How the Gas Furnace Pressure Switch Works & Testing!

[@acservicetechchannel]

Tool List- www.amazon.com/shop/acservicetech Support- www.patreon.com/acservicetech For those that are looking for the tools used in the videos: (Linked Below) Here is the link to the Fieldpiece SDMN6 Dual Pressure Testing Manometer with Pump-amzn.to/2jyK5Ka Here is a link to the UEI DL389 Multimeter used in the videos- amzn.to/2av8s3q Here is a link for the Supco Magnet Jumpers amzn.to/2gS4h6z Here is the link for the Irwin Wire Stripper/Cutter/Crimper amzn.to/2dGTj2V Other tool links can be found in the video description section. ACSERVICETECH is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.

[@modsavant]

It took me 12 KZbin videos and lots of reading to finally figure out my problem, and your explanation between the 8 and 9 minute mark was the key to putting the pieces together in my head. A simple fix of the air hose plumbing fixed everything and now we have heat again. Thank you!!

[@lancerudy9934]

Very nice job . You very nice job on going over the rating of the switches thank for helping us

[@acservicetechchannel]

Thanks Lance!

[@gilbertopatino2616]

Thank you very much for another excellent video. May God bless you.

[@acservicetechchannel]

May the Lord Bless you too Gilberto Patino! Thanks

[@jermainemyers5596]

I needed this. Thank you.

[@dennispittman4555]

Thanks for educating the masses. Great help in building my prototype

[@acservicetechchannel]

Thanks Dennis Pittman!

[@HsingSun]

Thank you for your video. Did you post the Electric Furnace Pressure Switch works & testing?

[@keithrenison5730]

Great video! So here's a question: my Trane uses a dual port (with +/- connections) that requires a 1.4WC negative draft. I've tested the hose from the secondary exchanger which pulls 1.6 to 1.8 continuously while running. It's connected to the negative (-) side of the pressure switch. The hose from the burner box/gas draws about .10 to .08 negative pressure while running. For some strange reason, the switch will not close when the unit first starts. However the whole thing works perfectly (on/off/run) if I disconnect just the hose from the burner box (the differential is just the atmospheric pressure). If I reconnect the burner box hose while running it keeps running, but won't work when it cycles off and back on. I replaced the sensor, vacuumed all lines, cleared the trap, etc. I also replaced the inducer motor to ensure it wasn't the issue. The HVAC guy says the only thing it could be is a bad secondary exchanger (which is under warranty even though the unit is 14 yrs old). When I replaced the inducer motor I caught a glimpse of the secondary exchanger and it looks really clean. Any ideas? I can only guess that for some reason there's too much pressure in the burner box or not enough in the secondary exchanger (clogs I can't see?) and indeed it needs replaced? Blerg!!!!

[@ilovenythismuchilovenewyor5801]

pay your professionals

[@fourfoldarchives]

I've got a Trane XB90 doing the exact same thing. Manometer results are simliar to yours, plenty of pressure to open/close the switch. Tried new pressure switch, inducer motor, and control board. Did you ever resolve this?

[@capitolrefrigerationheatin7501]

nice presentation!!!!!!!!!

[@acservicetechchannel]

Thanks Capitol!

[@esbigerodeo1]

any idea on when you may do the video on the diffrence of microns and inches of mercury?

[@acservicetechchannel]

Sorry Evan, I do not know as of yet. I will have to work that topic into a video maybe on prepping for epa608. Thanks for reminding me!

[@wangandrew607]

Thanks, good demo and explanation. I have a question why the condenser trap clogged affect the pressure switch?

[@meerscan9101]

another a1 video! You sure make it simple for new guys coming into trade

[@acservicetechchannel]

Thanks Refrigeration Tech!

[@joellmota8600]

The inducer has positive pressure right blow air to the switch right. ?

[@mark.r8900]

please help as i am a bit confused. as long as the furnace is calling for heat the inducer continues to run. but on a 2 stage gas valve why do we need two pressure switches? one for low heat and one for high heat. many inducers have only one speed. so , the inducer closes BOTH (low and high) pressure switches at the same time on low AND high fire ? is this correct? but it only has one speed. thanks

[@vandalhero]

In this case, even with one speed before switching to high flame you still want to know you have enough draft for proper operation. For example you could have a 1st stage at .5 and second stage at 1.0 but your inducer is pulling only .8 wc, high enough to run 1st stage but not for second stage.

