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How-To Wire Condenser Fan Motors Properly in 3-Wire & 4-Wire Configurations

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“My original condenser fan motor has three wires and the replacement condenser fan motor that I bought has four wires – did I buy the wrong motor?”

This is by far the most common post-transaction question that we receive from customers that have recently purchased replacement condenser fan motors. Simply put, no – you did not buy the wrong condenser fan motor. While most original condenser fan motors only have three wires, it’s very common for replacement condenser fan motors to have four. This guide will explain how to wire your new condenser fan motor using a four wire setup or a three wire setup when using a single run capacitor or a dual run capacitor.

A review of the components:

If you recall from our residential cooling season guide, outdoor condenser units use a switch called a contactor. This switch is controlled by the thermostat and closes to complete an electrical circuit when electricity needs to be supplied to your condenser fan motor and compressor. Think of the contactor almost as a gatekeeper – two legs of 115 volt electric supply need to flow through it in order for your system to function properly.

Condenser units also use a component called a run capacitor. Run capacitors allow condenser fan motors and compressors to run more efficiently and they’re rated by a unit of measurement called microfarad. Dual run capacitors are used for both your condenser fan motor and your compressor. Single run capacitors are used exclusively for just your condenser fan motor or just your compressor. Like your contactor, your capacitor needs to be wired correctly in order for it to function properly.

Run and Start Capacitors

 

Using a dual run capacitor:

If you’re using a dual run capacitor, you’re only going to use three of the four leads coming off the new condenser fan motor.

You’re going to wire the black lead to where the black lead on your previous condenser fan motor was wired to. This will likely be back to your contactor. You’re going to wire the white lead to where the white lead on your previous condenser fan motor was wired to. This will likely be the “C” or “Common” terminal on your dual run capacitor. Finally, you’re going to wire the brown lead to where your previous brown lead was wired to. This will likely be the “F” or “Fan” terminal on your dual run capacitor. The brown lead with the white tracer will not be used for this setup. You can use a wire nut and electrical tape to tie it off.

NOTE: You’ll need a jumper between the “C” or “Common” terminal on the capacitor and one leg of the contactor.

Using a single run capacitor with a four wire setup:

If you purchased a new condenser fan motor with a new single run capacitor, this will be the wiring setup that you’ll be using. You’re going to wire the black lead to where the black lead on your previous condenser fan motor was wired to. This will likely be back to your contactor. You’re going to wire the white lead back to the other leg of your contactor. You’re going to wire the brown lead to one set of terminals on your new capacitor and you’re going to wire the brown lead with the white tracer to the other set of terminals.

Using a single run capacitor with a three wire setup:

If you purchased a new single run capacitor and the condenser fan motor that you’re using only has three leads coming off of it, this will be the wiring setup that you’ll be using. You’re going to wire the black lead back to where it was previously wired. This will likely be back to your contactor. You’re going to wire the white lead to one set of terminals on your new capacitor. You’re going to need to wire a jumper from this set of terminals back to the other leg on your contactor. Finally, you’re going to wire the brown lead to the opposite set of terminals on your new run capacitor than the common lead.

Sum it all up:

There’s always a sense of fulfillment when completing a project yourself, but wiring a new condenser fan motor and run capacitor can be a bit tricky if you haven’t done it before. Safety is always the highest priority. Make sure the electrical supply to the condenser unit is disconnected before beginning any work. Use your multimeter to confirm the disconnection. If you’re not comfortable working with electricity, contact a local HVAC contractor and they will be more than happy to complete this task for you.

It’s very helpful to document the location of existing wire connections before removing the condenser fan motor or run capacitor. Use a camera to take pictures of the connections and reference the pictures when installing the new condenser fan motor and run capacitor.

For a visual picture of typical wiring configurations, reference the following guide: HVAC Condenser Fan Motor Wiring Diagram.

Finally, this guide is intended to be used as a general overview of common condenser unit wiring schematics. Some condenser fan motors wire to a circuit board while others use proprietary plugs for their connectors. We strongly recommend referring back to your unit’s manual for proper wiring instructions.

