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Bryan explains how to install and adjust belts. Belt tensioning is a critical part of commercial HVAC work, though they’ve slowly been disappearing as blower motors and fan motors become more direct-drive.
A common belt myth is that you need to tension a belt so that it has an inch of deflection. Many factors can affect deflection, including the pressure you apply to the belt, the belt’s length, and what the belt is made of.
There are no hard, fast rules of thumb for working with belts. However, we recommend using the Browning app to help you if you’re unfamiliar with belts and typical procedures with them.
If you’re working with an adjustable drive pulley (sheave), DO NOT adjust the pulley itself to set the belt tension. Instead, you have to adjust the foot mount on the motor to set the belt tension. Before you replace the belt, check the pulley condition; the problem could lie there, not with the belt. Replace the pulley if it is damaged.
When you adjust the two halves of the pulley closer together, you can expect more airflow. When you adjust them to sit further apart, you decrease the airflow. So, you must measure airflow to set those halves correctly. We don’t typically adjust those in the field, but we have to adjust the motor base inward if we want to replace a belt.
When the old belt comes off, we want it to be loose. Of course, we must also put the new belt on loosely and tension it appropriately once we finish the replacement. You’ll want to avoid overtightening the belt, so a tensioning tool will be especially effective here.
A proper tensioning tool allows you to apply a set amount of force and then look at a fixed amount of deflection. Browning makes a tool specifically designed for this purpose. (Product link:
You should not set your belt tension based on blower amperage; the blower motor could run well below its peak conditions. Instead, you want the belt to be as tight as possible without slipping or squealing under peak-load conditions. Overall, if you need to do significant adjustments, you may as well replace the belt. Always inspect the whole system if there is slippage, too.
Browning belt tensioning instructions: #view_8082E
Browning video on How to Check if your V-Belt is Properly Tensioned:
Read all the tech tips, take the quizzes, and find our handy calculators at
Learn more about the 2022 HVACR Training Symposium at

A lot of technicians in the commercial market have to install and adjust belts, and these fan belts are getting less and less as blower motors and fan motors. Get it to be more and more direct drive. But you still see a lot of them out there and knowing how to install them and adjust them is going to be really key to your success now. The first thing i want to do is dispel some myths.

A lot of people will say things like you want to tension a belt until it has half inch of deflection or one inch of deflection. But that really can't be the case, because obviously it would depend on how hard you squeezed, how strong your hands were and how long the belt was, what type of belt it was for that rule to make sense. So a lot of technicians have come up with you know, sort of calibrated fingers as far as what is and is not the correct tension for a belt. So there are no simple rules of thumb, but you do have to know a little bit about belts before we can go any further.

The first is, i suggest that you get the browning app browning does a great job of describing how all of this works. They also have some tools that will help you tension, so reference their information as much as possible. If you have an adjustable drive, pulley a lot of people, call it a shiv or you know it's kind of spelled like sheave. If you have one of those adjustable drive, pulleys do not adjust the adjustable drive pulley.

In order to set the belt tension, you set the belt tension by adjusting generally, it's going to be the foot mount of the motor in order to tension and untension make sure before you replace a belt or if you have a belt, that's squealing before you adjust It that you've actually inspected the drive and the driven pulley to ensure that the pulley itself is in proper condition. In many cases, the pulleys will actually get worn out. So they'll have a really smooth surface or they'll be an incorrect shape. You can get a pulley gauge to actually see if it is worn or not, but many times you can just do that just by paying attention to it kind of rolling around looking for ridges or damage to the pulley.

