Checking the pressure switch on a gas furnace

Measuring ohms on an energized 80% gas furnace

Category:

Education

Tags:

• gas
• furnace
• pressure
• switch

[SiggyMe]

Do you mean by infinity reading a large number or essentially a number close to zero? Thanks doc

[kisssfan]

On this particular meter, infinity would read as an "OL" meaning open line. In other words, the meter is actually sending out a voltage from it's batteries thru this switch and will display that voltage in an "ohm" value if it receives it back. If the circuit fails to close there will be no voltage back to the meter, and it can be thought of as reading infinity because the signal response will never come back to the meter. The signal sent out just continues on and on forever.

[kisssfan]

The pressure switch shown in this video does not have an impeller in it. There is a pressure sensitive diaphragm and contacts that allow 24 volts to pass thru it when the inducer fan is operating. The inducer creates a negative pressure which is transfered to the pressure switch via a tube which in turn closes the diaphragm and contacts. This then allows the sequence of operation to continue. It is a safety switch which proves the proper operation of the inducer fan.

[kisssfan]

No we haven't shorted out a transformer, nor have we blown the 3 amp fuse located in the circuit board. The wire terminals are factory insulated for that reason. If you turn the power off, the inducer fan as well would be turned off and it could not pull the negative pressure required to close the pressure switch. So, ultimately that would be useless. Thanks for your concern.

[rwakie]

Does it matter which wire goes where on a pressure switch? I unhooked mine and I'm not sure which order they need to go in.

[rualatino]

Respond to this video... TWO thumbs up on the use of meter. system did not let me take the thumb down away .

[rualatino]

@kisssfan TWO thumbs up. great explanations of use of the the meter

[50srefugee]

Just fixed my parents' furnace by clearing the pressure port in the combustion chamber blower housing. (By poking a wire into the port until the very hard obstruction cleared.)

Does this mean that the chamber, or the blower housing, is caked with hardened soot? Should I disassemble the blower housing to clean it?

[1990RandomHero]

there is no power throu that switch, since he removed the circuit board leads at the beginning, so he is able to ohm it, the inducer motor created a negative draft which will close a properlly operating pressure switch allowing for an ohm reading. DONT ohm it with those leads connected

[MisterPadrino13]

Arent you suppose to never use your ohmeter on a live circuit ??

[archeryman5000]

The thing to remember is the pressure swith has to start open, then close or the furnace will not heat.

[jennmakela]

i was under the impression that you could not test for resitance or ohms while the power was on or you could fry your meter. Do you have a special multi-meter ?

[Nutintoitbut2doit]

Nice meter