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Delay Timers and the Air Conditioner Condenser - Unit with the top off - condenser fan motor
Delay Timers and the Air Conditioner Condenser - Air Conditioners are big HVAC refrigerators. Air Conditioners and Heat Pumps use the HVAC refrigeration cycle to transfer heat from a place where it is not wanted (inside absorbing heat with the evaporator coil) to a place that makes no difference (outside using the condensing unit)(in the cooling cycle). The heart of any HVAC air conditioning, heat pump, or refrigeration system is the compressor which pumps the refrigerant through the HVAC air conditioning system.

When the refrigerant leaves the compressor it is compressed and therefore a higher pressure than it was before it entered the compressor inside the condensing unit. This pressure remains constant (give or take under certain conditions) until it passes through the metering device where the pressure and temperature are reduced. This low pressure remains constant (again give or take under certain conditions) until it again reaches the compressor inside the condensing unit and is compressed again.

Pressure Equalization in the Condenser

When you turn the air conditioner condensing unit off these pressures equalize within five minutes. The equalized pressure is often referred to as static pressure to HVAC professionals. The high side pressure on a hot day can be as high as 300 P.S.I. and higher in some systems. If your HVAC system is not equipped with a delay timer and you turn the system on within five minutes of turning it off, the compressor inside the condenser must start against that higher pressure. That is not good for the compressor and could possibly damage it.

Problem

The HVAC air conditioner condensing unit compressor should not be started unless the air conditioning or heat pump system is at the static pressure. I have responded to calls where the air conditioner or heat pump condensing unit was not equipped with a delay timer and the air conditioning or heat pump condensing unit was inadvertently started before the pressures were allowed to become static. Often the compressor inside the condenser is locked up, the run capacitor is shot, a fuse is blown, a breaker is tripped, the compressor is damaged mechanically or electrically beyond repair, or a combination of any of these things mentioned.

HVAC Condensing Units and Compressor Mechanics – Delay Timers and the Air Conditioner Condenser

If the homeowner is lucky, the only thing wrong is the capacitor or fuse. The run or start capacitor for your compressor can be replaced for a minimal cost compared to replacing a compressor. If the compressor is locked up there is a chance that it can be unlocked (note the word chance). A hard start kit and a good rap with a hammer can sometimes do the trick. If this doesn’t unlock the compressor then you will have to replace the compressor or the air conditioning or heat pump condensing unit. It is often in the homeowners best interest to replace the condensing unit.

Before this happens to you, call the company you often deal with to maintain and repair your HVAC system(s). Ask to speak with the HVAC service manager or HVAC technician that has worked on your HVAC equipment. Ask them if your condensing unit is equipped with a delay timer. They should be more than happy to answer your question…………and if they are not sure ……check to see if the condensing unit is equipped with a delay timer. You may want to have the model number, serial number (for both the condenser and air handler), and type of thermostat you have. Most modern digital and programmable thermostats have delay timers built into them.

Delay Timers and the Air Conditioner Condenser - Digital Thermostats

If you have an older mechanical thermostat it’s a good idea to make sure you have a delay timer in your condenser. Ask your HVAC contractor to make sure you are protected against this problem.

Air Conditioner Service and Repair - another great article to help you from High Performance HVAC

For more on air conditioners click here.

High Performance HVAC Air Conditioning and Heating SystemsDelay Timers and the Air Conditioner Condenser

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