4YCC4 - Flashing Code 3

Article ID: 426
Last updated: 18 Sep, 2023

Trane Package Unit: 4YCC4

Re: Flashing Code 3

Code 3 = Pressure Switch Fault

A Code 3 will be generated in either of the following conditions:

  • The pressure switch failed to close with the inducer motor energized.
  • The pressure switch failed to re-open with the inducer motor de-energized.

Qty Possible Causes:
Bad Pressure Switch
3 Bad Inducer Motor
Loose Pressure Switch Hose 
Clogged Pressure Port
Bad Ignition Control Board


1. Check Controller

2. Check Inducer Motor

  • With "W' energized, check for 230VAC power between the IGN "Inducer Load" 21A (YL) and CC2 2C (BK).
    • No Power = Pressure Switch Stuck Closed or Bad Control Board → Step 3. Check Pressure Switch
    • Power + No Fan = Bad Inducer Motor or Capacitor

3. Check Pressure Switch 

  • Ensure that the pressure switch hose is attached at the inducer pressure port and the pressure switch.
  • Contacts
  • With "W" energized:
  • Check for 24VAC from each pressure switch terminal to Gnd.
    • Power on Both Sides = Switch Closed 
    • Power on One Side Only = Switch Open
      • Switch Open + No Power to Inducer = Bad Control Board
      • Inducer Off + Switch Closed = Bad Pressure Switch (Stuck Closed)
        • Remove one wire from the pressure switch and see if motor starts.
  • Pressure
  • With the inducer running, use a pressure gauge to check the inducer negative pressure.
    • Pressure Above Switch Rating + Open Switch = Bad Pressure Switch
    • Pressure Below Switch Rating = Clogged Pressure Port or Broken Inducer Fan Wheel (Bad Inducer Motor)

4. ADPS Switch Setting

  • The ADPS switch will sometimes fail to re-open when set for the lowest setting.
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Article ID: 426
Last updated: 18 Sep, 2023
Revision: 8
Views: 13
Comments: 0