Refrigeration Cycle Component Diagram for Air Conditioners and Heat Pumps
Richard - What are pressure switches used for in refrigeration circuits and how do pressure switches protect the system from further damage?
Refrigeration Pressure Switches
Thanks for the question and for being a reader of High Performance HVAC! First there two types of basic refrigeration switches in the typical high grade residential system. I say high grade because not every refrigeration system in air conditioners and heat pumps have switches to protect the refrigeration system.
High Pressure Refrigeration Pressure Switches - The high pressure switch will kill the compressor circuit if the pressure exceeds the rating on the pressure switch. The ratings will vary depending on the type of refrigerant the air conditioner or heat pump uses in the system. On some air conditioners or heat pumps this switch is manually reset only simply because if it trips there is definitely a problem that needs to be resolved before the system should run again. On Rheem and Ruud heat pumps and air conditioners the reset button is usually red on located near the control panel. A simple push of the switch will reset the switch and the operation of the air conditioner should return to normal until the pressure exceeds the rating of the switch. Things that can cause the pressure switch to trip include:
Bad condenser fan motor
Coils plugged up with dirt and debris
Fins on the coils bent
Blockage in the refrigeration system
These issues, if they exist, should be taken care of before before the switch is reset. The high pressure switch prevents the system from operating at extremely high pressures.
Low Refrigeration Pressure Switches - The low pressure switch is typically an automatically reset switch that will reset itself when the pressure on the low pressure side of the refrigeration systems returns to normal or above the setting on the switch. When a refrigeration system operates at lower than normal pressures the system can freeze up with the freezing beginning at the evaporator coil and working its way back to the compressor via the suction line. Freezing of the refrigeration system is bad and lead to liquid refrigerant slugging in the compressor which can lead to compressor failure. Things that can cause the low pressure switch to trip include:
Low refrigerant charge from a refrigerant leak
Blower motor failure in the air handler
Plugged evaporator coils or a blockage of air flow
Failure of a refrigeration component in the refrigeration system
Again, if these issues exist in the refrigeration system they need to be addressed to prevent the low pressure switch from tripping. In some cases such as catastrophic failure or loss of the refrigerant charge the system will not run at simply because the controls were engineered correctly to prevent short cycling however it is possible the system can short cycle especially if the condenser has been re-engineered with aftermarket parts by someone who knew enough to be dangerous. This includes myself in certain instances however I always do my best to think things through before making a change to the system. After all, solving one problem only to create another problem is not fixing the HVAC system. Number one is safety and reliability and number two is protecting the system from permanent damage keeping number one in mind.
These switches are used for a specific purpose and re-engineering the HVAC system can create other problems. It is also important that the person making the changes is competent or has someone competent review the changes to make sure other problems will not be created. When engineered properly these devices can protect the system and save you tons of money in the event of a catastrophic failure of the system for any reason whether it is a system defect or it is a child playing that damages the unit.
This high SEER Trane condenser uses an ECM variable speed fan motor to modulate the speed of the fan
Variable Speed ECM Condenser Fan Motors are used in condensers for the high efficient models so that the fan speed for the condenser can be modulated according to the load of the system. The ECM fan motors are used in condensers that either have a modulating compressor or condensers that have two compressors where one compressor is small and one compressor is large. The ECM motor adds to the efficiency of the system by modulating the condenser fan motor to match the compressor use needed to satisfy the load.
Variable Speed ECM Condenser Fan Motors - Peak Operation
On very hot days you need more air conditioning capacity to satisfy the heating load demand put on your home in the summer. In milder weather you do not need to run the air conditioner at 100% to satisfy the higher demand. HVAC equipment manufacturers have introduced systems that have the ability to run in two-stages so that on the hotter days you can satisfy the demand and on the cooler days you can run the system at a lower setting thereby using less energy.
Using less energy is the objective so how do we do this? The solution is two-fold for having an efficient running system. One is to reduce the heat gain by insulating the home and adding things to the home such as attic fans. These things help reduce heat gain to the living areas that you want to condition with cool less humid air. The second thing you can do is to purchase a higher efficient system that can modulate or offers staging from a high level for higher demand to lower level for lower demand.
Variable Speed ECM Condenser Fan Motors - The Future
HVAC Manufacturers introduced two-stage compressors and in the future (offered currently in commercial systems) modulating compressors that will run according to the demand based on exactly what you need to condition your space. Since the compressor would stage based on demand they needed a condenser fan motor that would also stage based on demand. Some manufacturers use a standard multi-speed fan motor while others use a ECM fan motor to facilitate a higher speed for the increased demand when the system is calling for higher demand and a lower speed when the system is calling for a lower demand. So when the compressor is running at a higher speed the condenser fan motor will also run at a high speed and when the compressor is running at a lower speed the fan motor will run at a lower speed.
An ECM Variable Speed Blower Motor in a squirrel cage blower
Variable Speed ECM Blower Motors - Variable speed blower motors have become increasingly popular in residential air conditioning and heating systems and for good reason; these motors increase efficiency of the systems and offer a whole range of other benefits that help the system and the consumer.
