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How to hook up an electric motor start or run capacitor:
This article gives electric motor start-run capacitor installation & wiring instructions for electric motor capacitors designed to start & run an electric motor such as an AC compressor, heat pump compressor or a fan motor, and how to wire up a hard-starting air conditioner compressor motor, fan motor, to get an air conditioner, heat pump, refrigerator, or freezer compressor or other electric motor (such as a well pump) going.
This electric motor capacitor article series explains the selection, installation, testing, & use of electric motor starter start and run capacitors used on various electric motors found in or at buildings such as air conditioner compressors, fan motors, some well pumps and some heating equipment.
Most electrical problems in air conditioning systems are in the compressors and their relays or motor overload switches.
In a single phase (common residential A/C) compressor you can verify with an ohmmeter whether or not the A/C compressor is bad.
[Click to enlarge the image at left]
Watch out: live high voltage may be present at a capacitor, capable of giving a tremendous electrical shock even after electrical power has been disconnected at the equipment. Never work on live electrical equipment.
Also see STARTING CAPACITOR SAFETY
A fractional horsepower electrical motor should show different electrical resistance between the three terminals (Start, Run, and Common) as we illustrate just below.
Find the two highest resistance terminals.
The third one will be the common terminal.
Our example is for a Frigidaire compressor motor.
In our capacitor testing and wiring sketch at left, you note we use the letters S, C, and R to identify the usual terminals to which a start/run capacitor is wired. On many systems these terminals may be labeled so that the three leads on a start/run capacitor can be wired correctly:
Electric Motor run speed side note: Incidentally while most electric motors are marked with a data tag indicating the motor run speed (in RPMs) it's worth noting that the number of run coils is what determines the run speed of the motor. Two-coils marks a motor that runs at 3450 rpm (3600 rpm "nominal"), while 4 coils marks a 1725 rpm motor. (120V, 60 cycle/sec x 60 sec/min = 3600 rpm).
Electric motor diagnostic procedures are given in detail
at ELECTRIC MOTOR DIAGNOSTIC GUIDE
Relay and hard start capacitors such as the Starter Pow-R-Pak sold by Sealed Unit Parts Co., can be installed with no wiring changes to the original system whatsoever. Quoting from Part No. SPP-5, a relay and hard start capacitor sold by that company:
Connect the two wires from the SPP-5 in parallel with the [existing, already installed] run capacitor (one wire each side) without removing any original wires.
Use special "piggy back" terminal of the SPP-5 if all the run capacitor terminals are being used. [Install only on PSC units equipped with run capacitor.]
Here are some sample capacitor installation instructions for adding a motor starter capacitor to an air conditioning compressor motor - taken from the product package for a relay and start capacitor intended for use on a refrigerator or freezer. Similar starter capacitors are available for air conditioning compressors.
[Click to enlarge any image]
Start/run electric motor capacitors can be mounted in any direction or position. However there are some other capacitor mounting considerations that can affect capacitor life: basically you want to minimize the capacitor's exposure to vibration and heat.
As Afacp points out, ..."the temperature on the surface of the capacitor cannot exceed, even under the worst conditions, the maximum permitted temperature.
It is advisable to make an experimental measurement of the temperature reached by the capacitor under the working conditions in the final application and after the thermal equilibrium has been achieved."
When testing a compressor, one must discharge the capacitor first! It'll otherwise have enough power stored on it to be at least very painful. (Author and others have been zapped!)
Some systems will automatically discharge the capacitor, but shorting its leads [to ground] with a screwdriver (after verifying that the power's off) is a safe way to ensure that you won't get shocked. Motor starting capacitors can hold a charge for days!
If oil has leaked out of a capacitor: Don't touch any oil that leaked out: old capacitors may contain PCB oils, an extremely carcinogenic (cancer causing) material which require special disposal.
Once the capacitor has been discharged (as described just above), then it can be tested with a multi meter. Either use the meter's built in capacitor test function, or use this trick: Charge the capacitor by using the sense current the meter puts out when set to ohms. You should observe a rapidly rising resistance before the meter indicates over range/infinity.
Disconnect the test leads, and switch over to volts. Then, reconnect the test leads. A voltage reading should be observed, approaching zero.
If the capacitor doesn't hold a charge, or the resistance reading never approaches infinity, it probably needs replacement.
Also, the capacitor may be defective if the compressor hums but does not start. Visual inspection may reveal it to be bulged, or have a blown out safety plug.
On 2017-07-09 by Brian Render
I'm replacing my run capacitor in my air handler. I forgot to mark the wires I took off. I have 4 wires. A blue, a black, a yellow, and a brown. Brown , and yellow come from the motor. Red, and black go to a control box. What goes where?
On 2017-07-09 by (mod) Typical color codes & wiring connections for an air handler blower fan or a compressor/condenser fan & compressor wires
RE: wiring up an HVAC air handler fan motor capacitor:
You reported four but listed five wirres in your air handler and that were connected to the run capacitor:
BLACK - to a control box
YELLOW - from motor
BROWN - from motor
RED - to a control box - typically wires to C
The reason you can spend hours looking at online chats about HVAC start-run capacitor wiring without finding a single absolutely-right guide to capacitor wiring color codes is that the service techs who make these repairs don’t want to give an answer that kills someone or burns up their equipment.
Watch out: touching live voltage can kill you. Turn power off and discharge any capacitors before touching anything. A capacitor can store a charge that can hurt you or worse even after power has been turned off. If you’re not sufficiently trained and informed about electrical repairs hire someone who can do the work properly and safely.
The tech will typically use an insulated screwdriver to short the F or H terminals to the COM terminal to discharge the cap.
