Blower motor speeds up and slows down

The torque to drive the motor of your electric fan comes from the magnetic field induced in the motor coils when electricity passes through the coils. When the fan slows down and stops, it could simply be because the coils are worn out, but it's often a burned-out capacitor.

The capacitor on an electric fan is called a run capacitor, as opposed to a start capacitor that gives the needed extra torque for some motors to start.

The run capacitor stores charge and delays the current momentarily, which gives the fan rotor time to turn and orient itself so that the induced magnetic force is effective. When the capacitor burns out, the electric current through the coil is too steady to generate torque, and the fan slows down and stops.

The capacitor in a fan is often similar in shape to a resistor -- cylindrical with a wire at each end -- but it's a solid color. You'll usually find it soldered to the coil, although you may have to remove some protective packing to find it.

After unplugging the fan, cutting out the bad capacitor and soldering in a new one with the same capacitance, your fan should resume normal operation. Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Besides having an abiding interest in popular science, Deziel has been active in the building and home design trades since As a landscape builder, he helped establish two gardening companies.

Skip to main content. Home Guides Home Home Improvement. References 1 Hyperphysics: AC Motor. About the Author Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Deziel, Chris. Home Guides SF Gate. Note: Depending on which text editor you're pasting into, you might have to add the italics to the site name. Customer Service Newsroom Contacts.User Name Remember Me? It blows strong and warm.

How to Troubleshoot a Blower Motor Resistor

After sometimes just a few seconds it will slow down and eventually not blow at all. I am leaning toward Resistor issue, but figured i would post to get everyones opinion. A search only found many poeple that had an issue with no speed on anything but 4, but this is not the same. I have the correct fan speed and whichever I select, but it only work for however long it wants to, usually under 3min.

If I switch it back to zero for a few minutes and then back to any speed it will work again for a few seconds to a minute. Thanks -Justin. Williamsville, NY Sounds like you may need a new blower motor. Either the brushes are worn down or the bearings need to be lubricated. Thanks Steve. TDI s : Jetta 5spd.

I agree with Steve. I just had to replace my blower motor last summer and was doing just what you described. I chose "A" Typical failure mode. Not that unusual for that many miles. Thanks, guys. I'm gonna go grab one today. Wish it wasn't 20 degrees out though. Oddly, similar problem. Two days ago, sunny, 15 degrees Celsius, hot in the car, tried the AC in my Jetta withkm for a few minutes.

I shut off the AC then put the blower on max and noticed it slow to a complete stop. I put the switch to off. After waiting a minute, the fan would blow hard, then slow to a stop again. I removed the fan assy and ran it for an hour on a battery charger with no problems.

blower motor speeds up and slows down

It is a bit stiff to turn but I would hate to buy another one only to find it was something else. Why would it do this in the car and not in my basement? Last edited by Looney2uner; May 9th, at Reason: spelling. In the car it is near active heat sources. It may also be due to the power source. In the car you are running it through wires that you are not using when it is out of the car. There may be a high resistance connection somewhere.

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However my guess is still the a resistor or the resistor pack. If it were my car I would have replaced the resistor pack long ago and have been done with it. A resistor pack is an assembly with several resistors to control various speeds. One speed may go out and, depending on the car, you will need to replace one or more resistors or you may need to replace the pack as the individual resistors may not be serviceable.

Engine heat, high resistance between battery and the motor somewhere.This page is for personal, non-commercial use. Without it, the AC system will not be able to circulate any heated or cooled air. The blower motor relay controls the current used to power the blower motor, and is subject to the constant on and off switching. Over time, it can eventually wear out. When the blower motor relay does begin to fail, the vehicle will usually display a few symptoms that alert the driver of a potential problem that should be serviced.

One of the first symptoms of a problem with the blower motor relay is a blower motor that does not function at all. As the relay is the switch that supplies current to the blower motor, if it fails internally, then power will be cut off from the blower motor circuit, causing the motor to no longer function or blow any air from the vents.

One of the first symptoms of a bad or failing AC blower motor relay is a blown AC blower motor relay circuit fuse. If the blower motor relay develops any sort of problem that hinders its ability to properly limit and distribute power, it may cause the blower motor fuse to blow.

