32.1 Main pressure switch (LPS) open

What the control is telling you

The main (collector box) pressure switch did not close or opened during operation.

Applies to: Carrier 59SC6A

Likely causes

• Blocked vent or combustion air pipe
• Water trapped in vent pipe
• Plugged or unprimed condensate trap / blocked drain
• Kinked, cracked or water-filled pressure tube
• Weak or failed inducer motor
• Failed pressure switch
• Low gas pressure switch (LGPS) open, if that accessory is used

Test and repair steps

1. Warning: Turn off and lock out 115-V power before working on the inducer or switch wiring.
2. Inspect vent and combustion-air terminations and piping for blockage, sags, broken fittings or trapped water; vertical offsets should use 45-degree elbows, as water in the vent causes nuisance pressure switch trips.
3. Check the condensate trap is primed pour one quart (liter) of water through the upper and then middle collector box drain ports; it must overflow the trap to the drain.
4. Flush the collector box and drain with the pressure switch tube raised above the collector box opening, flush through the top and middle ports until the trap discharge runs clean; clean the relief port with a small wire.
5. Remove and rinse the condensate trap in warm water and flush drain lines; install a new trap gasket if the trap is removed.
6. Inspect the pressure switch tube for kinks, cracks or water.
7. Ct component test (control in idL, no W/Y/G call): PUr inducer on for the whole test; HSI on after 10 s for 15 s; Fn blower on 10 s; End inducer runs 10 more s.
8. Switch check with inducer leads disconnected and a heat call, the igniter must NOT glow and a pressure switch code should appear; if the igniter glows, shut the furnace down immediately.
9. If draft is good and the switch still won't close, replace it.

Settings for these units

• Filter sizes by casing width and filter cabinet · 59SC6A
• Minimum clearances to combustibles · 59SC6A