If you do have a damaged, pulley you're going to want to replace the pulleys and you're going to want to do that sooner than later before they start eating up a bunch of belts or before you get squealing or things like that here on this image, you Can see some of the different components to the adjustable drive pulley, the one that we call the the shiv and with the adjustable drive pulley adjusting the two halves of the pulley closer together results in more airflow and adjusting it further apart results in less that's only Something a test and balance organization or somebody who's doing a commissioning with set, or maybe a retro commissioning, because you have to measure airflow in order to do that properly in the field. We are not going to be adjusting that adjustable drive pulley, but if we are going to replace a belt, the right thing to do is to adjust it inward adjust the motor base inward. So that way the belt gets loose or put the new belt on and then re-tension it appropriately and the best way to do that is with a tensioning tool. Now i know a lot of you won't be using a tensioning tool, but again i suggest you use the browning toolbox.

Technician app and browning uses this line in the app which i think is brilliant. It says ideal tension is the lowest tension at which the belt will not slip at peak conditions, meaning when that motor is starting. That's generally, when it's going to have that kind of peak load on it, you don't want that motor to slip or squeal. If you've ever heard a belt, that's squealing! Whenever the motor starts, you can know how annoying that can be, and that creates further wear to the pulleys.

But you don't want it any tighter than that. A lot of technicians will incorrectly state that you're supposed to set belt tension based on blower amperage and that's a terrible idea. The belt tension is placing some forces onto that blower motor shaft, but potentially and as you as you know, with many other motors that motor could run. You know decent level below its full load, amperage based on how the adjustable drive pulley is set and if you are tensioning it so tight that you're actually binding down those bearings and making the motor draw a higher amperage you're doing damage to the motor and motor Bearings, the pulleys, the belt everything else so do not over tighten the belt.

You want to get it just tight enough. So that way, there is no squealing and no slipping even on start, but no tighter than that now again, because they can start to kind of wear in pretty quickly technically you're supposed to go back and adjust within a few hours of initially running it or a Few days - and you know we know - that's probably not practical in a lot of cases unless you're in a maintenance environment where you're maybe doing facilities and you're always at the same site. So you may be a little bit tighter than that. But you don't want to stretch belts out.

You also see a lot of text, go back and keep adjusting belts and stretching them and stretching them. If a belt is stretched enough, that you need a significant adjustment, then you need to go ahead and just get a new belt and then also pay attention to that pulley and pulley condition. Now again, a proper tensioning tool allows you to apply a set amount of force and then look at a fixed amount of deflection and again, browning has some great videos on this, and they have a tool specifically made for this purpose that you can use again refer To their application, a lot of technicians again aren't even aware that this exists i suggest to attack even if you're not going to use it every single time. Do it on several occasions until you can get used to what the proper tensioning is for that particular belt.

With that particular width, because there is so much variation using a rule of thumb like half inch deflection, just makes no sense, because you don't have a fixed amount of force that you use. So that's it when you're replacing a belt. Make sure that you loosen it all up so that way, you're not stretching the belt to roll it on or roll it off, don't adjust the belt significantly. If you need significant adjustments, then just get a new belt inspect your pulleys do not adjust an adjustable drive.

Pulley in the field, unless you're doing something like a retro commissioning or a test and balance an application where you're actually measuring airflow and making sure that it fits and do not over tighten a belt. So that way, you're binding down on that motor. The old line that we set our belt tension based on blower motor current could not be more incorrect. Final thing, i'll mention is that in some cases you get slippage and that sort of thing just because of the conditions around the belt, whether it's greasy or oily.

If you have anything like that, make sure you clean it and make sure you address the source of the problem before just constantly adjusting or replacing belts so install your belts, properly tension them properly and pay close attention to police and you'll be just fine thanks for Watching our video, if you enjoyed it and got something out of it, if you wouldn't mind hitting the thumbs up button to like the video subscribe to the channel and click, the notifications bell to be notified when new videos come out, hbac school is far more than A youtube channel you can find out more by going to, which is our website and hub for all of our content, including tech tips, videos, podcasts and so much more. You can also subscribe to the podcast on any podcast app of your choosing. You can also join our facebook group if you want to weigh in on the conversation yourself thanks again for watching you.

