Air Purification Products
Honeywell® Thermostats
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James A/C Co.
serving Do-It-Yourselfers since 1990.
Satisfying every customer....one at a time!
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Call toll free 1-866-584-0355 or 1-903-759-2160
309 Patriot Circle, Longview, TX 75604-2240
THINGS TO CHECK IF THE INDOOR FAN WON'T START OR MAKES NOISE:
Most of the following items for the blower motor and related parts will apply to other motors (like the condenser motor) as well.
The most common cause of the motor failures is dirt. This is caused by a lack of GOOD FILTRATION. Dirt works its way into the
bearings and eats them up and the dirt restricts the cooling of the motor by ventilation and the windings short or burn in two.
When checking the blower motor you SHOULD NOT have the thermostat set in the
cooling or heating position. It could come on automatically and injure you. Additionally, you will probably have to turn the unit on
and off several times and you surely do not want to do
that to the outside compressor. Set the system switch to OFF and the fan switch can be alternated from the "auto" to the "on"
position when testing the blower motor reactions.
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- Bearings or bushing bad in the motor will cause a motor to pick up speed more slowly
and the movement of it is accompanied by a growling type sound. The bushing has worn to an egg shape or the bearing has developed
a bad area. Usually, the wear is at the bottom of the bearing or bushing where the gravity has been holding the internal shaft
down on it. When the motor does get up to speed it may still have some of that low growl as it runs. The speed will likely be
reduced in rpm (revolutions per minute) but will be difficult for you to detect.
If the motor will not start at all, turn it on and carefully spin the blower wheel in the correct direction. It it now runs,
the bearings are likely worn badly. When a motor has reached this state, it is usually too late to save it. There are
several options:
- Oil the motor very well and see if it will temporarily get you by until a better time to repair or replace it.
If you can feel movement of the shaft perpendicular to the motor, then you know the bearing is not perfectly round.
Don't worry about the motor shaft movement in and out of the motor. That is called "end-play" and it is normal.
- TIP--Remove the blower assembly and rotate the mounting position of the motor 90°.
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The purpose of this action is to let gravity lay the shaft (inside the motor) on a good surface of the egg-shaped
bushing or to a better location of a bearing. If you once get it running it might be best to set the thermostat so that the fan
runs continuously and thus it will not have to try to restart. To do that, set the FAN switch to the ON position. This doesn't
have any effect on the compressor cycling. Oil it really well before you set it to run and listen to notice that is will be okay. |
This is a very temporary cure for a terminal problem.
- Remove the motor and let a motor repair shop install new bearings.
- Remove the motor and replace it with an identical one or suitable replacement. If you change the motor, be sure to
check the size of the capacitor needed and change it also if necessary.
- Foreign objects. Make sure no objects have lodged inside the blower wheel and
is preventing it from moving. ANY FOREIGN objects in the blower wheel will cause some vibration. An object the size
of a 2 x 2 inches piece of paper will cause violent vibration and some serious wear on the motor bearings. This needs
an immediate solution.
- If it is belt driven, make certain the belt or the bearing on the blower wheel in
not the problem. Remove the belt and spin the blower and listen for rubbing or growling sounds or check for resistance
to movement. Check the pulley or sheave on the motor and the blower wheel shaft to verify they are okay. Check the
alignment of the belt from one pulley to the trough of the other. Check the tightness of the tension of the belt:
- The blower door safety switch can be the cause if nothing at all runs.
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It cuts the incoming power off to the unit, so nothing will even click or try to run. The first way to
check it is to make sure the blower door is in place properly. You must have it in place according to the original manufacturers
design or it may not work. If the switch is broken, then you can get a replacement at the dealer or you can temporarily just remove
the two wires on it and tie them together, thus by-passing the switch. This switch is important and do not leave it by-passed for a
long period of time. It is there for your safety. |
- Low Voltage fuse. Your system is probably operated by a low voltage circuit with the low
voltage supplied by a transformer inside the heater (furnace or air handler).
Many low voltage circuits have fuses that may have burned. Always replace it with an identical size and try to locate a fault in
the circuit that caused the problem. Some of the typical causes my be shorted contactor coils, shorted control wires, grounded
wires and/or low voltage wires shorted to high voltage wires, obstruction of the movement of the contactor contact points or
slide mechanism.
- Low voltage wiring. Dogs, hedge trimmers and weed trimmers are sometimes the cause of the
low voltage control wires being shorted between the outside walls and the condensing units. Occasionally, gardening or utility
repairs will cut the wires in the ground. Even a momentary short of these wires may burn a fuse or transformer and everything shuts
down.
- Rodents, etc. will sometimes gnaw at the wire and insulation as it enters the slab or building
structure and also as it enters the floor of homes on the way to the indoor unit. If these rodents, etc. have made their way into
the house, then suspect cut or broken wires at any place where they may have traveled. They seem to like rubber and plastic products.