Any sort of electrical spikes or excessive current from a bad relay will blow the fuse and cut power in order to protect the system. Another more serious symptom of a problem with the blower motor relay is a burned or melted relay. Relays are exposed to high current loads and can sometimes get hot when they develop problems. In serious cases, the relays may heat up to the point where the interior components and plastic housing of the relay will begin to melt and burn - sometimes even causing damage to the fuse box or panel as well.

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Since the blower motor relay is essentially the switch that directly controls power to the blower motor, the entire AC system will be left unable to distribute its cooled or heated air if the relay fails. They will be able to determine if the car will need a blower motor relay replacementor a different repairto bring full functionality back to your AC system.

This article originally appeared on YourMechanic. Autoblog is partnering with YourMechanic to bring many of the repair and maintenance services you need right to you. Get service at your home or office 7 days a week with fair and transparent pricing. We get it. Ads can be annoying. But ads are also how we keep the garage doors open and the lights on here at Autoblog - and keep our stories free for you and for everyone.

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Fan Speed Adjustment for PSC, X13 ECM, and Variable Speed

And thanks for reading Autoblog.Hey Everyone, I have a Prius and lately, the fan will stop blowing hard on long drives on hot days when the fan is set to High. This happened on a 3 hour trip on the interstate and again when I was driving some back road for about 2 hours. The first time, I noticed the cabin temp was getting hotter so I went to switch the fan speed higher and noticed it was already on high. It was not set to Auto. When I got home, I let the car cool down for about 30 minutes and when I turned on the car, the AC was blowing full speed and was getting cold like normal.

When the fan speed slowed down on its own on the interstate, it was probably blowing at a speed similar to what the fan would normally blow if set to the middle position or maybe even below that. I have no idea why the fan would slow down on its own when set on high.

I also just checked the temperature coming from the vent after running the AC on LO temp for about 10 minutes. It was reading 50 degrees with a digital meat thermometer and 46 degrees with an infrared thermometer. So, when the car is cool, the AC seems to be working fine. Just wondering about the fan speed and the fact that the car gets really warm when it slows down on its own.

blower motor speeds up and slows down

Any help or ideas would be most appreciated. I'm not ready to take it to a dealer, just hoping to figure it out. Yes, it slows down when the fan is on full bars all the way to the right.

The cabin filter is clean. The car has K. Thank you!

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My mechanic was replacing the front brakes for the first time at K nice!! He speculated that the fan motor could be starting to fail so it ends up slowing down when it has to work hard on hot days, but he also said it could be a relay, capacitor, or another problem. I am wondering why the air coming out does not seem as cold when the fan slows down.

Its like the compressor is not fully working and the fan is slowing down to match the compressor. Again, I have no idea though. Yes, my mechanic said he probably could only diagnose it when it is having the problem. His shop may not be the best place to diagnose this issue. I am hoping someone on this forum may have experienced this problem too or might have a pretty good idea of what it may be. I have the same problem withywith k miles. Did you ever figure it out? I wonder if evaporator coils are icing over and blocking airflow.

Bad blower fan. Very very common. I replaced mine at 90, miles. Only use OEM fan. Its the fan underneath the cabin filter. So fun to replace. You must log in or sign up to post here. Show Ignored Content. Similar Threads - Blower Speed Slows.When the truck sits and idles the blower works fine but when your driving and start to pull a hill the blower slows down when the truck is at about rpms nothing really is coming out of the vents as soon as you let off the accelerator it picks back up to normal.

The blower motor is not slowing down. What is actually happening is the mode control for your AC and heat is losing its vacuum source. Engines do not produce intake vacuum when under load. To overcome this, there is a vacuum reservoir and a check valve to maintain vacuum in the HVAC system so it still functions when the engine is under load.

The reservoir is just a plastic ball. It could be cracked, the hose is off, or the check valve could be bad. If your S10 is 4WD, there is a lot more testing involved.

