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Air Conditioner Compressor Troubleshooting

  • REFRIGERANT LOW HEAD PRESSURE DIAGNOSIS - CONTENTS: what causes low head pressure at the refrigeration or air conditioning compressor or piping system? Diagnostic checklist for refrigerant charge quantity, leaks, undercharging. How to figure out if there is too little refrigerant or "freon" in an air conditioner or heat pump, refrigerator or freezer or other cooling systerm.
  • POST a QUESTION or READ FAQs about refrigerant pressure readings in air conditioners, heat pumps, & other refrigeration equipment
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Low HVACR compressor head pressure diagnosis:

What are the causes of low head pressure at the air conditioner or heat pump compressor? What are the effects of low refrigerant pressure at the compressor or in the system? Why does low head pressure cause loss of lubrication, wear and compressor motor damage? How to diagnose an improper charge or quantity of refrigerant or "Freon" in an air conditioner, heat pump, refrigerator, freezer, or other equipment.

In this article series we explain how overcharging or undercharging of refrigerant in an air conditioner or heat pump is detected and we list the effects of overcharged or undercharged refrigerant. We also explain the various causes of liquid slugging a compressor motor.

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Refrigerant Pressure Diagnosis: Causes of Low Head Pressure in HVACR Systems

Photograph of a
commercial air conditioning compressor charging chartLow head pressure may occur simulataneously with high pressure on the suction side of an air conditioner, heat pump or refrigeration system compressor system.

If the system is continuing to cool it may be doing so at reduced capacity, observed as a loss of up to ten degrees of temperature drop across the coil. The two most common causes of low head pressure at an air conditioner or heat pump compressor motor are:

Less common causes of low head pressure

Effects of Low Head Pressure at the HVACR Compressor

Effects of low head pressure in a refrigeration system incude more than reduced cooling capacity of the system. On commercial systems (and maybe some residential systems) the reduced head pressure can cause refrigerant oil migration or more specifically, the system may be unable to push oil through the cooling coil (the evaporator coil) until it accumulates as a bolus of oil that suddenly returns in one shot tothe compressor.

The effects of poor oil return to the compressor include first reduced cooling capacity and later damage to the compressor motor. If the liquid line is not warm on your system you may face these problems. (A-1 Compressors 2009).

Smaller air conditioners or refrigeration equipment whose design does not include a refrigerant accumulator are at increased risk of damage from overcharge, liquid slugging, or oil circulation problems. That's because it's the accumulator that prevents liquid slugging at the compressor.

Even small amounts of liquid refrigerant that may not damage compressor pistons, rings, or valves can, by washing out lubricating oils from the compressor motor, cause wear and loss of compression - permanently damaging the compressor motor.

References for Low HVACR Compressor Motor Head Pressures

If your air conditioning or heat pump system has lost its cooling capacity or won't start see REPAIR GUIDE for AIR CONDITIONERS.


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