- The fan relay could be NOT sending voltage to the motor. Before you attempt to check it,
make sure the supply voltage is in the unit properly and the low voltage is present for the control circuits.
A fan relay is merely a contact that closes to allow voltage to proceed on to the motor when you need it and will be just an open
circuit when the motor is not wanted.
Fan relays come in many shapes and sizes. Some are built into the printed circuit board (PCB) and will be more difficult to
diagnose (like item 6 in the drawing below). If the relay is in a PCB and is faulty, then the whole PCB will have to be replaced.
Many are independent and remote components and should be fairly easy to locate. Follow the wires from the motor back to the control
panel and/or to near the incoming power and at least one of the wires will be attached to a fan relay.
A relay will need low voltage to make it close, so check to see if the low voltage is working. A good way to determine this is the
turn the fan switch on the thermostat to the ON position and listen for the low voltage to make the fan relay CLICK. With the
exception of the PCB mounted relays, if you don't have a click it means you probably have no low voltage.
One of the very best ways to determine if the relay is working is to find some location in the wiring going to and near the motor
where you can check the voltage. If you have the correct voltage to the motor, then the relay is working. But you need to know
which wires to check for correct voltage:
- A motor requires two wire leads to make it run, but most blower motors have more than two wires
- One wire will be a common lead that probably goes directly to a voltage source without controls or interruption.
Likely colors for this lead are white, yellow, purple or orange. This will be one of the leads you need to use to check the
voltage to the motor.
- Two of the leads may go to a capacitor. These are usually brown in color. You won't connect to them to check the
voltage.
- This leaves us one to four other wires to define. The number of wires remaining determines the number of speed taps
the motor has available to use. Odds are good they will be black, blue, red and possibly an orange one. Each one, if
used, will make the motor run at a predetermined speed. You may notice that some of them are not used and are taped-off
or lead to a blank terminal (thus are not used).
- BLACK may be the color for the highest speed.
- BLUE may be the color for the medium or medium high speed. This might be the orange wire, though. Different
manufacturers choose to use the color they like.
- RED may be the color of the lowest speed.
- So you will connect one test lead of the voltage meter to the common wire and the other test lead to one of these speed taps
of the motor. Most often the high speed is used in cooling or in constant fan operation. Alternately it will be one speed lower,
depending on the requirements. A much lower speed will be used in the heating operation unless it is a heat pump, in which case
it will be in one of the highest speeds as is cooling.
Your meter should show a reading from the common wire to the high speed of anywhere from 2 ohms to 40 or 50, depending on the motor
and the design specifications. Check each of the speed selection wires to common and each lower speed will read more resistance
progressively down to the lowest speed. Likely, your readings will be from 2 to 15 ohms in range with the 2 being the high speed
wire measured to the common.
- Most motors will be 120 VAC or 240 VAC. Gas heaters usually have 120 VAC to them and electric heat units usually have 240 VAC.
Check the unit name plate to be sure.
- Motor capacitor open or shorted. This, of course is the capacitor that works with the blower
motor. In the picture of the blower assembly at the top of this page the number 53 is the capacitor
for that particular motor.
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The number 5 here is the capacitor and is shown mounted on a control panel with a transformer and the printed circuit board
fan controller. You will likely see bulging of the physical shape of a bad capacitor of the older types or oil may be leaking
from it. Otherwise, you will just have to take the capacitor to a dealer and let him check it and supply you with a new one
if it checks bad. Notice that this one is cylindrical in shape. |
You are not apt to have the proper meter to check this for yourself.
One thing you can check if you have a VOLT-OHM METER or continuity checker is to remove the wires from the capacitor and see if it
is shorted between the two posts on the capacitor. You should register no circuit of low ohm resistance.
If the meter will check MEGA-OHMS, you can check the terminals and the needle will jump upward and instantly fall back to zero.
Reverse the leads of the meter and check it again. You will notice the same jump of the meter, but it will likely be higher up
the scale and again fall back less quickly to zero. This will likely mean the capacitor is good. This check is for a shorted
capacitor only, not a measurement of its capacitance, but is fairly accurate in pointing out a bad capacitor.
- Shorted motor windings or windings grounded to the frame of the motor will create varied symptoms
of motor failure. Use caution before you touch any unit having difficulty. Carefully make sure the blower housing is not standing full
of water from condensation water (if the coil is above it). It may be shorting the electrical fields of the motor. Before you grab hold
of anything, touch the BACK of your finger to the equipment and see if there is any sign of electrical tingle from it. If there is any
doubt of safety, unplug or disconnect the voltage to the device before you attempt to work on it.
¹ Logos and pictures Copyright © 1999 Honeywell Inc. All rights reserved
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If you have
comments or suggestions, please email me at James' A/C Co.
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