This section reviews HVAC units, air handling units, exhaust fans, and window A/C units, how they work, routine maintenance, and troubles associated with them.
Operation is based on the principle of using evaporation of a refrigerant to cool the air (see Figure 1).
Figure 1: Basic Air Conditioning Unit
The basic cycle of operation is:
- The compressor (B) compresses the cool, low-pressure refrigerant gas (blue), causing it to become a hot (red), high-pressure refrigerant gas.
- The high-pressure hot gas runs through a coil and dissipates its heat, and then condenses into a liquid.
- The liquid refrigerant goes through an expansion valve (A) and becomes a cold, low-pressure refrigerant gas when it evaporates in the expansion valve.
- This cold gas now runs through a coil that permits the gas to absorb heat, thereby cooling the air inside the building/room.
HVAC refers to heating, ventilation, and air conditioning. This is the means a device or system uses to control the temperature and/or airflow in a room or a building. This can be as simple as a window air conditioning unit to a large system used to supply a building.
A window unit is just an air conditioner small enough to fit into a window and plug it into an electrical outlet (Figure 2). It contains the following elements:
- Expansion valve
- Hot coil
- Cold coil
- Control unit
Figure 2: Typical Window A/C Unit
Maintenance on window A/C units is simply:
- Clean the filters monthly; if it has holes in it, replace it
- Clean the condenser coils annually, and more often if in a dusty environment.
- Do not short cycle the cooling system. When you turn it off, do not turn it on for at least 10 minutes. This allows the pressure inside the system to equalize.
- Check the power to the outlet, fuses, and circuit breakers. If OK, then one of the following may be defective:
- Overload and/or relay
- Selector switch
- Control board
- Selector switch in the wrong setting.
- Thermostat not set correctly.
- Compressor not running.
- Defective condenser.
- Defective evaporator.
- Defective capacitor for compressor motor.
- Check the difference between the air coming in and the air going into the room. There should be at least a 15-degree difference. If there is not, check the air damper. It may be letting in outside air instead of recirculating the room air.
- The winter cover is still on.
- The condenser coils are dirty or clogged. They need to be cleaned regularly to prevent buildup of dirt and loss of efficiency.
- The unit is not cooling properly; see above.
- Thermostat is set too low or not working.
- Unit is sized too small for the space being air-conditioned.
- Drain is plugged or clogged.
- Slinger not working properly.
- Defective overload relay.
- Defective capacitor.
- If it continues, let it rest for approximately 5 minutes, then retry. If problem continues, call an A/C technician.
- Fan motor is defective or electrical circuit to motor is defective.
- Unit is not mounted securely.
- Compressor mounting pads and/or brackets have become worn or broken.
- Unit is not tilted to the rear properly, causing water to collect in the front.
- Remove the unit from its packaging and inspect for damage.
- Use the following cautions when handling the unit:
- Wear gloves, as sheet metal may have sharp edges and will cut.
- Never use the tubing or coils as handgrips to move or lift the unit.
- A/C units are heavy; get assistance when lifting or moving them.
- Open the window, locate the center, and position the base in place.
- Level the base and mark the screw holes.
- Drill mounting holes for the correct screw size.
- Fasten the mounting base to the windowsill using rust-proof screws.
- Adjust the leveling screw until the base tilts downward toward the outside about 1/4 inch.
Figure 3: Installing Mounting Unit
- Slide the unit into the mounting base, but do not force it in. Recheck that the mounting base is level and square.
- Install spacers between each side of the unit and the frame of the window.
- Install rubber gaskets along the top of the unit.
- Install a gasket between the upper and lower portions of the double-hung window.
- Install a double-hung sash lock.
- Use a sealer to fill in all cracks around the unit that will let air/water seep inside.
Figure 4: Installation of Filler Panel Between Housing and Window
- The unit should be connected to an outlet on its own circuit.
- The plug for the unit should be polarized with a ground.
- Make a final visual inspection and then start the unit.
- If it does not start, check items in the Typical Problems list.
- When the unit is running, check for leaks inside the conditioned space. If it is leaking, adjust the tilt of the unit.
- Check for excessive noise and vibration and adjust as necessary.
- Adjust the cutout to between 56 and 60F and the cut-in to between 77 and 80F.