The Heart of any
Air conditioning or refrigeration system
is the Compressor.
Compressors usually work or they don't
The compressor on an air conditioner or heat pump is usually misunderstood. It is a pump driven by an electric motor it has valves, pistons or vanes and is constructed somewhat like an automotive engine. A scroll compressor uses a set of spirals and is more efficient because there is no reciprocating parts. You may also find rotary compressors which act like a vane pump.
with little in between
Rotary compressors are not used very often in larger systems but are common with window units.
The compressors on a residential heat pump or air conditioner is usually hermetic that means the motor and the part that pumps is built into one box also called a can.
The electric motor is installed in the can so the refrigerant flows over the motor windings to cool it as it runs. The insulation of the motor windings is like any electric motor that it is covered with varnish that doesn't react with the refrigerant unless it becomes acidic. Then the insulation gets eaten off the windings and the motor burns out. If you are lucky the circuit breaker or fuse will blow. If not then the motor will continue to run and ruin the refrigeration system. A system that is short of refrigerant (aka Freon) will overheat the motor a system that is overcharged can flood the compressor causing "liquid slugging". A bad crankcase heater will also cause damage due to liquid. This is not as much a problem on smaller systems but will destroy larger units or systems with a lot of refrigerant charge. To learn more about the proper charge I have created this page.
When a hermetic compressor fails the only way to fix the system is to replace it. When it is replaced it is necessary to install filter dryers to clean up the system of moisture and acid that will be introduced from opening the system and left from the failure.
The motor in a compressor if not 3 phase is usually a capacitor start capacitor run type. It will have a start capacitor and a run capacitor. If the run capacitor fails the motor will not start and draw excessive current than it should and over heat (tripping) it's internal protector (also known as an "overload"). If it doesn't have a start capacitor it probably should. Especially if it has problems starting under load. If the cooling coil is replaced with one that has a thermostatic expansion valve as opposed to capillaries or an orifice. You may think that the compressor is bad because it won't start. Scroll compressors do not need start components but they DO need and anti restart timer or they can run backwards if the power is interrupted. A rotary compressor can do the same thing under certain conditions.
For more on this subject please visit the problem solving page and the cooling homepage.
The most common brands of compressor are Bristol, Tecumseh and Copeland. Other brands include Manurope, Trane, Danfoss, Aspera, Dunham Bush, Carlyle (Carrier) and York.
Picture of Carrier compressors in an old water cooled system. Note oil pressure safety controls and Ranco dual pressure control. To learn more about this system follow this link. The large device on the upper right is a suction line dryer used as a liquid line filter to get rid of crud in this system from past problems.
Common Problems with residential units.
More to be added later
It is 3 am Eastern Time When I wrote this
More to be added later.
- Compressor will not start some or most of the time, fan runs at full speed (reciprocating compressor single phase). Add a start kit or repair start components. A bad run capacitor could do the same thing.
- Compressor and fan will not start (single phase unit with combination capacitor). Bad combination run capacitor.
- Compressor trips breaker or blows fuses as soon as power is applied (1 pole contactor). Compressor is grounded, replacement is the only cure. You will read a low ohms reading from one or more of the compressor terminals to ground. NOTE:!!! fan may turn slowly all the time if the one fuse blows on the switched side of the line in disconnect or panel. Your fan motor may not be bad.
- Compressor trips breaker or blows fuses as soon as contactor is pulled in (two pole contactor) same as above...
- Compressor draws no current fan runs normally. An open motor overload protector or burned off common wire. If compressor is hot wait for overload to reset. If overload does not reset replace compressor.
- Same as above but one winding is open. You will read continuity on "Common" to "Start" or "Common" to "Run": Replace...
- Compressor will not start even though all components are good and all wires are connected. Compressor is locked up: replace. (This is not an electrical problem).
- Compressor sounds like it is running but does not pump refrigerant. Compressor is broken internally: replace. (This is not an electrical problem).
- Compressor (reciprocating) is going off on internal relief: (It will Scream/hiss like a "Banshee in a bear trap" You will hear it over 1/4 of a mile away. Very Very loud!!!!). Caused by excessive pressure due to a bad fan motor or over charge. All units should have a high pressure cutout. Shut it off immediately!!!
- Compressor has bad valves (reciprocating). It will hiss when running and pressure will equalize as soon as power is removed. Your compressor can run indefinitely like this but it is not efficient.
- Compressor Sings like a trumpet soon after being shut off (reciprocating). This is the pressure equalizing through the valves (quite loud). Do not worry as long as it doesn't hiss.
- Compressor has fallen off its mounts internally and sounds just like a fan motor with very bad bearings ( it sounds like a motorcycle in the parking lot). I even tried annother fan motor because I thought that is what it was. This system has been running for over a year like this. I am sure the neighbors don't like it much. Replace the compressor before it busts through the sides and releases a huge cloud of oil and refrigerant. Very rare!
- Fan motor will not run but will if pushed manually in either direction. Bad run capacitor or open "start winding".
- Fan motor will run for periods of time when unit is not calling. Motor is grounded.
- Fan motor will draw excessive current and shut off on winding protector. Bad windings. Motor may turn in one direction with run capacitor disconnected.
- Fan motor spins free but will "lock up" when energized. Thrust bearing is worn and motor is "pulling in" and bottoming out. Note: there will always be some end play in the shaft but too much will stop motor. If you are handy you can repair this.
- Fan motor makes loud noises. Bearings are bad you can replace the motor or if you are handy you may be able to swap parts from another motor.
- Fan motor makes a harmonious singing or rumbling sound. One or more rotor bars is broken or it is possible to get a combination of fan blade and motor that resonates (very loud!!!). Change something and it will go away. This is rare but does happen.
We service and repair the following brands:
American Standard, Amana, Arco, Arco-Aire, Bryant, Carrier, Coleman Evcon, Comfortmaker, Day/Night/Payne, Dunham-Bush, Fedders, Fredrich, Goodman, General Electric, Hotpoint, Heil, Intertherm, Janitrol, Kenmore, Lennox (Armstrong, Johnson Air-Ease), Miller, Modine, Nordyne, Rheem/Ruud, Sears, Stewart Warner, Trane, Williams, White-Westinghouse, Whirlpool, Weil Mclain, York, (Frasier Johnson/Borg Warner) and others.
Written By: Scott Meenen N3SJH of:
G&S MECHANICAL SERVICES.
Specializing in Mechanical, Controls and Electrical Modifications Of
Heating, Air-conditioning, Refrigeration, Cold storage,
Ice Production and Food preservation.
Anything having to do with Heat and Energy.
Serving MD, DC, and Northern VA.
Contact us by pager: 1-877-467-2914
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