cja A/C & Heat Pump Compressor/Condenser Repair
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Photograph of This new compressor was placed directly against a brick wall. One third of its condenser coil cooling ability was blocked. Air Conditioning & Heat Pump Compressor/Condenser Unit

Home Page: Inspect, diagnose, repair or
replace the outdoor compressor/condenser unit

Outdoor air conditioner compressor unit inspection, diagnosis & repair guide home page.

This article series discusses the outdoor components of air conditioners and heat pumps and includes links to key articles that discuss in detail the outdoor and indoor components of an air conditioner or heat pump system including the outdoor compressor condenser unit and the indoor air handler, controls and ductwork.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

How do Air Conditioning Compressor / Condenser Units Work?

Air conditioning compressors overgrown with shrubs (C) Daniel FriedmanWhat is the "Compressor" unit in an air conditioner or heat pump system?

In a nutshell, the air conditioner compressor/condenser/fan unit is the "outdoor" half of an air conditioning or heat pump installation that uses a compressor motor to compress refrigerant gas to high pressure, sending the pressurized gas through cooling coils (condensing coils) where aided by air movement drawn by the condenser unit fan, the gas is returned to a liquid refrigerant state.

Photo just above: four outdoor A/C condenser units are installed too close together, out of level, and worst, their air flow is blocked by thick shrubbery. The effect of these common mistakes is a shorter condenser unit life and higher operating costs.

Article Contents

The process of compressing and then condensing the refrigerant back from a gas to a liquid also moves heat out of the refrigerant and into outdoor air. We explain this process in detail below.

The outdoor half of a typical air conditioning system (shown above) is a unit containing the refrigerant compressor and condensing coil and a cooling fan.

In our photo the dark colored screened surface covering one side of the condensing coil of the first compressor in this row is easily visible. The compressor motor itself (image shown below in this article) is not visible unless the covers of this unit are removed.

How the Air Conditioning Compressor/Condenser Unit Works to Move Heat from Indoors to Outside

Schematic of an air conditioner compressor unit showing inspection points (C) Carson Dunlop AssociatesIn this article we will sketch and explain the internal parts of an air conditioner compressor motor and the A/C condenser unit such as the compressor, condenser, and key controls.

The A/C Compressor 

The air conditioning compressor motor is a pump which draws sensible heat laden refrigerant gas from the building's indoor components (evaporator or "cooling coil" in the indoor air handler) through the larger diameter refrigerant suction line into the compressor where that pump compresses the low pressure refrigerant gas to high pressure and higher temperature.

Raising the coolant (refrigerant) temperature above outdoor ambient temperature causes heat to flow from the coolant (flowing out of the compressor and through the outdoor A/C condenser coil) into outdoor air. (Heat always flows from warmer to cooler substances).

Sensible heat and other terms are defined

at DEFINITION of HEATING, COOLING & INSULATION TERMS

Sketch courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

As we explain

at THERMOSTATIC EXPANSION VALVES,

it is the flow restriction provided by a cap tube or by a TEV in the refrigerant piping system that allows the A/C compressor pump to raise the system pressure and thus increase the temperature at which the coolant changes state.

In other words, the TEV or cap tube allows the compressor to reduce refrigerant pressure on the LOW side of the metering device and raise refrigerant pressure on the HIGH side of the metering device.

Incidentally, A/C compressors can only accept and compress refrigerant in gas form. In fact the refrigerant vapor is superheated to be sure that there is no liquid at the pump - lest the pump be damaged. If liquid refrigerant were to flow into the compressor motor it would most likely cause catastrophic damage.

Even with the covers off, you wont' see much of the actual air conditioner compressor motor: A/C compressor motors in residential and most commercial systems are hermetically sealed motors - that is, the motor is encased in a sealed steel can - all you'll see is a black metal container with metal (usually copper) tubing and some wires running to it.

Air conditioning compressor motor replacement unit (C) Daniel FriedmanThis is the compressor motor. In our illustration of a hermetically-sealed residential compressor motor (above right), the smaller cylinder to the right of the compressor is a filter/dryer built onto this replacement unit.