28 thoughts on “Hvac belt tension”
  1. Avataaar/Circle Created with python_avatars Terry Graham says:

    Some techs need to learn how to align the pulley. Make one for that. Service area Kanata??

  2. Avataaar/Circle Created with python_avatars georgio jansen says:

    how does the gates ultrasonic works

  3. Avataaar/Circle Created with python_avatars Roommate625 says:

    Tampered with adjustable sheaves can trip motor overloads because motor is trying to push too much air.

  4. Avataaar/Circle Created with python_avatars Edward Moore says:

    Why can I never get multi-belt systems to have the same tension on every belt? One is always slack no matter how much I line up the two sheaves…!

  5. Avataaar/Circle Created with python_avatars yafiteli says:

    I would like to see a video about charging a system in low temperatures where you have to partially block or tent the condensing unit.. I would also like to see a video about two stage air conditioners. Is a different TXV used or does the air handler just modulate the air flow?

  6. Avataaar/Circle Created with python_avatars yafiteli says:

    Great video. Sometimes it's the little things we overlook that we need most.

  7. Avataaar/Circle Created with python_avatars K Marrast says:

    The modern refrigeration and air conditioning book is key on learning about belt tension…one side should be running smooth while the other side should have a slight flapping to it…hope I explained it right.

  8. Avataaar/Circle Created with python_avatars diamond_boots says:

    Had a fun one today:

    – Unit would run for a couple hours and shut off.
    – VFD showing the error code for motor thermal overload, and locking out.
    – Motor not getting hot at all.
    – 3 of the rooms with returns for the unit had outside doors that were constantly opening. (In HOU, so this means adding humidity too)
    – Megger would read bad leads immediately following a lockout, but given a little time it would return to a good reading.

    Anyone wanna take a stab at what it was? Are you in Nepean ?

  9. Avataaar/Circle Created with python_avatars José Cruz says:

    Being in S.FL and the FL. Keys. Most of the time I was adjusting the speed and the charger but now after this.🤔🤔🤔😎 I will follow the recommend advice 👌👍😉😀 thanks 😊

  10. Avataaar/Circle Created with python_avatars Bobo Logic says:

    no mention of alignment or checking the motor amps to prevent overcurrent motor damage

  11. Avataaar/Circle Created with python_avatars Dan Ennis says:

    Tensioning practice is key but if you leave an adjustable sheave in place you're asking for belt alignment issues. Every belt change you should be checking the belt alignment as well as tension. It is also wise to check the rpm of the driven pulley after initial commission or T&B has been done so you can make sure it doesn't change when you you replace a belt or against standards adjust or replace the adjustable sheave. Belt tensiok is only the tip of the iceberg if you want to do it properly

  12. Avataaar/Circle Created with python_avatars Adam Bergmann says:

    If the motor is over amping you can adjust the sheave to reduce amperage correct ? A 50 year old nursing home I recently went out there

    The motor had been replaced recently was spinning the wrong direction and more than double fla. the hood filters get sucked up against to roof of the hood. MAU Gutted make up air. Who knows what the original hp motor and cfm was, but I did check the up draft in the hood by pouring a pitcher of water on the hot grill to make sure it was all going up in the hood even after reducing the amps in half to below name plate.

  13. Avataaar/Circle Created with python_avatars OcRefrigeration , Hvac & Electrical Video's. says:

    Good Topic ! Good video. ( Ftngot ) after doing this for 40 years ive found that overtightning a Belt WILL Do Far More damage than a Slightly loose Belt.
    Overtighning – WILL damage / destroy Bearings
    Undertightning – a Belt May slip at times. creating little to no damage. maybe a Pulley replacement overtime. alot cheaper than bearing job or motor replace.

    ive Learned in 40 years to just replace Belts When they get stretched. i No Longer adjust inexpensive belts anymore.
    Cheaper for customer & better.

    also – when possible – use a belt tensioning guage as seen in this video to get it right from the get go.