[@stevendennis8225]

Great teaching!

[@acservicetechchannel]

Thanks Steven!

[@yonofui9682]

Teacher you don’t have for sale the fitting for the big hose that connects the gage maniful

[@acservicetechchannel]

If you are talking about the brass barbed fitting with the threads or the brass barbed tee, I have them linked at www.amazon.com/shop/acservicetech

[@geojor]

great teaching videos, thanks ...

[@acservicetechchannel]

I appreciate it!

[@kevinkevin9448]

Are pressure switches interchangeable as long as water column is same ???

[@acservicetechchannel]

Yes as long as they are the same amount of ports and type and also the same small orifice insert at the inlet that the original one had, thanks

[@mazyarkhanlar8134]

I have question , When inducer motor works ,pressure switch closes ,igniter gets red but no voltage to gas valve , When I separate the 24 volt wires from gas valve

[@mazyarkhanlar8134]

Hello , I have question , I have furnace ,the inducer runs ,the pressure switch closes,the igniter turns red but no voltage to gas valve , I replaced the board and same problem , But when I disconnect the orange wire (the 24 volt wire from gas valve ,I see that I have 24 volt to the disconnected wire after igniter gets red , What’s the reason , It does not make sense for me ,

[@keitharoo1962]

Very helpful! I think I got it now. Thanks!

[@acservicetechchannel]

Awesome Keith!

[@keitharoo1962]

It worked! I did the stuff you said, found the problem, and the furnace is working again! Thanks!

[@acservicetechchannel]

That is awesome to hear! That is what we are looking for! Thanks!

[@somap8380]

Do the micro-switches contacts get bad (carbon up) in furnaces; as in say microwave appliances.

[@waytospergtherebro]

Anything that involves two parts rubbing up against each other repeatedly is going to fail eventually.

[@estrelladelnorte1308]

0:58 please help, i don't understand when you refer to "negative" inch water pressure, i thought inches of water was actually pressure not vacuum, yous say that switch is 0.3 which is equivalent to 0.0108274 psi, to me negative pressure means vacuum not pressure , doesn't vacuum always refers to inches of mercury?? 0 inches of water= 0 psi

[@acservicetechchannel]

Hey estrelladelnorte1308, so this is different than refrigerant vacuum levels. Our Manometers read in - and + water column levels. This is what our pressure switches are labeled as and this is what manufacturers state in their literature. I understand it is confusing when thinking of it compared to refrigerant pressures, inch hg, psia, and psig, thanks

[@estrelladelnorte1308]

ok .. so when you refer as negative inches of water column ,it is an actual vacuum but measured in inches of water

[@houseofhappiness4987]

I have a 2 stage kelvinator 2 different pressure switches..1.3 and the other is 0.80 is that normal or can you use an 1.3 in place of the 0.80?

[@acservicetechchannel]

You should replace the pressure switch with the exact same size if needed. You may have 2 switches acting as a differential from the flame box to the inducer or you may have a two speed furnace. For safety only replace with the same size, thanks

[@mark.r8900]

hi, today i saw a furnace pressure switch that says 1.0wc PR. i tested and found out that this switch is normally closed. the pressure switch is connected to the condensate trap . the other two pressures were PF (for the gas stages) switches were normally open. is it normal for the 1.0wc PR to be normally closed? thank you.

[@acservicetechchannel]

Hey Mark, most pressure switches are normally open but it is possible to have one that is supposed to be normally closed, in fact there are some like that but they are older with a lot of relays instead of boards. You would need to look at the wiring diagram to see if it is supposed to be NC, thanks Mark

[@jimbola77]

thank you for sharing!!!

[@acservicetechchannel]

Thanks Jimbola77!

[@johnaries9301]

Can you wire a pressure switch backwards?

[@vandalhero]

its a set of NO contacts so no you cannot. Landing 24v hot on NO will produce the same effect once the switch is closed. Signal will still return to the control board through the common terminal.