The A/C Condenser

The high pressure high temperature refrigerant gas leaves the outdoor compressor and enters the outdoor condensing coil where it is cooled to a liquid state by the condensing unit fan that blows outside air across the condensing coil or by immersion of the condensing coil in cooling water in some designs.

The heat produced in these steps is transferred to the outside by a fan which blows outside air across the condensing coil. The liquid refrigerant is then able to return to the indoor components for cooling and dehumidifying the building interior.

Definition of an Air Conditioner or Heat Pump

An air conditioner or heat pump compressor is a basically a motorized pump which moves refrigerant gas from the indoor cooling coil (where it has evaporated to cool indoor air blowing over that coil) to the outdoor compressor/condenser where the gas is compressed and cooled back to a liquid form.

Refrigerant gas moves from the indoor air handler cooling coil to the outdoor compressor via the larger refrigerant "suction line".

Liquid refrigerant returns from the outdoor compressor/condenser to the in-building air handler and evaporator coil. Evaporating liquid refrigerant inside the indoor cooling coil cools and dehumidifies indoor air. Condensing refrigerant gas outdoors at the compressor/condenser effectively is moving heat from indoors to the outdoor air.

[During heat pump "heating" cycles the process is reversed, moving "heat" from outdoor air to the indoor coil.]

The diagnosis and repair of various defects in the air conditioning compressor/condenser unit are discussed in detail using the links provided at the end of this article. Here is more detail about the components of the air conditioner or heat pump compressor/condenser unit:

Heat pumps are described separately and in more detail

at HEAT PUMPS.

Components of the Outdoor Portion of a Central Air Conditioning System

We have moved this discussion to a separate article. Please

see COMPRESSOR / CONDENSER UNIT COMPONENT PARTS

Air Conditioner or Heat Pump Compressor Unit Safety, Damage, & Environmental Warnings

Using Carrier installation instructions for the Carrier 24ANA unit as an example [2] and quoting:

[Compressor/Condenser] Unit Operation & Safety Hazard

Failure to follow this caution may result in minor personal injury, equipment damage or improper operation. To prevent compressor damage or personal injury, observe the following

Environmental Hazard Warnings - Failure to follow this caution may result in environmental damage.

Federal regulations require that you do not vent refrigerant to the atmosphere. Recover during system repair or final unit disposal.

Minimum Air Conditioner Compressor Unit Observations for an Air Conditioner Home Inspection Report

Example home inspection report language for an air conditioning compressor:

Types of air conditioner or heat pump compressors & compressor designs

Sealed Compressors

air conditioner heat pump compressor motor schematic © D Friedman at InspectApedia.com

Sealed air conditioning or heat pump compressors enclose both the driving electric motor and the mechanical compressor engine itself within a hermetically sealed "can".

Sealed compressors cannot be opened for repair in the field and are normally replaced entirely when needed.

The diagnosis of a sealed compressor relies on external observations and measurements such as current draws (amps) of the compressor motor and the operating pressures the equipment can achieve.

While a sealed hvac compressor unit can't be field-repaired, the unit can be replaced as an entire system, and in some cases the damaged unit can be traded in for an allowance on the replacement compressor.

What are those three tubes seen welded or soldered to the hermetically sealed HVAC compressor can? There are three tubes you'll find on a typical sealed compressor unit:

  1. A suction line

    (generally larger in diameter - low side line) - receives low pressure refrigerant gas from the cooling coil
  2. A condenser line

    (generally smaller in diameter - high side line) - sends high pressure refrigerant gas as compressor output to the condensing coil
  3. A third line, blocked off, not used in the field - the process tube.

    This tube is used by the manufacturer of the compressor unit to test and charge the system.
  4. 5-port HVAC or refrigeration compressors

    include a low side, high side, and process tube and two more tubes that send oil through an oil cooler or oil cooler condenser.