    Tech tip – Clean the Groove – Use a Wire brush & use sandcloth to remove the shine off Belt Pulleys for a better Grip.

    Tech. tip #2 – a Cog belt will Get a Better grip than a standard belt. Try a cog belt if u have one that slips under proper tension.

  14. Avataaar/Circle Created with python_avatars Zach Lenning says:

    Here's a tip I learned from my Boss, even though he isn't a mechanic. He learned it from a mech in AZ. I've used it successfully a number of times. Presuming the pully isn't totally warn out, just shiny, you can clean it and re paint it. I use rattle can primer and rust oleum. Works well, I have fixed rigs that would slip the belt no matter how tight( new belt ). Down side is it needs to dry for a day. But, if you can't get a new pully for some reason….

  15. Avataaar/Circle Created with python_avatars Vieux Acadian says:

    1/2 inch deflection per foot in shaft centers length was what the USAF taught Us decades ago on cv non vs drives Are you in Orleans ?

  16. Avataaar/Circle Created with python_avatars Ian Frye says:

    Don’t roll on or off the belt… every tech in the field 👀👀👀

  17. Avataaar/Circle Created with python_avatars This Is Your Captain Speaking says:

    Overtightening a belt will cause all kinds of damage and can get expensive. Undertightening will result in slippage, which is usually detectable.

  18. Avataaar/Circle Created with python_avatars Ty Branaman says:

    spot on! I did not know about the pully gauge, added to the tool list.

  19. Avataaar/Circle Created with python_avatars Mark Caldwell says:

    Ouch hard when a school teaches it is a pulley. Maybe the video should start with the definition of a sheave, lol. But then my instructor was a bit of a ball buster. Service area Barrhaven??

  20. Avataaar/Circle Created with python_avatars Brian Mcdermott says:

    Great tips. Thanks Bryan

  21. Avataaar/Circle Created with python_avatars Waylon Wells says:


  22. Avataaar/Circle Created with python_avatars Kain Ivester says:

    I always check for misalignment with a straight edge because it may look like it's tracking but off just a little, prematurely wearing the belts or pulley.

  23. Avataaar/Circle Created with python_avatars Eassyheat/ Cooling says:

    Beer can cold and calibrated fingers ,welcome to the institutional maintenance program.
    Stay safe.
    Retired (werk'n)keyboard super tech. Wear your safety glasses.8

  24. Avataaar/Circle Created with python_avatars Ty Huffman says:

    Good job Bryan thanks for bringing this topic up. My $0.02 – First decide which you, and your customer, would prefer to replace the belts or the motor. Belts are cheap, replace them e'rry 6 months, preferably during the biannual inspections. If the belts are set too tight the bearings will take the hit due to load, if the belts are sloppy loose or the sheaves are worn the bearings will suffer due to shock. If the belt is riding on the bottom of the sheave the sheave needs to be replaced, the belt should ride on the sides of the sheave. When rolling the fan the belts should fide smoothly through the sheaves, if the belts get stuck in the sheave the sheave needs to be replaced. Most belts are made of Kevlar so that belt dust will eat the bearings if it gets in them. Never roll belts on or off, that can set them up to do weird things like flipping over while running. ->I've seen that.

  25. Avataaar/Circle Created with python_avatars Attest411 says:

    Ahh. “It’s an $11 belt. As long as and the sheaves are aligned. Tension will wear the belt and PM contract will cover a new belt”

  26. Avataaar/Circle Created with python_avatars Christopher Smith says:

    I needed this. Thank you Bryan.

  27. Avataaar/Circle Created with python_avatars Wiggie says:

    Hey Brian great video do you think you can post more on commercial units and RTU like this one

  28. Avataaar/Circle Created with python_avatars Savant218 says:

    Yea, right. they make it easy using their shit metal mounts that flex and bend under the torque of the motor.
    Fck Carrier for sure
    Their all sht !!!

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