While there are common capacitor wiring color conventions that I will cite below, the actually-correct wire colour match to fan motor terminals, wires, and capacitor terminals may vary by motor brand, age, model and application. But there are steps that can help sort out which wires go where.
Next time, remember to tag each wire with an ID and write down its connections before removing wires from their connections on electrical equipment.
Watch out: It's safest to take a look at the wiring diagram on the equipment itself - you can follow them to the marked-terminals on your start or run capacitor. There are also some simple VOM tests that can help identify motor terminals.
Look at the wiring diagram for your specific HVAC equipment and find the capacitor where you’ll see its wires and their identities. You should see a wiring diagram glued to the inside of the air handler cabinet or to the inside of the blower compartment door.
You can also obtain a wiring diagram for your air handler brand, model, serial number from the manufacturer, or give us that information and we’ll help dig it out.
Now with all that scary arm waving done:
HVAC service technicians are invited to CONTACT us to improve these general color codes & wiring tips for start/run capacitors, dual capacitors, and fan or compressor motors. We are happy to cite, credit, and refer readers to expert sources & technical content contributors.
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Blower fan motors and other fan motors may have what look like extra wires, not all of which may be in use, depending on the fan speeds required.
Usually the following wire colors will connect to the terminals or sources or controls we list below - you’ll see data like this (though the colors may be different) on the wiring diagram for your own equipment.
Watch out: Your equipment’s wiring diagram and what its manufacturer tells you will be the final authority on which connections are correct.
HVAC Capacitor Wiring Color Codes & Connections - Basics
|Wire Color||Typical Connections
Blower Assembly / Fan
Power source. Usually connects to C or Common terminal on the Capacitor.
Compressor contactor relay T1 to C on the Compressor motor terminal
Black also wires from Compressor Contactor T1 to T5 on Start Relay
Air handler unit blower fan motor to T1 terminal on contactor relay
Power from a fan relay to the fan motor
|Red - power source||
Power source. Usually connects to R or Run terminal on the Capacitor.
Compressor contactor relay T2 to R on the Compressor motor terminal
Power from fan relay to fan motor will typically connect to the T2 terminal on the Contactor relay.
For multi-speed fans red = low speed motor terminal
Two blue low voltage wires to operate the contactor relay magnet
Often: Compressor R or Run terminal to S on the Compressor Start capacitor
|Power for medium speed motor terminal|
Fan motor to capacitor (motor start terminal)
Connects fan to the F or FAN terminal on the capacitor to fan motor
Fan motor to the capacitor (from the motor start terminal)
Connects the Fan motor to the F or FAN terminal on the capacitor for the fan motor
|Brown + White||
Same use as white wire, C on capacitor to T2 on contactor
Not used when using a dual start/run cap
Same use as white wire, C (common) on capacitor to T2 on contactor
Not used when using a dual start/run cap
|Green||Ground wire in nearly all systems|
From power terminal on fan motor to C or COM on the capacitor
Outdoor Fan Motor to C or COM or RC connector on the Run or Start/Run Capacitor
|For multi-speed fans, orange is medium-low speed|
S terminal on Compressor to HERM or H on the Run or Start/Run Capacitor
May be ground or neutral.
Fan motor direction reverse to counterclockwise if grounded - connect purple to yellow to reverse.
Connect from fan to the COM terminal on the capacitor
Compressor contactor relay T2 to R on the Compressor
Start Relay T1 to C on a separate Start Capacitor
Compressor to the H or HERM terminal on the capacitor
Often: Compressor Start Relay to C on the Compressor Start Capacitor
|From a fan motor controls the medium speed motor|
|White||Common wires connect to the grounded (neutral ) side of power source||Common wires connect to the grounded (neutral ) side of power source|
Electric motor speed taps: typical: L2 connects to
Black = high speed
Blue = medium speed
Red = low speed
Purple to purple = rotate clockwise
Purple to yellow = rotate counter-clockwise
Dayton Electric Motor Wiring Diagram [PDF], Dayton Electric Mfg. Co., 5959 W. Howard St., Niles IL 60714 USA, retrieved 2017/07/09, original source: Grainger.com
Continue reading at EXAMPLE of CAPACITOR REPLACEMENT or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see MOTOR CAPACITOR TYPES for photos identifying the terminals on start and run capacitors and indicating which wires are connected to which terminals.
Also see STARTING CAPACITOR SAFETY
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Questions & answers on the wiring connections for electric motor start / run capacitor wiring as is typically found on heating & air conditioning systems as well as on other electric motors such as well pumps, sewage pumps, and electric shop tools posted originally at this article are now found at MOTOR CAPACITOR WIRING FAQs
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The SUPCO E-Class Series comprise the most advanced developments in start device technology:
1. Voltage sensing technology that monitors for motor start (current sensing devices require internal fuse protection).
2. A 2-wire connection that simplifies installation
3. A secondary timing circuit that ensures that the capacitor is not permanently left in the start winding circuit
4. A fully electronic device - minimizing the limitations of mechanical devices and secondary fusing associated with triac devices
5. A start device matched with an appropriately sized capacitor to cover the range of compressors for the intended application (one size does not fit all)
The use of compressor start devices results from a need to ensure that a compressor (usually air conditioning) will start under voltage conditions that are less than ideal. As discussed, several options exist in the market to address compressor start concerns. Start devices exist in many forms for specific applications. SUPCO provides a full range of products in all relevant technologies to effectively match the proper start device to the application. Care should be taken to utilize a device that meets the requirements of the job. Extra caution should be observed when employing the "one-size-fits-all" and "a bigger capacitor is better" approach to applying a start device. Consult SUPCO, a manufacturer with a complete product range, to ensure the greatest success in the start device application.