    The oil cooler condenser lines will always be close together and close to the bottom of the unit (to pick up oil to be cooled) - that's how you can identify which of those tubes coming in and out of the sealed compressor are doing which jobs.
  5. Power: You'll also see, of course, a connnection bringing electrical power to the compressor motor

Watch out: if you are carrying a refrigerator or freezer in other than upright position,

that is if you have to place the unit on its side, place it so that the low side (suction side) refrigerant lines are facing "up" so as not to drain oil or liquid refrigerant into a line where it does not belong and where it may block a cap tube.

If you make a mistake and carry the appliance in the wrong position, you would be smart to leave it in the upright or operating position for a few hours before turning it on to avoid forcing a slug of oil into (and blocking)

the CAPILLARY TUBES

often used on home refrigerators or freezers.

Leaving the system upright allows oil that may have leaked into the refrigerant line to drain back into the compressor motor. If you turn on the system too soon the risk is that you push this oil into the cap tube where it may remain or be hard to get out or worse, you may leak oil into the reed valves where they will be damaged when the compressor motor is turned on.

Open type refrigeration compressors

Open type refrigeration compressors are commonly found on automotive air conditioning systems. The motor that drives the actual compressor (the mechanical engine that compresses refrigerant gas) is physically separate from the compressor and is located outside of it.

Typically a motor drives the compressor via a belt and pulley system (cars and some commercial refrigeration systems).

This is why you should run your automobile air conditioner from time to time even out of the cooling season - to lubricate the shaft seal around the compressor motor/pulley - that's a spot where refrigerant may leak out at a dried seal.

Semi-sealed HVAC compressors

Semi-sealed compressors can be disassembled and repaired, as can the open type above.

Air Conditioner / Heat Pump Compressor Valves - two common designs

All compressors have a suction and a discharge valve to control refrigerant flow through the unit.

Reed Valve refrigeration compressor motors

Often the valve is a reed design - in which case the bottom reed is the intake valve and a top mounted reed is the discharge reed or valve that discharges out through a noise muffler into the condenser piping and coil.

It is these valves that can be destroyed if liquid refrigerant is sent through the compressor.

Rotary valve refrigeration compressor motors - Frigidaire rotary compressor motors

Frigidaire eccentric crank rotary compressor design sketch © D Friedman at InspectApedia.com

[Click to enlarge any image]

Some other refrigeration compressor valve designs are quite different from these simple reeds, including an old and very successful eccentric crank system: the rotary compressor motor design patented by Frigidaire™ and used in refrigerators for several decades.

This compressor motor design was used in a range of Frigidaire equipment and appliances including refrigerators and some air conditioners.

The durability of the design stems at least in part from its simplicity: a simple eccentric crank (see our sketch at left) is the only moving part in the motor. My illustration above is of course simplified.

On this compressor motor the inlet or suction line is generally found on the bottom of the unit, feeding directly into the bottom of the piston assembly and sealed from the rest of the chamber. The interior of the compressor chamber (sketch note and arrow at left) is on the HIGH side of the system. So service valves, if they are installed at all, are placed on the high side of the system there.

Frigidaire eccentric crank rotary refrigeration compressor motors were remarkably durable and reliable.

After the Dutchess County Boces class I (DF) took on refrigeration motor repair, the next spring during "Spring Cleanup" when people toss out old appliances, we drove around looking for old Frigidair refrigerators that were being tossed out.

Invariably the motor, which was indestructable, still worked.  I found one and made it into my working compressor motor that I used when I needed one to service (pull a vacuum) on other HVAC equipment. All I had to do was braze on service valves on to the motor's hig and low refrigerant lines and of course put a plug on its power wire. 

I continued to use that salvaged Frigidaire refrigerator compressor as our HVAC service vacuum pump for many years.

Air Conditioner / Heat Pump Compressor Motor Refrigerant Oils

Refrigeration compressor motors use 300 viscosity oils when working with refrigerants in the Freon family and 150 viscosity oils when working with other refrigerants. These are special oils that use a non-wax base such as Texaco Capella oil or oils by Virginia Chemical.

