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Photograph of attic air conditioning air handler, condensate drips on floor Air Handler Blower Fan Speed
Jumpers / Switches / Controls for Fan Speeds & Functions

  • POST a QUESTION or COMMENT about how to diagnose & repair problems with the air handler or blower unit / fan assembly in a warm air furnace or air conditioning system

How to set the fan speed in your heating or air conditioner air handler unit or "blower unit" .

How is the blower fan or air handler fan speed controlled in heating and air conditioning air handler equipment or split systems air AHUs?

This article series explains how to inspect & repair the indoor components of air conditioners and heat pumps: the air conditioning system indoor air handler units, blower units, or AHU's, (also called fan coil units) including the air conditioner blower fan, the indoor cooling coil or "evaporator coil", air conditioning system filters, and the causes, cures, and prevention of air handler leaks that lead to rust, damage, and mold contamination in the air conditioning system.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Air Handling Unit Blower Fan Speed Adjustment

Photograph of toxic mold growth on a squirrel cage air conditioner blower fan unitThis article describes using jumpers or switch settings or independent controls to adjust the blower fan speed in air handlers used in heating and cooling systems.

There is no single "right" fan speed for all heating and cooling conditions and both high and low speed settings have uses and advantages.

[Click to enlarge any image]

At RETURN AIR, INCREASE we explained that in general,

Higher air speeds are needed during the cooling season than during the heating season.

In general, higher air handler unit (AHU) speeds when running in cooling mode will give quicker cool-down of the occupied space and are suitable during daylight hours when the cooling load will be highest. Higher fan speeds may actdually be more energy-efficient as well. (Khattar un-dated).

Conversely we use a lower fan speed during cooling season to increase the dehumidification or moisture removal in the building, and for night-time operation when the cooling load is reduced. The result is a more-quiet cooling system operation.

Blower Fan Speed Adjustment Options

Fan speeds provided inside the air handler unit may be set or adjusted by

Blower Fan Wire Color Codes

Typical fan wire colors in an air handler or at the blower motor will be (not all of these are always present):

An ohmmeter checking between common (white) and other wires can compare circuit resistance: highest resistance = lowest speed.

Watch out: do not even touch wires or the control board if you are not trained in safe electrical work as you could be shocked or killed.

Be sure to see the wiring diagram on the fan motor and/or on or in the air handler unit itself as well as in the manual.

You've got the manual, right? If not we give a link below for finding manuals for most HVAC equipment.

Read the instructions for your specific air conditioner or heat pump air hander and fan speed control settings as provided by the manufaturer as those will give you actual anticipated air flow rates in CFM (Cubic Feet per Minute) as well as the proper fan speed settings for different conditions or objectives.

Watch out: before changing your blower fan to a higher speed to address air flow that is too weak, make sure that the problem isn't something more basic such as a dirty blower fan, leaky or crushed air ducts, or a dirt or ice-blocked cooling coil or heating coil (for heat pumps).

See those diagnostics

at AIR FLOW TOO WEAK

Question: how do I change the speed on my Rheem air handler?

Rheem electric furnace E30 series fan speed wire positions at InspectApedia.com cited hereinAL said:

Rheem air handler runs too slow when A.C. is on , but runs way fast when furnace is on. wiring must not be correct, am thinking I need to switch 2 wires , am I correct ? and which wires

Reply:

Below we include links for installing and wiring and setting switches on some Rheem air handler units. First let's review a general explanation of how we set the fan speed in HVAC systems.

Most modern heating & cooling air handlers that move air through duct systems for both heating and cooling will have a fan that can run at different speeds or even continuously-variable speed.

Inside the air handler, usually on a control board (a printed circuit board) there will be one or more switches or little jumpers that the service technician can set to control the fan speed or speeds on the particular air handler. It's usually a switch or jumper change, or occasionally on older air handlers, moving a wire from one pin to another.

We need to know the brand and model of your air handler, then to look at the installation and service manual for it (those are available free as PDF downloads here at InspectApedia.com) to see exactly how fan speed is adjusted for your specific machine.

Common air handler fan speeds might be labeled on the circuit board as simply A B C that enables you to move a jumper to connect pairs of pins at each of those locations to select the given fan speed or fan feature.

[Click to enlarge any image]

In the example circuit board diagram shown below, from a York variable speed fan instruction manual (given below) you can see the basics of how jumpers are used to join pairs of pins to set various features provided by the manufacturer.

