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What is a wire lug in my AC unit?

I got this advice from Protek 480 and the live chat with another guru determined the loose wires are thermostat wires. Protek480: It sounds like a 120 volt line coming in from the pole. Red is the hot wire, white the common or neutral wire, and the green ground. Hook the red and white to the two main wire lugs in the unit and the green goes to the frame or ground lug that will tie to the frame. I don't know what a wire lug is or where the main and ground LUGS are or look like. Thanks a lot for any help!

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A lug is defined as a screw terminal made to accept one or more wires. Lugs as such are found in Circuit Breaker boxes (and on the circuit breakers themselves) Electrical junction boxes, Contactor relays such as found in Central Air units, those all being fairly large. There are also small lugs as would be associated with small wires such as thermostat wiring. Terminal diagrams for user-made connections are always provided with the unit being connected be it thermostat or HVAC unit. The thermostat comes with written documentation including diagrams, HVAC units typically have a diagram glued to the inside of the access panel.

Electricity can be your friend but can also kill you. Disconnect the power before altering or making any connections. If you don't know what you are doing, don't become a statistic, get help.

Posted on Jul 12, 2009


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Need to find out why my honeywell rht4650d thermostat is reading "in recovery"

The problem is likely with the cooling system, not the thermostat itself. Either the message from the thermostat is not being received by the AC unit, the solenoid isn't turning on the unit or it can't cool properly.
First check that none of the wires to the thermostat are loose or broken. You'll have to take the face plate off to check. The conductors are very small wires and can break easily. Depending on the unit,there are 4-5 wires usually for a HVAC system. If a wire is loose, reconnect it (push it in or screw it down gently). If a wire is broken, strip (for screw terminals) a new section and reconnect it. Check for ice build up on the condenser coils. (That is often a sign of a refrigerant leak. You'll need a professional to fix it and recharge the unit.)
Do you hear the fan running? If you do, then the condenser is a likely culprit. If the fan isn't running, then the control board for the system may be bad. You may want a professional to check the system. If you tell them the make and model, the technician can bring the parts if it is a problem with the control board.

I hope this helps.

Cindy Wells
(We had the broken wires to our thermostat in the winter. A few years ago, a nearby lightning strike had the AC off in the summer due to the control board damage. The house reached 90 degrees while we waited for the repair.)

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1 Answer

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1 Answer

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The outdoor AC contactor coil wire is usually yellow or blue, but you must make sure not to short the red wire to the other side of your transformer as that will cause you to have to buy a new transformer. Your unit wire diagram should show the wire to the AC contactor coil. You need to determine which wire feeds the AC coil which closes the contactor to the compressor and outdoor fan motor.

If this helps please rate me at

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1 Answer

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1 Answer

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Your Ruud is a 220 volt AC unit and requires two hot wires and one ground. The ground wire goes to the case inside of the electrical box close to the contactor that the two hot wires connect to. I have included a picture of what the grounding lug looks like so you will have no trouble finding it.

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