{"id":3581,"date":"2026-10-22T02:36:00","date_gmt":"2026-10-21T18:36:00","guid":{"rendered":"http:\/\/www.mytets.com\/blog\/?p=3581"},"modified":"2026-10-22T02:36:00","modified_gmt":"2026-10-21T18:36:00","slug":"how-do-i-test-furnace-accessories-475d-075ef4","status":"publish","type":"post","link":"http:\/\/www.mytets.com\/blog\/2026\/10\/22\/how-do-i-test-furnace-accessories-475d-075ef4\/","title":{"rendered":"How do I test furnace accessories?"},"content":{"rendered":"

Hey there! If you\u2019re a furnace tech, HVAC shop owner, or just someone who\u2019s been stuck trying to figure out why their furnace\u2019s draft inducer\u2019s acting up, you know furnace accessories make or break how well the whole system runs. I\u2019ve been selling furnace accessories for over 8 years now, and let me tell you\u2014one question I get way more than any other is \u201cHow do I actually test these parts to make sure they don\u2019t quit on me mid-job?\u201d No more guessing games, let\u2019s break this down like we talk in the shop\u2014no stuffy engineering jargon, just real, usable steps I\u2019ve tested myself a hundred times. Furnace Accessories<\/a><\/p>\n

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First off, let\u2019s get one thing straight: testing furnace accessories isn\u2019t just for when something\u2019s broken. You should be doing pre-install checks too, right? I\u2019ve had a brand-new draft motor come in from a batch that was dead out the box\u2014stuff happens. So before you even slap it into a furnace, run through these quick tests. Let\u2019s start with the most common accessories people mess up on: draft inducers, limit switches, flame sensors, and pressure switches. Those are the big four that cause 90% of furnace headaches, so we\u2019ll focus there.<\/p>\n

First up: draft inducer motors. These little guys pull exhaust fumes out of the heat exchanger, so if they\u2019re not working right, you\u2019re looking at carbon monoxide backup\u2014super serious stuff. How do I test one? I don\u2019t just plug it in and hope it spins. Here\u2019s my go-to method. First, a visual check: look for any frayed wires, burnt spots on the housing, or bent fan blades. If the blades are all warped, even if the motor runs, it\u2019ll be lopsided and create too much draft, which kills efficiency. Next, the voltage test\u2014easy with a multimeter, everyone should have one of these. Turn the power off to the furnace first, duh, safety first. Disconnect the wires going to the inducer motor. Set your multimeter to AC voltage (most residential furnaces use 120V or 240V, but always check the part label). Touch the multimeter probes to the motor\u2019s wire terminals, then turn the power back on just long enough to read the voltage. If it\u2019s not matching what\u2019s listed on the motor (say it says 120V and you get 100V), the motor\u2019s not getting enough power, and that\u2019ll cause it to underperform. Then, continuity test to check if the windings are shot. Switch your multimeter to continuity mode (beeps if there\u2019s a closed circuit). Touch the probes to the motor\u2019s two terminals\u2014if it doesn\u2019t beep, the windings are burned out, toss that motor. Last, spin the fan blade by hand\u2014if it\u2019s stiff or grinds, the bearings are bad, even if it runs. I\u2019ve sent so many return requests for motors that passed the voltage test but had bad bearings\u2014this quick spin test catches that.<\/p>\n

Next: flame sensors. These little rods are what tell the furnace \u201chey, there\u2019s fire, keep the gas on\u201d\u2014if they\u2019re dirty or broken, the furnace will shut off mid-cycle, leaving your customer\u2019s house cold. Testing a flame sensor is simple, no fancy tools needed. First, pull the sensor out (it\u2019s usually a \u00bc\u201d hex head bolt on the burner assembly). Look at the end\u2014if there\u2019s a thick crust of black gunk on it, that\u2019s the issue. Wait, but don\u2019t just clean it and call it good\u2014test it first. Here\u2019s how: after pulling it, turn the furnace\u2019s power on, hold the sensor close to the burner (where it would pick up flame), and use a multimeter set to microamps. Touch one probe to the sensor, the other to a ground on the furnace frame (like a bolt). For a working sensor, you should get a reading between 3 and 10 microamps. If it\u2019s zero, the sensor is dead, no signal getting sent. If it\u2019s less than 3, it\u2019s dirty\u2014sand the end with fine steel wool (never use sandpaper, it leaves residue) and test again. I always tell guys: if the reading\u2019s still low after cleaning, replace it\u2014don\u2019t waste time. I\u2019ve seen a tech scrub a sensor three times when he just needed a new one, and he lost a service call because it took too long.<\/p>\n

Limit switches\u2014these are the safety thing that turns the blower off if the furnace gets too hot, so they\u2019re non-negotiable. If a limit switch fails, it can cause overheating, which is a fire hazard. How to test these? Again, safety first: turn power off. Limit switches are usually near the heat exchanger, with two wires. First, test continuity when it\u2019s cold. Set your multimeter to continuity mode, touch probes to the two switch terminals. It should beep\u2014if it doesn\u2019t, the switch is already open (bad). Then, to test if it trips at the right temp: the limit switch has a little lever you can actuate. Gently push the lever to trip it\u2014if after pushing it, the multimeter stops beeping, that means it works (it should open when tripped). Wait, but how do you know it trips at the right temp? If you\u2019ve got a heat gun, warm the switch up (don\u2019t melt the plastic!)\u2014when it reaches its rated temp (check the label, usually 150-200\u00b0F), it should trip and stop continuity. If it doesn\u2019t trip when it\u2019s supposed to, that\u2019s a bad switch\u2014you can\u2019t adjust these, they\u2019re preset. I\u2019ve had customers try to \u201ctweak\u201d a limit switch before, which is a terrible idea\u2014just replace it.<\/p>\n

