Pressure Switch Questions

[Gynotai]

Hi.

I have a Coleman DGAA070BDTA, and I'm getting three flashes on the Control Board telling me it's not seeing the Combustion Air Switch close.

Being an Electronic Tech by trade, I took this switch off and grabbed my DVM. It appeared to be stuck open because only after I applied pressure, then suction VIA blowing into it (which I just read I shouldn't have done), I started seeing a reading on the DVM; around 200 ohms. This leads me to my questions:

1) Are the presure switches delicate, as in only a minute amount of pressure would make a working one close? Did I destroy this Presure Switch by blowing into it?

2) What resistive reading should I expect to see from a working switch?

3) The fan in the flue works, but it doesn't seem like it would create enough pressure to close the switch, which I'm assuming is causing it to fail.

Thank you for all your help!

Thom

[Robert]

Don't take a lot to mess them up. Blowing in them creates moisture which is bad. Resistance is low, would have to look that furnace up to know exactly how low. I never waste time ohming them.

Check water column pressure of tubes to know if motor is producing what is needed to close switch. It should open automatically at end of cycle each time.


Switch will show needed w.c. pressure on front/top of it.


Thanks,
Robert

[Gynotai]

Hi Robert.

Thank you for your quick reply.

I guess the best way to see if the switch is working is to install it, and connect a meter to it. When I power the Furnace on, if it's working properly, I should get 24 VAC through it, right?


I also may have to face the fact that it's a very delicate switch, and in my attempt to fix it, I made it worse.

Thanks again!

Thom

[Robert]

Hi Thom,

Sometimes you can get away with blowing in them, just don't do it repeatedly. Basically most MH hvac parts are delicate in a sense.


Yes, IF it closes, 24vac will go through it.


Thanks,
Robert