E4 Pressure switch cycle lockout

What the control is telling you

The pressure switch has opened and closed repeatedly during the cycle and the control has locked the furnace out. Troubleshoot it the same way as E2/E3.

Applies to: Midea BGH96M 96% AFUE two-stage gas furnaces (060B3A, 080B3A, 080C4A, 100C5A, 100D5A, 120D5A)

Likely causes

• Partially blocked vent/exhaust causing marginal pressure
• Pressure hose loose, cracked or holding water/debris
• Weak inducer
• Pressure switch near its set point / faulty
• Intermittent wiring

Test and repair steps

1. Warning: Kill 115 V power and discharge static to bare furnace metal before touching the control or wiring.
2. Check the wiring to the pressure switches for loose or wrong connections; correct per the wiring diagram.
3. Inspect the exhaust/vent pipe for blockage and clear it.
4. Inspect the pressure hose make sure it is firmly connected and not kinked, cracked or plugged; clear or replace it.
5. Pull the hose and measure the pressure the inducer produces with a manometer: low-fire switch set point is 0.55 in. WC, high-fire switch set point is 1.1 in. WC.
6. If pressure is below the set point, check the inducer and replace it if it is weak or not running.
7. If pressure is correct, check that the switch closes (about 0 VAC across its terminals while running); if it does not close, replace the pressure switch.
8. If the switch closes and the code remains, replace the control board.
9. Reset the lockout interrupt 115 V power for 1-20 seconds, or remove the thermostat call for 1-20 seconds (control also self-resets after 1 hour).