Variable Speed Blower Motors first offer a higher efficiency for air conditioning systems based on the manufacturers set up of the control with the ECM Variable Speed Motor. Each manufacturer calls it a different thing such as Trane calling it the Comfort R and Carrier calling it Infinity Control. Despite what the manufacturer calls it helps efficiency with air conditioning by starting the blower slowly and letting it run at a 50% speed for the first few minutes (up to 7 minutes) to remove more humidity. This increases comfort and efficiency by removing more moisture from the air. The lower the humidity in the cooler you will feel so the variable speed blower with this type of control will enhance comfort.
ECM variable speed motor manufacturers include General Electric and Emerson with Emerson offering their very own packaged control and control program to meet various control sequences to meet efficiency and comfort for any manufacturer that uses the Emerson variable speed ECM blower motors for their equipment.
Other benefits include:
Soft start capabilities which reduces high inrush current like conventional blower motors.
Precision control to deliver a set amount of CFM's for whatever the HVAC equipment manufacturers need for their equipment for airflow control.
High efficiency which reduces energy bills.
Very quiet operation
Better comfort as described above
One of the disadvantages include a high replacement cost if something happens to the motor or controls. ECM variable speed motors need the attention of a qualified HVAC technician if something goes wrong as special diagnostic tools are needed to diagnose any problems which may arise with the motor or controls.
These motors are typically offered in the medium to higher end models of air handlers and furnaces so you will have to pay a little more for the initial cost but the benefits will give you a pay back in the future with increased comfort and higher efficiency. Here at High Performance HVAC we always recommend going for higher efficiency models because the cost of energy is not going to go down in the future and the high efficiency models will help reduce the cost of energy so your utility bills will be reasonable in the future. The bonus this air handler or furnace component also adds comfort while increasing efficiency.
Never assume the blower motor is bad. Always perform a cursory look at other components and inputs before condemning the ECM blower motor. Check the air filters and duct work integrity before beginning component checks outlined below. The system needs good air flow to function properly.
Check the main control board in the air handler. Wiring connections including the thermostat wire coming from the thermostat. Always perform these checks with the power turned off. Check for loose connections, corrosion, and burned spots on the board. Some HVAC equipment has an additional control board for control of the ECM blower motor in the air handler. Also check all the connections going to the motor including pins inside the molex plug connection. A bent or loose pin will cause problems.. A plastic molex plug should make the connection between the motor and the control board.
Next check the input voltage for the board. Restore power and use a volt meter to check both the main line voltage and the control voltage. The control board should use 24 volt for the control voltage and all voltage ranges should be plus or minus 10%. Make sure that the safety circuit is good. Switches in the safety circuit will keep the system from running.
Using the manufacturers instructions, check additional settings on the control board. Many have dip switches that will control RPM's for the proper air flow for the sizing requirements of the system. Ensure these are set properly.
Ensure when you start the system that you wait for the programmed delays. An ECM blower motor, properly programmed, will start off very slow and then ramp up to a low speed according to what the program calls for. After a specific period of time, usually around 7 minutes, the blower will ramp up to 100% of the program according to where the dip switch settings is set for RPM's or CFM's.
If this doesn't work then and you still have problems check with the manufacturer for a ECM blower motor troubleshooting flow chart or guide. Some manufacturers have a diagnostic tool that will confirm specific problems and can indicate if the motor or the controls are bad. If the motor is turning too many RPM's or not enough RPM's and is causing issues with the air conditioning or heating system because of improper air flow then it is a good idea to check the dip switch settings on the board. Good luck.
The condensing unit fanis responsible for pulling air through coils of the condensing unit. They pull air through the condensing unit coils. It runs the gamut in horsepower ratings from low fractional horsepower in small residential units all the way up to 1 horsepower (and larger) 3 phase motors in large commercial HVAC units. It is usually direct drive to a propeller blade which creates the air flow. Its job it to move air. A specific quantity of air through the condensing unit coils so that a heat exchange process can take place and rig the condensing unit of the heat it absorbed indoors or in the case of the heat pump in heating mode to absorb heat from the outside air and send it inside. It is the process of refrigeration and all the components work together to achieve one result and that is to move heat from one place to another.
In straight air conditioners the air conditioner fan is used mainly in the summer or when the air conditioner is running. During the winter this fan sits idle until the air conditioner is turned back on in the spring when temperatures begin to rise.This can be a problem for the air conditioner motor. Sitting all winter without any motion the bearings and shaft in the air conditioner motor can seize up or rust. It is important that the air conditioner motor be checked to ensure it is running especially when it is first turned on after sitting idle all winter. This is a good reason to have air conditioning spring maintenance performed by a professional.
Gas furnace ignition controls vary from furnace manufacturer to furnace manufacturer. Some are proprietary and some are from an engineering company which specializes in gas furnace ignition controls. Honeywell being a major manufacturer of controls for HVAC also makes several gas furnace ignition controls. Gas furnace ignition controls have advanced by leaps and bounds over the last 20 years coming from the norm which was standing pilot ignition all the way to solid state ignition controls which exist today and are safer and more efficient than the gas furnace ignition controls of yesteryear. Aside from a few companies which lag behind in technology for whatever reason to some water heater manufacturers who continue to adhere to the old standing pilot ignition controls the new modern systems offer safety and efficiency in all their gas furnace controls. Honeywell was the pioneer as they are with much of the modern HVAC technology and Lennox and Carrier came in just behind Honeywell with advancements in engineering of gas furnace ignition controls that changed the entire HVAC gas furnace industry.