Have HVAC Questions? Ask an HVAC Expert for Answers
on this unit there are up to 3 switches in series with the pressure switch.
Have they checked the inducer limit?
This is commonly a venting issue...too small pipe or too many 90's etc.
The air switch should bench test open...the limit and inducer limit in the same series should test closed.
The only open switch is the pressure switch...once the draft motor starts te air flow created by the exhaust sucks air through the tube and closes the switch.
This allows ower to go on through to the the next 2 switches...one is a high liit normally closed...this opens if interior of furnace gets to warm (like plugged filter, too slow blower)..the next switch is also heat activated but is if the inducer housing gets too hot.
These last 2 switches can open and close on their own accordiing to temps,
The only open switch should be the air switch and it should close on start up.