If the indoor blower fan will not shut off either then the problem is NOT the contactor in the outdoor unit but a problem with the thermostat or the wiring to it either at the subbase or the furnace. Before replacing your thermostat you should isolate the cause of the problem or it will persist and drive you nuts. Look for wires touching or cut too long.
A contactor or relay is an electrical device that takes a control signal usually 12 volts DC, 24, 120, 208-230 volts ac and creates a magnetic field to pull in a set of contacts that controls another device that may or may not get its electrical power from the same circuit. Note: 99% of most control circuits are 24 volts AC.
The contactor has steel contacts that are plated with silver. When the silver wears away you have just plain steel and the steel will weld itself together. Sometimes if you whack the contactor with a screw driver you may free it for a while but the problem will re occur. This problem is especially a problem when a piece of equipment has not been run for a period of time.
It is normal for the contactor to wear out over time like brake pads on a car. If the contactor shows any signs of wear it should be replaced as a preventative measure or as part of maintenance.
If you suspect a stuck contactor a 100% accurate test is to turn off the power to the indoor section which removes control voltage to the outdoor section and it (outdoor section) keeps running. Do not keep messing with it, your contactor it is bad and you will destroy your compressor if you let it run!!!
You can also have problems with spiders building nests in the contactor; the silk is an insulator and will prevent electricity from flowing.
Replacing a contactor is a simple matter
and they are readily available. We will ship you one if you ask.
Costs vary from about $40 installed to several
hundred dollars depending on the size and current carrying capacity.
If your compressor does not shut off when it needs to and the indoor fan does you will destroy your compressor. The high and low pressure cut-outs won't work either.
Some heat pump systems use two run capacitors (total of 3 if you include the fan) instead of a crankcase heater for the compressor (GE, Rheem/Ruud and others). It is possible for the contactor to fail where the compressor or the fan will run but not the other. When replacing a contactor on a system like this be extremely careful to get the wiring correct or the compressor may be damaged.
Contactors are also used in motor starters. Brand names include Allen Bradley, Cutler Hammer, Telemecanique, Furnas, Honeywell, General Electric (Mars), Robertshaw, White Rodgers, Steveco, ITT and others.
Used on the following brands: American
Standard, Amana, Arco, Arco-Air, Bryant, Carrier, Coleman Evcon, Comfortmaker,
Day/Night/Payne, Dunham-Bush, Fedders, Fredrich, Fraser Johnson, 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.
To send us a question about your unit
please use our cooling Fill
Out Form.
For general heating questions please
use this form
Image of 2 pole contactor and Sperry Digisnap Clamp on
ammeter, available at Lowes for about $80.
The "non contact volts feature" is worth the price.
Image of 1 pole contactor (Honeywell and another brand).
Contactors can have as may as 4 poles. Most single phase contactors have
2 poles and three phase contactors will have 3 poles plus some auxiliary
contacts. These are common items that can be ordered from any supply house.
Do not try to order one by part number or an exact replacement. In most
cases a 30 amp two pole contactor with a 24 volt coil will be correct.
Final Warning:
Do not try to clean or repair a contactor,
if you have then stop and turn the power off to the equipment. Once the
silver erodes all you have is plain steel and it will weld closed destroying
your equipment and possibly starting a fire!!!. Unless you have an
industrial contactor that costs hundreds of dollars that can be repaired,
the only solution it to replace the contactor.
This text written by: Scott Meenen * G & S MechanicalWritten 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.
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