- Home
- For the homeowner
- Safety
- Definitions
- Gas furnace
- Some error codes for gas furnaces
- Service sheet for the gas furnace
- gas furnace design
- The gas heat exchanger
- Dangerous conditions in gas furnaces
- Annual service of the gas furnace
- Repair procedures for gas furnaces
- Gas fireplace millivolt systems
- Oil furnace
- Setting gas input
- Quick tips for troubleshooting furnaces
- Troubleshoot
- Operation and troubleshoot furnace by manufacturer
- HVAC war stories blog
- Annual service of an oil furnace
- Oil furnace design
- Oil furnace troubleshoot
- Repair procedures for oil furnaces
- Gas code training
- Piping and connections
- FAG w pilot no fire
- Combustion analysis
- Electric furnace
- Air conditioner
- Refrigeration
- Heat Pump
- Boiler
- Ductwork design and troubleshoot
- Thermostats
- Diagnostic problems
- Tools
- Electric test meters
- Electrical diagram training
- Electrical symbols
- Single and 3 phase power systems
- Electric wiring solutions
- Transformer design and troubleshoot
- Electronic air cleaner
- Blowers and fans design & troubleshoot
- Humidity and humidifiers
- Furnace, Air Conditioner and part manuals
- Electric motors
- Run Capacitors
- Start capacitors
- Troubleshooting the capacitor
- Gas furnace short cycling
Blowers and Fans
We use various types of fans to move warm or cold air throughout the structure and to absorb hot or cold air from some sort of heat exchanger. We also use fans to expel hot air from outdoor coils to the outside air.
The above fan on the right is a propellor fan usually used in outdoor units (upper left) to move air across the outdoor coil to pick up heat from the outdoor coil.
The center fan is used in the indoor fan coil unit (usually a furnace) to move air across the indoor coil to cool the air.
The above fan on the right is a propellor fan usually used in outdoor units (upper left) to move air across the outdoor coil to pick up heat from the outdoor coil.
The center fan is used in the indoor fan coil unit (usually a furnace) to move air across the indoor coil to cool the air.
Indoor fan coil unit, furnace, air handler
This is a gas furnace that has a fan for moving air across its heat exchanger. This fan can also be used move air across an air conditioning coil to cool the air.
The indoor fan coil unit, furnace, or air handler generally are terms to describe the same thing.
They all move air throughout the structure by means of ductwork to heat or cool parts of the structure. The video below gives a short narrative on design of the squirrel cage blower.
The indoor fan coil unit, furnace, or air handler generally are terms to describe the same thing.
They all move air throughout the structure by means of ductwork to heat or cool parts of the structure. The video below gives a short narrative on design of the squirrel cage blower.
The 2 videos below demonstrate how the air flow works in the squirrel cage blower. Pay close attention to the amperage draw under the different air flows.
If your blower is a belt drive, the motor pulley may be worn. Worn pulleys may squeal while running or wear out the belt early. If you replace the pulley, the belt must also be replaced. The following video will show you haw to check the pulley for excess wear.
If your indoor blower is belt drive, when replacing a motor or anything that requires moving the pulleys or drive components, the pulleys should be aligned for the most even wear on the pulleys and belt. The video below shows how.
Adjusting the belt on blowers is somewhat different for fractional horsepower blowers than for blowers of 1 or more horsepower. The higher horsepower blowers require tensioning about the same as automotive belts. Approximately 1" depression when pushing on the center of the belt. The fractional hP blower must be considerably less tight. If you tighten them down like the higher hp blowers, the bearings will fail and the motor alignment will be off. The video below demonstrates how to tension.
The outdoor unit.
The propellor fan on the top of this unit draws air through the coil inside the louvres
Removal of fan blades can be a real challenge and some tools and techniques are a big help.
Below is a video about fan blade removal.
Removal of fan blades can be a real challenge and some tools and techniques are a big help.
Below is a video about fan blade removal.
When there is vibration related to the outdoor fan blade, the results can be fairly disastrous. If left unrepaired, it can destroy the motor bearings (resulting in replacement of the motor), the fan can come apart and destroy the outdoor coil and the top cover sheet metal can crack and the fan can drop out. I give some simple ways to do the repair in the video below.
If the fan blades are out of alignment with each other, the fan will vibrate very similar to an out of balance fan blade. The following video shows how to align the blades.
Fan speed control
As long as we have had fans,, we have needed to control their speed. Early fans used belts. Larger units still use belts.
The belt pulleys can be adjusted in size to give the proper speed.
But how do you change the speed while the unit is running?
Obviously, you can't adjust the pulleys while the fan is running unless its a snowmobile.
One way of changing fan speed was to use a choke coil.
A choke coil looks like a low voltage transformer, but may have only 2 or 3 wires.
It is wired in series with the motor.
Because the choke coil is a coil of wire wrapped around an iron core, as the a/c voltage builds, an electromagnetic field is created around the coil of wires. As the cycle moves to zero volts, the magnetic field collapses across the wires. As the field collapses voltage is induced in the wires. This voltage is traveling in the opposite direction as the original voltage. This effectively reduces the voltage of the circuit traveling to the motor. It also reduces the amperage in the circuit. The amount it reduces the voltage is dependent on the number of turns of the coil. Some of these coils may have 3 or 4 taps on the windings to produce different speeds.
This type of speed control is generally no longer used but was actually quite good.
Below is a video demonstrating the use of a choke coil.
The belt pulleys can be adjusted in size to give the proper speed.
But how do you change the speed while the unit is running?
Obviously, you can't adjust the pulleys while the fan is running unless its a snowmobile.
One way of changing fan speed was to use a choke coil.
A choke coil looks like a low voltage transformer, but may have only 2 or 3 wires.
It is wired in series with the motor.
Because the choke coil is a coil of wire wrapped around an iron core, as the a/c voltage builds, an electromagnetic field is created around the coil of wires. As the cycle moves to zero volts, the magnetic field collapses across the wires. As the field collapses voltage is induced in the wires. This voltage is traveling in the opposite direction as the original voltage. This effectively reduces the voltage of the circuit traveling to the motor. It also reduces the amperage in the circuit. The amount it reduces the voltage is dependent on the number of turns of the coil. Some of these coils may have 3 or 4 taps on the windings to produce different speeds.
This type of speed control is generally no longer used but was actually quite good.
Below is a video demonstrating the use of a choke coil.