Richard – What are refrigeration pressure switches used for in refrigeration circuits and how do refrigeration pressure switches protect the system from further damage?
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 refrigeration switches to protect the refrigeration system.
High Pressure Refrigeration Switch – The high pressure switch will kill the compressor circuit if the pressure exceeds the rating on the pressure switch. These pressures 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:
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 Pressure Switch – 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:
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 use in condensers for the high efficient models so that the fan speed for the condenser fan motor can be modulate according to the load of the system. The variable speed ECM condenser 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 variable speed ECM condenser fan motor adds to the efficiency of the system by modulating the condenser fan motor to match the compressor use needed to satisfy the load.
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.
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 condenser fan motor while others use a variable speed ECM condenser 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 condenser fan motor will run at a lower speed.
An ECM Variable Speed Blower Motor in a squirrel cage blower
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 ECM variable speed 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.
Troubleshooting ECM Blower Motors Basics
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 condenser fan motor is responsible for pulling air through coils of the condenser. The are also call air conditioner fan motor or heat pump fan motor but they all serve the same purpose. They pull air through the condenser coils. The condenser fan motor 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. The condenser fan motor is usually direct drive to a propeller blade which creates the air flow.
In straight air conditioners the air conditioner fan motor is used mainly in the summer or when the air conditioner is running. During the winter this motor 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 fan motor. Sitting all winter without any motion the bearings and shaft in the air conditioner fan 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. Continue reading “Condenser Fan Motor – Air Conditioners & Heat Pumps” »
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.
Always follow the thermostat manufacturers instructions whenever changing the thermostat. Always turn the power off at the air handler and the condenser and make sure there is no voltage at the transformer before proceeding. The colors below are the most likely colors used for most installations however your thermostat wire colors may be different than what is indicated here. There is no official standard for thermostat wire colors. Thermostat wiring colors are not standardized but these are the most wiring methods used based on my years of experience in the HVAC field where I successfully wired a lot of thermostats. For instructions on how to wire a thermostat please see our how to wire a thermostat page.
HVAC single phase compressors always come hooked up to a run capacitor to help the compressor when it is running however very few HVAC compressors come with a start capacitor. Most HVAC technicians know that the air conditioner or heat pump compressors pulls a lot of amps on start up and this large amount of amperage draw on start up is referred to technically as locked rotor amps or inrush current and can be as much as 40,000 watts or more of pure power to get an HVAC compressor started. That large amount of amperage on the compressor windings over and over again can slowly degrade or eat away at the life of the compressor as it starts over and over again during the summer for the air conditioner and year round for the heat pump. The run capacitor does little to help the compressor on start up so in certain circumstances the manufacturer will recommend installing a start capacitor on new installations and it is a prudent thing to add a start capacitor to older installations where we need to give the compressor a slight boost on start up. There are two ways we can do this job of helping the compressor start. The first method is usually for older installations on compressors that are having issues starting and most technicians use this method when they encounter a compressor with problems. The technicians use a hard start kit which is usually available at the local HVAC supply house and is easily hooked up to the compressor wiring following the directions on the hard start kit wiring diagram. Of course every HVAC tech knows it is important for safety to turn off the power to the unit and discharge any capacitors before proceeding otherwise serious injury or worse can occur. Continue reading “Start Capacitors for HVAC Compressors” »
My furnace is leaking water and it is summer time so I am not using it for heat except for the blower fan which is hooked up for the air conditioner and the heat. I know the pipes from the outside units run into a box on top of the furnace so I think that is a part of the air conditioner. What can I do to fix the problem if you know what the problem is by my explanation here?
Air Conditioning Units & Heat Pumps Condensing Unit Basics
Air Conditioning & Heat Pump condensing unit is a simple yet technical piece of HVAC equipment. It sits out in the back (or side) of your house and kicks on and off almost by itself. At least it seems that way to most people. In this box made of sheet metal, is the heart of your HVAC cooling system. Or for those with heat pumps, it is the heart of your HVAC heating and cooling.
A heat pump condensing unit will look similar to an air conditioning condenser. There are differences inside the the heat pump condenser and air conditioning condenser equipment. A heat pump condenser has a reversing valve and an air conditioner condenser does not have a reversing valve. A heat pump will provide heating and cooling and an air conditioner will only cool your home or business. Both systems are common in the fact that both types of condensers have condenser coils, a compressor, controls, and a condenser fan motor. Unless you have a water to air heat pump system you probably do not have a heat pump if you live North of the Mid-Atlantic region (North of Maryland).
Every electrical-mechanical piece of equipment has a sequence of operation and while some manufacturers of heat pumps vary slightly with their heat pump sequence of operation but overall the sequence of operation for a heat pump is the same for most manufacturers. So unless you have a special type of heat pump (they are out there – the Acadia heat pump is designed for extreme cold weather temperatures up North like Canada) the sequence of operation for your heat pump should be very similar to what I described here. This is the basic heat pump sequence of operation like you will find in conventional heat pumps.