How do heat pumps and cooling systems differ?
An AC unit only pumps heat in one direction. A heat pump can pump heat in two directions. It can send heat to a space where it can be used to condition it.
Briefly describe how a four way valve allows a heat pump to change modes.
It is a device that allows a heat pump to switch between heating and cooling modes. It can send heat to one coil for cooling mode (outdoor coil) or to the other coil for heating mode (indoor coil).
In the heating mode, which coil acts as the condenser and which coil acts the evaporator?
The indoor coil acts as the condenser and the outdoor coil acts as the evaporator.
What does "air to air" mean?
It describes which medium is the source of heat and which medium is being treated. In this case, the heat pump is removing heat from the inside or outside air and depositing it in the other inside or outside air.
How does a four way valve work?
The valve diverts the discharge gas and heat to the proper direction. It has a slide mechanism in it. The position of the slide is determined by a solenoid that is energized for one mode and de-energized for the other.
What is the typical mode when the solenoid is not energized and energized?
Typically it is not energized when in heating mode and energized when in cooling mode.
Describe what the four lines of the valve are connected to.
The single line coming from the top of the valve is the discharge line from compressor.
The center line on the bottom is always the suction line to compressor/accumulator.
One of the side lines is connected to the outdoor coil and the other side line is c
What is a direct acting solenoid?
It is a solenoid that itself is providing the force needed to change the position of the slide in the valve. This solenoid is usually found on smaller heat pump systems.
What is pilot-operated reversing valve?
It is a valve that uses the pressures in the heat pump system to help move the slide in the valve. The valve movement is controlled by pressure differences on piston within the valve. Small piping that runs along the side of the valve is connected to the
How do you remove a four way valve?
Use a special torch tip that can heat all three tubes at the same time and on both sides. Make sure to cover the valve body with wet rags or heat sink paste to protect the valve from damage.
How can a valve be damaged if it is not covered with wet rags?
There is a small nylon pad that the piston slides on. If it gets too hot, it will melt and not function.
What is a gas line, a liquid line and how do you identify them?
The gas line carries the vapor or gas. It is the largest of the two lines. The liquid line carries the liquid refrigerant and is the small of the two lines.
How are heat pump metering devices different from regular AC systems?
There must be a metering device at the indoor unit as well as the outdoor unit.
When using a TXV, what other device must be used with it and why?
A check valve is needed to be piped in parallel with the TXV to allow flow around the TXV when in the other mode.
Are heat pump TXVs and regular AC system TXVs interchangeable?
No, the gas line on a heat pump may become too hot for a typical TXV sensing bulb.
Which coil has a larger bore for an orifice metering device?
The indoor coil has a larger bore than the outdoor coil because the summer cycle uses more refrigerant in normal operation.
What is a biflow filter drier?
It is a liquid line filter drier that allow flow in either direction. It is actually two driers in one shell with check valves in the shell to cause the liquid to flow in the proper direction at the proper time.
Where are air to air heat pumps usually installed?
They need to be installed in milder climates where the coldest temperature does not go below 10�F.
What is auxiliary heat?
Heat pumps may not have enough capacity to fully heat a home when the temperatures drop. It needs help in the form of auxiliary heat. Usually it is in form of electric, gas or oil with electric the most popular. Auxiliary heat makes up the difference in t
What is the balance point?
It is the point when the heat pump can pump in exactly as much heat as the structure is leaking out. At this point, the heat pump will completely heat the structure by running continuously. Above this point, it will cycle on and off. Below this point, it
What is the coefficient of performance for electric heat and heat pumps?
For electric heat, the COP is 1:1. For heat pumps, it is 3.5:1. Thus a heat pump is 350% more efficient than electric heat.
For a split system heat pump, where must the auxiliary heating coil be located in relation to the refrigerant coil?
The refrigerant coil must be located in the air stream before the auxiliary heating coil. If the heating coil is located before the refrigerant coil, the head pressure will be too high and may rupture the coil.
What is emergency heat?
If the heat pumps fails, the auxiliary heat becomes the primary heat. It is not efficient and should only be used until system is repaired.
How is auxiliary heat turned on?
It is turned on in stages to prevent a large inrush of amps if all of the heat strips were turned on at the same time.
What are the three uses of electric strip heaters in a heat pump?
1. Supplementary heat - when system is below balance point
2. Emergency heat - when the reverse-cycle heat pump is not working.
3. Air tempering- when the system is in the defrost mode.
Describe the flow of refrigerant through the reversing valve during heating mode.
From the outdoor coil, the cooler refrigerant enters the valve on one of the side lines, goes through slide and into the center line. From the center line, the refrigerant enters the suction line and goes through the accumulator and/or compressor. The ref
Should you always install gauges on a heat pump?
No- most heat pumps have a critical charge with tolerances of � 1/2 ounce. Do not install a gauge manifold each time you suspect a problem.
When the gas line is cold, what mode is the system in? When the gas line is warm. what mode is it in?
A cold gas line indicates that it is in cooling mode for the summer. When the gas line is warm, it is in heating mode for the winter.
How does a heat pump start defrost with an air pressure switch?
It measures the air pressure drop across the outdoor coil. When the unit accumulates ices, a pressure drop occurs and the air switch contacts close.