Where is pressure switch in furnace

We recommend shutting off the gas supply as well. Pressure switches are normally located in the combustion chamber, close to the draft inducer fan motor. To reach it, you will need to uninstall the upper access panel. Disconnect the pressure switch wires, along with the vacuum tube or tubes. Next, unthread the mounting screw, or screws, to release the old pressure switch from the draft inducer fan motor housing or bracket.

When installing a new pressure switch you should confirm that the pressure rating matches the rating found on the original. Ratings will differ depending on your geographic location. Position the new switch on the fan motor, the housing or the bracket as required. Thread the mounting screw or screws to secure. Image of a pressure switch connected to the inducer fan housing on a furnace. The pressure switch in your furnace is used as a safety mechanism.

It is there to confirm the unit is drafting properly. If the unit is not drafting properly, then it does not operate as efficiently and creates a safety risk by not removing unwanted gases that can make us sick or cause small explosions inside the heat exchanger.

This is why if the pressure switch isn't satisfied with the right amount of suction, it will not allow the unit to ignite. Different furnaces may have different types of pressure switches in them.

Based on the size of the unit meaning heat output capability, not the physical dimensions , the amount of suction the pressure switch requires to work will vary. But when talking about high and low pressure switches, it typically has to do with the number of stages a unit can operate in.

While many of us still have a single stage furnace that runs at full capacity every time it turns on, there are two stage units that will run at a lower heat output, and then when needed, it will kick into a 2nd stage for more heat.

These types of furnaces require a dual pressure switch so it can monitor the level of suction in low fire and then another in high fire since they require different amounts of ventilation to function properly. Some two stage furnaces will use what is commonly referred to as a pancake switch since the two pressure switches are "pancaked" together while others will have two separate pressure switches.

Either way, one of these switches is called the low pressure switch and the other a high pressure switch. This is what a "pancake" type pressure switch looks like and if you need to replace it you just replace them both since that is likely how you will have to buy it.

The table above gives you quite a few causes of pressure switch failure that are easily confirmed or eliminated as the problem either audibly or visually.

You should start with checking those things since they are the easiest, don't require special tools, and cost nothing. If you've taken a few minutes to rule these things out and still have a problem, then we can confirm the switch is bad by testing the circuit with a voltmeter and maybe get the unit working temporarily for a little heat at least.

Voltmeter showing resistance meaning our pressure switch is closed and since there is no vacuum, it shouldn't be and therefore has shorted. The actual work involved in replacing a pressure switch is quite simple and doesn't require any specialty tools that you don't likely have laying around the house.

Like many furnace components, the pressure switch is not an item typically found in the "big box" stores like Lowe's and Home Depot. To find a replacement, you will likely have to do one of two things: contact the contractor supply house that sells your brand of furnace or obtain a universal replacement from a contractor supply house or online.

Furnaces are much like cars and have parts that are specific to their brand. That is why if you want a direct factory replacement, you have to find the supplier that carries your brand.

It's a "don't call a Chevy dealer for Ford parts" sort of thing. Once you've found the supply house that carries your brand, be prepared to tell them what part you are looking for and have your unit's model and serial number handy so they can help you.

That said, many of these suppliers are "contractor only" and will not sell to the general public so the more prepared you are, the more likely you are to get them to sell to you or at least give you a part number so you can look online for it. A universal pressure switch, however, may be easier to find and purchase at any supply house or online. I keep this NS2 universal pressure switch handy so that if my or a family member's unit breaks down at an inopportune time, I can make the repair without going hunting for one.

These are nice because they can handle single stage and dual stage units as well as be set to various pressures. They also contain brackets that make mounting possible in more than one unit. The instructions walk you through the process of setting up the switch to suit your unit's needs. I hope the information I've given you regarding your furnace's pressure switch has helped you deduce whether or not the pressure switch is the problem you're having or if another part was a cause.

If your still not sure what's going on, then I recommend you contact a technician. We don't want to make matters worse or get in over our head. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Question: My vent pressure switch is working fine. I replaced the ignitor already. Is the furnace control module my next step? While replacing parts will eventually get you there and perhaps even end up still saving you money vs.

Using your meter, you can trace the 24 volts coming from the control board, through the safeties, and on to the pressure switch. Place one lead on ground or a solid piece of metal attached to the furnace. Place the other on the incoming terminal of the switch. If you have 24 volts on the incoming terminal but not at the terminal leaving the switch, you can assume the pressure switch has not closed. The required suction is listed on the pressure switch.

Once you put the hose on and start the system up, the inducer comes on, and the manometer should start reading the induced draft as it begins to rise. This number on the meter needs to be greater than the number on the pressure switch.

On the collection chamber, check to see if the port itself is clear of any calcium deposits, dirt, or other debris that would prevent air from flowing through the port. If there is, take a small wire — like some thermostat wire — and clean that port out. Whatever the substance is, it should be brittle enough to be scraped off, allowing the port to become clear. Remember, the inducer motor causes a draft to allow the gasses to be drawn out of the heat exchanger and into the flue pipe where it terminates outside the building—usually the roof.

I have found that bees, wasps, and birds like to build their nests in and around the flue pipe. Commonly, the pressure switch fails because the diaphragm inside the casing has become stuck or it has ruptured. Ruptured diaphragms can sometimes make a flapping noise. But your switch is on borrowed time, and nine times out of 10, the switch will fail again. If I tell you it will fail tomorrow, it will last for years. I recommend trying to convince the customer to replace the pressure switch now, so there are no surprises.

One way to see if the pressure switch is stuck open or closed is to breathe lightly into the hose leading to the switch. But, the pressure switch would still not send 24 volts across to the other terminal. Is the hose itself in good condition? Rats like to chew these hoses up and leave holes in them.