Run capacitor
Common no-start and weak-compressor failure point. Match the microfarad and voltage rating.
Carrier 22 Error Code — What It Means
Carrier fault code 22 indicates a limit device lockout on a single-stage furnace — sometimes described in older Carrier documentation as an LSOM (Limit Switch Open Multiple times) stall. The control board has detected that the high-limit switch opened three or more times during a single heating cycle. After repeated limit trips, the board locks out and displays code 22 to signal that the system cannot safely continue heating until the root cause is resolved.
Common Causes
- Restricted airflow — A clogged filter, blocked return grille, or closed supply registers prevents adequate airflow across the heat exchanger, causing it to overheat and repeatedly open the limit.
- Oversized furnace / short cycling — If the furnace is significantly oversized for the space, short run cycles can cause rapid heat buildup with insufficient blower time to dissipate it.
- Weak or failed blower motor — A motor running below rated RPM due to a bad capacitor or worn bearings moves less air, leading to heat exchanger overtemperature.
- Faulty or stuck high-limit switch — A limit switch that opens at too low a temperature (due to calibration drift or physical damage) will trigger code 22 even with proper airflow.
Step-by-Step Fix
- Replace the air filter — Confirm the filter is the correct size and MERV rating. A filter that is too restrictive is as problematic as a dirty one.
- Check all supply and return registers — Open any registers that are closed. Ensure furniture, rugs, and debris are not blocking return air grilles.
- Inspect the blower motor and capacitor — Power off the furnace. Spin the blower wheel by hand to confirm it rotates freely. Test the run capacitor with a capacitor meter; replace if the reading is more than 10% below the rated µF value.
- Test the high-limit switch — With power off, use a multimeter on continuity mode across the limit switch terminals. It should show continuity (closed) at room temperature. If it is open at room temperature, replace the switch.
- Reset the lockout — Cut 120V power to the furnace for 30 seconds to clear the code 22 lockout. Restore power and run a full heat cycle while monitoring for limit trips.
Parts Often Needed
| Part | Notes |
|---|---|
| Air filter | Most common fix; replace first |
| Blower run capacitor | Match µF and voltage exactly to OEM spec |
| High-limit switch | Verify OEM part number; temperature rating varies by model |
| Control board | Replace only if board relay is confirmed faulty |
Technician Tips
Carrier uses different diagnostic systems across furnaces, heat pumps, chillers, mini-splits, VRF equipment, rooftop units, and communicating controls. Confirm the full model number and whether the fault came from the indoor board, outdoor board, thermostat, or equipment controller before matching it to a repair path.
Start with power, wiring, airflow or water-flow, sensor, condensate, and safety-circuit checks before ordering control boards. If the same code returns after one reset and the basic cause is not obvious, test the named circuit instead of repeatedly cycling the equipment.
Common replacement parts for Carrier systems:
- Carrier flame sensor (part #HH18ZA641)
- Limit switch kit (part #HH18HA600)
- Pressure switch (part #HH18HA719)
Need Replacement Parts?
Before ordering, match the HVAC part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
When to Call a Pro
If the limit switch resets but opens again within one heating cycle and airflow is verified good, a cracked heat exchanger may be allowing combustion gases to recirculate. This is a carbon monoxide hazard — do not operate the furnace until a licensed technician inspects the heat exchanger.