The refrigeration oil lubricates the moving parts of the compressor motor as it receives and compresses refrigerant gases.

At TYPES of AIR CONDITIONER or HEAT PUMP COMPRESSORS when we warned that carrying a refrigerator or freezer on its side could drain oil out of the compressor motor into the refrigerant lines where it might later become a problem by blocking the capillary tube or might enter reed valves causing valve damage, this is the oil we were talking about.

How to diagnose and fix an air conditioning system that is not working

Schematic of an air conditioner compressor unit showing inspection points (C) Carson Dunlop AssociatesAre You Troubleshooting an air conditioner or heat pump compressor/condenser unit?

For steps that a building owner or occupant might take before calling a service technician

see DIAGNOSTIC GUIDE A/C or HEAT PUMP

If your air conditioning system won't work, use these easy A/C-heat pump diagnostic guides

Specific A/C or Heat Pump compressor diagnosis & repair procedures listed just below:

Sketch of the condenser unit shown above was provided courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing company.

List of air conditioning system diagnostic articles:

See our complete list of air conditioning system diagnostic and repair guide articles just below.

Since the failure of an air conditioner to turn on, loss of air conditioner cooling capacity, reduced air conditioning output temperatures, loss of cool air supply, or even loss of air flow entirely can be due to a variety of problems with one or more components of an air conditioner or air conditioning system,

after reviewing the lost air conditioner cooling diagnosis procedures described in this article, be sure to also review the diagnostic procedures at each of the individual air conditioning diagnosis and repair major topics listed just below.

If your air conditioning or heat pump system has lost its cooling capacity or won't start,

or if your air conditioning electrical bill has increased even though the system "on" time has not changed, select one or more of the diagnostic articles listed at

AIR CONDITIONING & HEAT PUMP SYSTEMS - home -

Life of an Air Conditioning or Heat Pump Compressor?

10-20 years, sometimes longer.

Please see complete details at AIR CONDITIONER/ HEAT PUMP LIFE EXPECTANCY - including the factors that impact air conditioner or heat pump life.

 

...


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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Condenser fan sounds like a helicopter and is getting louder

My heat pump outdoor 2 blade condenser fan sounds like a helicopter and is getting louder - On 2019-12-18 by Tibor -

Reply by (mod) -

Tibor

See NOISES, COMPRESSOR CONDENSER

also, in the ARTICLE INDEX you'll find our article series on NOISE DIAGNOSIS that describes various sounds coming from heating and air conditioning equipment and the usual causes. That would be a great place to start. Don't hesitate to ask questions.

mon compreseur sali 10minit es saret 30minit

mon compreseur sali 10minit es saret 30minit - On 2019-08-13 by cheikh -

Reply - by (mod) -

You might try the search box above to find our article on

THE COMPRESSOR/CONDENSER TURNS ON & OFF TOO FREQUENTLY

Refrigeration unit fan not working

hi sir
i have samsung refrigerator model RS22FLMR that has problem
first the condenser fan (12 volts)n ot working ,,i replace it still not working ,

i replaced it with a 220volts fan it works good but the compressor start once when i powered the refrigerator on than wont start again until I un-plug and re-plug in the power cable so he start once again
what should i do plz

is it becose of dc 12 v fan not connected to board so compressor wont start again? or board problem or what u think about that . - On 2019-05-21 by Farid -

Reply by (mod) - high head pressure: compressor can't start

Farid

When a compressor motor has trouble starting in the manner you describe I suspect a refrigerant metering device clog - such as a clogged cap tube.

If the compressor is facing high head pressure on its outlet side it can have trouble starting.

...

Continue reading at COMPRESSOR / CONDENSER DIAGNOSTICS - step by step diagnosis, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see COMPRESSOR / CONDENSER REPAIR FAQs - posted originally at this article

Or see these

Recommended Articles

Suggested citation for this web page

COMPRESSOR / CONDENSER REPAIR at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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INDEX to RELATED ARTICLES: ARTICLE INDEX to AIR CONDITIONING & HEAT PUMPS

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