The transfer case and the front axle are both controlled by vacuum. The vacuum switch on the transfer case is known to fail. When it fails, engine vacuum pulls transfer case oil into the system. In summary, this could be an easy fix, a vacuum line off, or a cracked ball. It could also mean checking and repairing a lot of components. The fact that your HVAC works at idle points towards an easy fix.

What Is Causing the Motor on an Electric Fan to Slow Down and Stop?

Good luck. When the truck sits and idles the blower works fine but when your driving and start to pull a hill the blower slows down when the truck is at about rpms nothing really is coming out of the vents as soon as you let off the accelerator it picks back up to normal My car has miles. My car has an automatic transmission. Daniel Barker Automotive Mechanic.

Thank Daniel.

AC Blower Speed Slows Down On its Own When Set to High and Running Car for A While

Was this answer helpful? Thank you for your feedback! Sorry about that.The most common symptom of a faulty blower motor resistor is a blower fan that only works on one speed, usually high. This can be annoying, but troubleshooting is easy. If you start at the blower motor, and check resistance in the circuit, you will find the problem in no time.

Power supplied from the fuse panel passes through the switch to the blower resistor assembly. The switch supplies ground to the different resistors in the assembly, depending on the speed selected. The added resistance in the circuit slows down or speeds up the blower motor as needed.

blower motor speeds up and slows down

Test the fuse, with the ignition key on, using the volt test light. Attach the clip lead of the test light to a good ground like a bolt screwed into metal, and touch the sharp probe end to the terminals on the fuse. An indication of power at both terminals of the fuse determines that the fuse is good.

If one of the terminals has power and the other does not, the fuse is bad. Replace the fuse as needed. Unplug the blower motor and test for power using the volt test light in the same manner as explained in Step 1. Testing at the motor itself eliminates the possibility of confusion caused by complicated electronic blower controls found in Electronic Climate Control systems.

Test for power at all the blower speeds by moving the blower speed switch through all positions. A faulty resistor loses power at different positions on the switch.

High blower speed has direct power to the motor from the switch. If there is no power indicated on high blower speed, the problem is most likely the switch or the fuse. If there is power indicated on high blower speed, but not low or mid range, the problem is the blower resistor. Test for ground at the blower motor if there is power indicated at all ranges, but the motor does not function. Most blower motors ground through the case of the motor when it is screwed into place or by a small ground strap from the case to the body of the car.

Over time, the ground connection can become corroded or loose, causing the motor to function intermittently. This article was written by the It Still Runs team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.

To submit your questions or ideas, or to simply learn more about It Still Runs, contact us. Step 2 Unplug the blower motor and test for power using the volt test light in the same manner as explained in Step 1.

About the Author This article was written by the It Still Runs team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.Electric motors run maintenance-free most of the time; many are self-lubricating and only occasionally require the oil wells to be topped up.

Many of the parts in an electric motor are effectively non-serviceable as a do-it-yourself task, such as the windings, but you can replace the brushes that make contact with the armature.

Blower motor slowing down and speeding up - help please

Worn brushes are often responsible for a motor that turns slowly, as the contacts break down and current can't be applied. Pry out the ring clips from the brush holder using a screwdriver and a pair of pliers.

They are usually on the back of the electric motor. Pull out the two metal springs from their retainers and then remove the brushes. When they are worn there is very little to remove, but make sure they are out completely.

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Insert new carbon brushes into the retainer compartment; push them in using your fingers. Insert the springs behind the brushes. They won't go totally inside the retainer due to the size of the new brushes. Push the springs into the retainer using a screwdriver, then insert the ring clips into the retainer.

This holds the springs and brushes in place. Start your electric motor. You will find it sparks for a while around the brushes until they bed in. Your motor won't operate at full power immediately, but leave it running for a while and once the brushes are bedded in the motor will operate normally. James Stevens has been writing articles for market research companies in the U.

He has written various country profiles for inclusion in comprehensive market reports including Vision One Research and Investzoom Market Research. Hunker may earn compensation through affiliate links in this story.

A screwdriver is genarrly all you need to get your motor working again. Step 1 Pry out the ring clips from the brush holder using a screwdriver and a pair of pliers. Step 2 Pull out the two metal springs from their retainers and then remove the brushes.


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