Pressure switches\u2014oh man, these ones get so many calls about. They make sure the draft inducer is working before the furnace starts, so if the exhaust isn\u2019t pulling right, the switch stays open and the furnace won\u2019t light. Testing a pressure switch is a little trickier, but I do it all the time. First, locate the two tubes connected to the pressure switch\u2014one is a \u201cstatic\u201d tube, one is a \u201cdraft\u201d tube. Make sure those tubes aren\u2019t clogged with dust or spider webs\u2014spiders love to build nests in those tiny tubes, and that\u2019s the number one cause of pressure switch issues. Clean the tubes out with a small brush (even a pipe cleaner works) first. Then, test continuity. With the furnace power off, disconnect the wires to the pressure switch, set multimeter to continuity. Touch probes to the switch\u2019s terminals\u2014what you get depends on the type. For a \u201cnormally closed\u201d pressure switch (most common), it should beep when the inducer isn\u2019t running. Now, run the inducer manually (you can jump the wires at the inducer to turn it on without the furnace) \u2014 when the draft is created, the switch should trip and stop beeping. If it doesn\u2019t, the switch is bad, or the tubes are still clogged. Another quick test: if you have a spare pressure switch, swap it in and see if the furnace works. I keep a few spares of the most common pressure switch models on hand for exactly this\u2014no need to overcomplicate it with fancy tools.<\/p>\n

Wait, let\u2019s not forget smaller accessories\u2014like furnace filters, blower belts, and ignition transformers. Those are the ones people overlook, but they\u2019re just as important. For filters: test fit. I\u2019ve had filters that are labeled \u201c1-inch\u201d but are slightly too big and warp, or too small and leak dust. When you slide it into the slot, it should fit snug, no gaps around the edges\u2014if there are gaps, it\u2019s useless, get the right size. For blower belts: stretch test. Pull on the belt\u2014if it stretches more than \u00bd inch when you push it, it\u2019s too loose. If it\u2019s cracked or frayed, replace it. I always tell guys: change the belt when you change the filter, that\u2019s a easy combo to remember. For ignition transformers: test output voltage. Disconnect the wires, set multimeter to AC voltage, touch probes to the transformer\u2019s secondary terminals (the ones that go to the igniter). It should match the label\u2014usually 12,000V for spark igniters. If it\u2019s way lower, the transformer is dead, and your igniter won\u2019t spark.<\/p>\n

Now, a few pro tips I\u2019ve picked up over the years. First, always reference the part number. A lot of guys grab a \u201csimilar\u201d accessory and it doesn\u2019t fit, so testing won\u2019t help if it\u2019s the wrong part. I\u2019ve had people come to me with a part they bought elsewhere, saying it\u2019s broken, and it turns out it\u2019s for a 80% efficiency furnace, not their 95%. Second, document your tests. I keep a little notebook for my own orders\u2014if a batch of 10 draft motors had two bad ones, I note that so I can check the next shipment extra careful. Third, test accessories individually before installing them into a full furnace. If you test the limit switch and it\u2019s bad before you mount it, you don\u2019t have to take the whole furnace apart to fix it\u2014save yourself the hassle.<\/p>\n

Look, I get it, testing accessories can seem like a chore, but it\u2019s way cheaper than dealing with a service call where a part failed mid-install, or worse, a carbon monoxide scare from a bad draft inducer. At the end of the day, a furnace system is only as good as its parts, so making sure each accessory works before you put it to use is just good business\u2014for you and your customers.<\/p>\n

If you\u2019re tired of guessing if your furnace accessories are gonna work, or if you need reliable, tested parts that pass my own shop\u2019s checks before they leave here, hit us up to talk about bulk orders or specific part needs. We\u2019ve got all the accessories I mentioned\u2014draft inducers, flame sensors, limit switches, pressure switches, and more\u2014at prices that won\u2019t break the bank. No hidden fees, no parts that die out the box, just stuff that works when you need it.<\/p>\n

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Oh, and one last thing: never skip safety. Always turn off power to the furnace before testing any electrical parts\u2014you don\u2019t want to get shocked. And if you\u2019re not comfortable working with electrical components, call a pro, but if you are, these steps work every time.<\/p>\n

Resistance Furnaces<\/a> Reference
\nASHRAE Handbook\u2014HVAC Systems and Equipment, American Society of Heating, Refrigerating and Air-Conditioning Engineers
\nFurnace Installation and Service Manual, National Comfort Institute
\nHVAC Troubleshooting Guide, United Association of Journeymen and Apprentices of the Plumbing and Pipe Fitting Industry<\/p>\n

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Zhejiang Changxing Qingfeng Electric Furnace Co., Ltd.<\/a>
We’re well-known as one of the leading furnace accessories enterprises in China, specialized in providing high quality customized service. Please feel free to buy discount furnace accessories made in China here and get pricelist from our factory. For price consultation, contact us.
Address: No. 306, Wushangang, Lincheng Town, Changxing County, Zhejiang Province
E-mail: 13905822510@163.com
WebSite: https:\/\/www.qfdlindustry.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

Hey there! If you\u2019re a furnace tech, HVAC shop owner, or just someone who\u2019s been stuck … How do I test furnace accessories?<\/span>Read more<\/a><\/p>\n","protected":false},"author":462,"featured_media":3581,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3544],"class_list":["post-3581","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-furnace-accessories-461a-07970a"],"_links":{"self":[{"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/posts\/3581","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/users\/462"}],"replies":[{"embeddable":true,"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/comments?post=3581"}],"version-history":[{"count":0,"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/posts\/3581\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/posts\/3581"}],"wp:attachment":[{"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/media?parent=3581"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/categories?post=3581"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/tags?post=3581"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}