Let us Find Your Condenser Motor or Capacitor for You

 

How-To Get those AC’s Bumping with Ice-Cold Air Before the Heat Overwhelms Your Home

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The thermometer reached 75 this past weekend in Chicago, which means we’re officially entering cooling season. Cooling season is the industry term for when we use our air conditioning units – compared to heating season for when we use our furnaces.

Most people cross their fingers when turning on their air conditioners for the first of the year and they hope everything will function properly. That’s not really the best approach. This guide can be used as a high level overview of the residential HVAC system components used during cooling season and how to troubleshoot some problems that might arise.

The two main components of your residential HVAC cooling system that we’ll focus on in this guide are the indoor air handler and the outdoor condenser unit. Both need to be functioning properly in order for your house to stay cooled and comfortable.

Let’s start with your indoor air handler.

Mounted inside most residential air handlers is a direct drive blower motor. This is the motor that circulates cooled air in the summer, and warmed air in the winter, throughout your house. To move air, a blower wheel – sometimes called a squirrel cage – is secured directly onto the shaft of the blower motor using a set screw.

Some OEM blower motors have 3 or 4 legs welded to the side of the motor that are used to mount the motor to the blower housing. This mounting style is called the torsion flex mount. There are torsion flex mount replacement blower motors available, but they’re usually much more expensive than traditional blower motors.

It’s good practice to replace your run capacitor when replacing your motor and it’s important to note that the correct run capacitor is chosen by the requirements of each specific motor. You might be replacing a ½ HP blower motor that requires a 7.5 microfarad capacitor with a ½ HP motor that requires a 10 microfarad capacitor. Avoid the headache by replacing the run capacitor when replacing the motor.

Now, let’s take a look at your outdoor condenser unit.

Your outdoor condenser unit is the heart of your central air conditioning system. Without getting too far lost in the weeds of thermodynamic principles, refrigerant is circulating through the system’s coils where it transitions from hot to cold, gas to liquid depending on where in the line it is at. To help cool the very hot gases after they pass through the compressor, a condenser fan motor is used to pull air from outside of the unit over the unit’s coils and out the top of the condenser unit.

Most residential air conditioning units use a thermostat as a control to turn the system on and off as the room’s temperature fluctuates in and out of a defined temperature range. When it’s time to supply power to the condenser unit, the thermostat sends a signal to a switch called a contactor – which closes the circuit and supplies electricity to the compressor and the condenser fan motor.

Residential condenser fan motors are most commonly mounted to the top screen of the condenser unit with the motor’s shaft pointing down. Other condenser units require the condenser fan motor to be mounted with the shaft up or even horizontally. While many condenser fan motors are totally enclosed and rated for all angle mount, others are open ventilated and manufactured for a specific mounting direction. It’s important to select a motor that is rated for the corrected orientation of your condenser unit.

The condenser fan blade is mounted to the condenser fan motor shaft using an interchangeable hub. The proper hub is selected by considering the fan motor’s shaft diameter. Most residential condenser fan motors are 48 frame motors with a 1/2″ diameter shaft and many commercial condenser fan motors are 56 frame motors with 5/8″ diameter shaft.

When replacing a condenser fan blade, it’s important to select one that is properly rated for your condenser unit and your condenser fan motor. We use a formula that considers the diameter of your existing fan blade, the HP rating of your new condenser fan motor and the motor’s RPM rating. Selecting an improper condenser fan blade can cause your system to not function properly, so it’s important to double check your work and make sure that you’re using the proper replacement condenser fan blade. Refer to our Condenser Fan Blade Replacement Guide for more information.

Tips and Solutions for Common Problems

Problem: Your blower motor is very squeaky.

Solution: Most direct drive blower wheels have sleeve bearings which need to be maintained. For sleeve bearing motors, it is recommended to lubricate the bearings with a few drops of twenty weight non-detergent at the start of each heating and cooling season.

Problem: The blower motor shaft is completely locked up.

Solution: If your blower motor’s bearings have completely failed and the shaft is locked up, the motor will need to be replaced. Bearings often fail because the fan blade, or blower wheel, that the motor is driving isn’t balanced properly – which causes the shaft to rotate in an oval pattern and not a circular pattern. This puts added stress on the poles of the bearings which leads to their failure. If your blower motor’s bearings are looked up, it is highly recommended to replace the blower wheel when replacing the blower motor.

