Enter Search Terms Below and press 'ENTER' Top 14 Things You Should Know About Your Air Conditioning System two easiest and most important We accept cash, check, and all major credit cards OUTDOOR UNIT FREEZING-UP - The outdoor unit forms an abnormal amount of ice on the outdoor coils that does not go away after an hour. * It is normal for a heat pump to develop frost on the outdoor coil during cold temperatures.  A normal defrost cycle should take place to thaw the coil.  During defrost mode the outdoor fan motor stops, the reversing valve switches into cooling mode and the compressor continues to operate.  It is normal to see steam coming out of the outdoor unit during a defrost cycle. POSSIBLE PROBLEM & DESCRIPTION Ice Covering Top of Unit It is not unusual after freezing rain or snow thawing for water to freeze over the top of the fan discharge of the outdoor unit.  This can either stop the fan from turning or prevent air from discharging from the unit. 

In either case, the ice needs to be removed for the unit to function properly. Do not try to remove ice or any other objects from the fan path with power on the unit.  Always pull the service disconnect switch near the unit or turn off the breaker before attempting any repairs. It may be necessary to switch the thermostat to "Em Heat" until the unit thaws or repairs are made. Failed Outdoor Fan - Qualified Technician Recommended If the outdoor fan motor quits running while a heat pump is operating in the heating mode, the outdoor coils will quickly freeze and a defrost cycle may fail to remove all of the ice. A stopped fan motor can be the result of a bad motor, bad start capacitor (below), or faulty control board or relay. Bad Capacitor - Qualified Technician Recommended Low Freon - Qualified Technician Recommended If a heat pump becomes low on refrigerant it may not be able to produce enough heat in a defrost cycle to thaw the outdoor coil. 

This would be seen in a heat pump that enters and stays-in defrost mode for about 10 minutes and then exits defrost with a substantial amount of frost or ice still covering the coil. Bad Defrost Control - Qualified Technician Recommended There are two types of defrost controls - Time & Temperature or Demand Defrost. Time & Temperature controls use a defrost thermostat and a timer board. Time & Temperature boards typically have a setting for 30, 60 or 90 minutes.  When the coil temperature drops below 30 degrees a defrost thermostat should close, starting the timer on the board.  After the selected time period the control board should initiate a defrost cycle. Demand Defrost boards measure the outside air temperature and the coil temperature to determine the optimum conditions for a defrost cycle to take place. Bad Defrost Sensor/Thermostat - Qualified Technician Recommended The defrost thermostat should "close" when the coil temperature is below 30 degrees. 

A bad defrost thermostat will prevent a Time & Temperature defrost control from entering a defrost cycle.ac units for electrical panels Either a bad outdoor sensor or coil sensor can cause a Demand Defrost control to not defrost properly.ac unit lattice < Prev Next >portable ac unit for sale We are excited to have you become a member of the General Heating & Air Conditioning family. To schedule an appointment all you need to do is Call Today or Click Here for online chat We provide useful tips and information for homeowners, facility managers and contractors looking to improve their current HVAC system. Since the minimum efficiency regulation changed to 13 SEER in January 2006, most OEM systems now incorporate a thermostatic expansion valve (TXV) style metering device as the standard for air conditioning systems.

It is now extremely important for the HVAC technician to understand the design and operation of this type of valve. The thermostatic expansion valve (TXV) is a precision device, which is designed to regulate the rate at which liquid refrigerant flows into the evaporator. This controlled flow is necessary to maximize the efficiency of the evaporator while preventing excess liquid refrigerant from returning to the compressor (floodback). One of the design features of the TXV is to separate the high pressure and low pressure sides of an air conditioning system. Liquid refrigerant enters the valve under high pressure via the system’s liquid line, but its pressure is reduced when the TXV limits the amount of this liquid refrigerant entering the evaporator. The TXV – What It Does Do The thermostatic expansion valve controls one thing only:  the rate of flow of liquid refrigerant into the evaporator. Contrary to what you may have heard, the TXV is designed to control:

Trying to use the TXV to control any of these system variables will lead to poor system performance – and possible compressor failure. How the TXV Controls the System As the thermostatic expansion valve regulates the rate at which liquid refrigerant flows into the evaporator, it maintains a proper supply of refrigerant by matching this flow rate against how quickly the refrigerant evaporates (boils off) in the evaporator coil. To do this, the TXV responds to two variables: the temperature of the refrigerant vapor as it leaves the evaporator (P1) and the pressure in the evaporator itself (P2). It does this by using a movable valve pin against the spring pressure (P3) to precisely control the flow of liquid refrigerant into the evaporator (P4): TXV Pressure Balance Equation P1 = Bulb Pressure (Opening Force) P2 = Evaporator Pressure (Closing Force) P3 = Superheat Spring Pressure (Closing Force) P4 = Liquid Pressure (Opening Force) Energy Transfer in the TXV

Here is a closer view of the TXV in operation. The flow of the liquid refrigerant is restricted by the valve pin. As the flow is restricted, several things happen: The pressure on the liquid refrigerant drops A small amount of the liquid refrigerant is converted to gas, in response to the drop in pressure This “flash gas” represents a high degree of energy transfer, as the sensible heat of the refrigerant is converted to latent heat The low pressure liquid and vapor combination moves into the evaporator, where the rest of the liquid refrigerant “boils off” into its gaseous state as it absorbs heat from its surroundings. The pressure drop that occurs in the thermostatic expansion valve is critical to the operation of the refrigeration system. As it moves through the evaporator, the low pressure liquid and gas combination continues to vaporize, absorbing heat from the system load. In order for the system to operate properly, the TXV must precisely control the flow of liquid refrigerant, in response to system conditions.