through serial no. 0907000048
- Models / control
- Tumble dryers 120/170 lb (TMB1268C family) micro control
- Section
- Hybrid Timer Control Troubleshooting - 31. Error Codes, printed p. 53 (PDF p. 55); On Premise Micro Control (RM) Troubleshooting - 36. Error Codes, printed p. 65 (PDF p. 67)
- Checked
- October 2026
We use the maker's document to read the code and do not reproduce it. Always confirm the complete model and control before applying these steps.
Can I keep drying with AF-1 showing?
No. The control will not run the burner while it cannot trust the airflow switch.
Will cleaning the lint screen clear it?
It is worth doing, but AF-1 points to a switch that is stuck shut, not to a lack of air.
Is it the same as AF flashing?
No. A flashing AF means the switch opened and closed 5 or more times in one cycle. AF-1 is about the state at the start.
Need help with UniMac error code AF-1?
A technician confirms the cause on site and gives you the price in writing before any work starts.