Problem: Your motor is having a hard time starting or simply won’t start.

Solution: If your motor is having a hard time starting or seems sluggish, you’ll want to check the motor’s run capacitor. Use a multimeter in capacitance mode to get a microfarad reading from the run capacitor. If the microfarad reading is in line with capacitor’s rating, then the capacitor is good. If the microfarad reading is significantly lower, then the capacitor is bad and will need to be replaced.

Problem: The condenser fan motor doesn’t run or the air conditioning system isn’t cooling properly.

Solution: As with the direct drive blower motor, if the condenser fan motor doesn’t start or the system doesn’t seem to cool properly, the first item that you’re going to want to check is the unit’s dual run capacitor. A dual run capacitor is rated for both your condenser fan motor and also your compressor, so you’ll have to pay close attention to make sure any replacement is rated properly for both items.

Tip: To save money when replacing a blower motor – buy a standard blower motor with a belly band. Belly bands create the mounting set-up identical to a torsion flex mount motor and are a fraction of the cost.

Tip: Set screws often require the use of an Allen or Torx wrench – so it’s wise to have one available.

Replacement Parts for your Air Handler

Replacement Parts for your Condenser Unit

How-To: Tackle Condenser Fan Blade Replacement

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When replacing a condenser fan motor, it’s always advised to replace the condenser fan blade also. Here’s the reason why – condenser fan motors commonly fail when their bearings fail. The motor’s bearings often fail when the fan blade the motor is driving isn’t balanced properly. By replacing the condenser fan blade when you replace your condenser fan motor, you can rest assure that the fan blade is balanced properly and will rotate in a perfect circle.

Replacing a condenser fan blade is fairly straightforward. The four items that you’re going to need to take into consideration are the direction of airflow, the diameter of the fan blade, the motor’s HP and the motor’s RPM rating. By using these four items, you can have confidence in knowing that you selected the proper replacement condenser fan blade for your new condenser fan motor.

Determining the direction of airflow for the condenser fan blade.

When moving air with a fan blade, you either push it forward or your pull it back over the motor. To push air forward, you need to match the rotation of the fan blade with the rotation of the fan motor. A CW motor paired with a CW fan blade will push air forward – as will a CCW motor paired with a CCW fan blade. To pull air back over the motor, you select the opposite rotation on the fan blade to the rotation of the fan motor. A CCW motor paired with a CW fan blade will pull air backwards – as will a CW motor paired with a CCW fan blade. It’s important to note that shaft rotations are given from shaft end orientation.

Measuring the radius of your condenser fan blade.

The next step is measure the radius of your existing condenser fan blade. While fan blades are rated by diameter, best practice is to measure the radius by starting at the center of the condenser fan blade and measuring out to the outer tip. Simply take the radius and multiply it by two to give you the diameter.

Finding the motor’s HP and RPM rating.

To find the HP and RPM rating of your new motor, simply look at the motor’s nameplate specifications. Almost all motors have this information printed onto a sticker that’s attached to the side of the motor.

Final steps of finding the correct condenser fan blade.

To put all of these things together and select the right fan blade – you’re going to use Lau’s chart on propeller performance of heavy duty condenser fan blades. First, find the section of the chart that has your diameter. Next, turn your motor’s fractional HP into a decimal and match it with the proper RPM without going over the listed HP (see example below). Finally, select the proper rotation based on your desired direction of airflow. Click the part number and you’re done.

Don’t forget the interchangable hub!

Example scenario of a condenser fan blade replacement:

You have a 1/10 HP motor with an 825 RPM rating and you’re looking for an 18” diameter condenser fan blade. Turn 1/10 HP into a decimal to get 0.10 HP. Browse the 18” diameter fan blades and look at the HP ratings for 825 RPM. Notice that the 23 degree pitch blade is rated for 0.103YOU’RE Your 0.10 HP motor comes in right under the 0.103 HP, so this would be the proper replacement blade for a 1/10 HP motor at 825 RPM.