DGAA070BDTB Pressure switch failure.

[mjcp]

This furnace is flashing 3 times indicating a pressure switch failure.
the problem is intermittant yet most of the time. eg: three cycles in a row furnace runs fine, then 4th cycle fails, and 8 attempts after fail. Furnace is about 4 years old.

VOM shows 28v +/- on the switch when it works, <1 volt when it does not work.
Switch can be actuated reliably and consistantly when tested off unit (Continuity test while applying slight positive air flow).

The combustion motor is coming on and can be heard operating. two hoses enter the housing from the pressure switch, the lower air hose can be easily blown into with no apparent resistance, the upper hose is much harder to blow through. A small wire (guitar string) passes easily through both connectors ( no obstruction). Both hoses were trimmed to assure a good snug fit.

I am suspecting from what I have read here either the motor is not running at full speed, or there is blockage in the exhaust. (The vent from the roof down was inspected and looks fine but thats no gaurantee).

How would I get to the motor on this unit to check it or replace it? it appears the furnace was built around this with screws that I cannot reach. Am I missing something here? It doesn't look like it can be dissassembled.

Any help is appreciated.

Mike

[Robert]

Hi,

You should have 24 to 28VAC at one side of pressure switch to ground at all times. When it fails, IF you do not have the 24vac at one side, then need to find break in low voltage circuit to the switch.



Thanks,
Robert

[mjcp]

I do have voltage to one side (the rear leg), and the other leg only has voltage when the switch actuates.
The problem seems to be intermittent low pressure to the switch - which could be the motor or blockage?? , we don't seem to have blockage so I'm trying to troubleshoot the motor, but I don't see how to access the motor. It is inside the exhaust pipe, and there is no apparant method to dissasemble without a SAWSALL. Just curious how to get to the motor to replace it?

[Robert]

Hi,

You remove the whole section and you can see motor from open end. You cannot order just the motor, it is all one piece, motor and pipe housing.



Thanks,
Robert