Photograph of attic air conditioning air handler, condensate drips on floor

On some other air handler circuit boards you may see the fan speed options labeled like this:

And of course on a typical split system heat-pump / cooling unit the remote control will offer additional user control such as a variable fan speed or a very low speed "dehumidification" fan setting.

Low Fan Speed for Dehumidification

Why that very low speed? By slowing the air movement through the cooling coil the system will remove more moisture from humid air than would occur if the blower moves faster because the faster air movement more quickly cools the room down and thus reaches the set temperature on the thermostat. In other words to dehumidify we may need to run the system for a longer time.

See those details at DEHUMIDIFICATION PROBLEMS

In the SPECIFIC INSTRUCTIONS for your air handler you'll see how fan speed should be set: most-often you simply move a jumper between pairs of pins. The instructions will also tell you the actual fan speed in CFM (cubic feet per minute) that your air handler will produce at each setting and the instructions will include a table that guides you in selecting the right fan speed settings.

The schematic I will attach below illustrates fan speed settings for a York Variable Speed air handler NV*S blower.

The instructions for that air handler can be downloaded at inspectapedia.com/aircond/York-Variable-Speed-Air-Handler-Instructions.PDF

Watch out: do NOT try to follow example fan speed setting instructions unless they match your particular brand and model air handler.

Watch out: running the blower speed too fast during air conditioning may result in inadequate dehumidification, while running the fan at too-slow a speed may result in ice blockage on the cooling coil.

Those details are at

FROST BUILD-UP on AIR CONDITIONER COILS

and DEHUMIDIFICATION PROBLEMS

HVAC Blower Fan Installation & Fan Speed Setting Guides

Rheem electric furnace E30 series fan speed wire positions at InspectApedia.com cited herein

Above: with POWER OFF Rheem explains how to change the wire positions to change the blower motor speeds on Rheem E30 series furnaces.

 


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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-02-28 - by (mod) -

@Murray, In addition to measuring noise, you might want to measure air velocity in CFM.

On 2021-02-28 by Murray

I have a geothermal system in my home. The blower has a variable speed ECM motor.. Despite being set to the lowest recommended airflow speed, there is still an excessive amount of air noise from the vents on the floor. Not better with removing the vent cover or changing the filters. Sound measures at 58-62 dB.

I think the unit I have is too big for my home?
Any suggestions for reducing the airflow or airflow noise?
Thanks.

On 2020-09-09 - by (mod) -

Find jumpers or dip switches on the control board

On 2020-09-09 by Rebecca

Change blower speed on a MrCool universal split series that's been converted to downflow? Model MDUI18036

On 2020-06-25 - by (mod) -

Jo

Before prescribing a fix for a noisy air conditioner there are some things we would like to know, in particular exactly what component or components are producing the noise and is the noise normal for those components.

If they technician or installer insists that the equipment is normal and operating correctly and that there are no unusual vibrations are loose connections or motor noises then you might move on to sound isolation steps that we can take. Are we need to answer those questions first

On 2020-06-24 by Jo

I just got a brand new Lenox HVAC system installed. It was very noisy so the installer changed the setting to LOW on the air flow/ fan. It did improve some of the noise factor but will it do any harm to the systems, or take too long to cool or cost more on my electric bill?Is there a better way to eliminate the loud noise?

Thanks for any reply’s or suggestions. I just want this system to function properly.

On 2020-06-06 - by (mod) -

Jarrod

Depending on the brand, model, and age of your air handler the fan speeds are often set by tiny jumpers on a printed circuit board or control board or they may be set by tiny dip switches. Occasionally there are actual wires and need to move among connectors. A service technician can make those changes and adjustments. However be sure to discuss with your service technician why we use different fan speeds for heating vs. Cooling.

On 2020-06-03 by Jarrod


How do I get that changed? Any AC repair place can do this?

On 2020-06-03 - by (mod) -

Jarrod,

It's common for the blower to ve set to change speed between heat and cool modes.

On 2020-06-02 by Jarrod

3 year old furnace and AC unit in my house. The heat works great. When the ac runs, the air is very cold but the airflow out of the registers is less the half then when the heat runs. Is there a setting from the AC unit that is making the air handler blow weaker with the ac or do I have a problem?


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