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We're changing a compressor and want to see relationship between the capacitor contactor and other things

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The capacitor aids a unit in starting and then in running.

the contactor is a switch that tells the compressor when to come on. It is usually controlled by another voltage. So the low voltage control circuit powers a coil in the contactor, which in turn, energizes the contactor, thus closing the contacts to turn on the compressor.

Posted on Jul 06, 2010


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The air coming from the air conditioner is not cold

First, power everything down! You will need to climb on top and remove the cover. Inside you will see the compressor, condenser grill, a contactor-relay and capacitor. Most likely it is either the capacitor or contactor-relay (70% probability) or the compressor (25%). If you see ice build up on the connections or on the condenser grill it could be that you are low on freon or have a leak in your sealed system.

If things look normal then I would go with the contactor-relay and capacitor. If things are iced up, you will need trained technician help. Most AC shops will work on it, but won't have the Dometic parts. An RV place will have the parts but you usually pay a premium price for the labor and service.

Aug 18, 2011 | Dometic Rooftop RV Air Conditioner


Wiring up a compressor + start kit

Wiring up a compressor
If there is an identifying mark on one side of the capacitor such as a Dash, Red paint or arrow pointing one direction that will be the run side of the capacitor, if no marks you can use either side for start or run.
If you have three terminals on the capacitor you have a dual capacitor, (C = RUN compressor and fan) (HERM = compressor start) and (FAN is fan start wire).
The Start wire goes to one side of the run capacitor it will be the only wire on that side of the capacitor.
The Run wire goes to the terminal side (T2) of the contactor, it will have another
wire from that terminal to the run capacitor which is the opposite side of the start wire.
The Common wire will go to the other side of the contactor (T1).
Start Kit
Start from the capacitor to terminal #1 on start relay There should be another wire from
here to start on the compressor.
Common from contactor (T1) to terminal #5 on start relay. There should be a wire from this terminal to the Common terminal on the compressor.(there will not be a capacitor in this circuit)
Run from the other side of the contactor (T2) to the start capacitor and from the other
Side of the start capacitor to terminal #2 on the start relay. There should also be a wire from this
Terminal to Run on the compressor.

on Jan 24, 2010 | Heating & Cooling

1 Answer

I changed out the capacitor in my outdoor AC unit and it still won't work. There is a slight humming noise and I can see the contactor pull in and out when the thermostat turns it on. Could my fan...

I would start by inspecting the contactor make sure you are getting full voltage thru it to your fan and compressor. Usually there is a capacitor for the fan and one for the compressor. Make sure they are getting proper power and that capacitors are good. check amp draw and go from there,

Jun 24, 2011 | Heating & Cooling

2 Answers

Compresor not coming on, have installed new hard start capacitor, only 1.2 volts at compressor

You must not have both sides of power going to the unit. I will try to tell you how that unit is wired. I don't know what kind of hard start kit you have. If it is just a two wire start capacitor kit, you need to connect it to "herm" and "C" on the capacitor.

"C" from compressor will go to the contactor
"R" from compressor will go to "C" on the capacitor
"S" form compressor will go to "herm" on capacitor

note: "R" on compressor will go to "C" on capacitor with a jumper wire from the capacitor to the other side of the contactor.

Jun 22, 2011 | Coleman Heating & Cooling

1 Answer

Outside fan motor will not start. will this keep compressor from operating?

Is the compressor running? First check your contactor and see if it is pulled in energizing the fan and compressor. If it is then check the voltage at the load side of the contactor. If you don't have voltage at the contactor then check you breakers or fuses. If the contactor is pulled in and you have voltage then check the capacitor for the fan and compressor and replace if it is bad. If your compressor is running and the fan isn't it will cause you compressor to shut down because of high pressure. If the compressor is running and the fan isn't then again check the capacitor and replace it if it's bad.

May 22, 2010 | Goodman CKL24AR24 Air Conditioner

1 Answer

My model ACD2234HRQ is approx 90 days out of

you need to replace the rtc overload contactor located on the compressor body,there is also a run capacitor on the contactor,replace this along with the rtc contactor,this is your problem,the contactor and overload give the compressor starting power and run power to the windings,if the capacitor is bad it doesnt have enough torque to overcome the power to turn the compressor initially

Mar 13, 2010 | Amana 22.6 cu. ft. Side-By-Side...

1 Answer

The motor does not turn and air conditioner does not turn on

if you are talking about the outside condensing have to check the contactor to make sure your unit is being called for. the second thing is the capacitor. if your fan and your compressor don't come on it is either the contactor or the capacitor.

Aug 09, 2009 | Bryant Heating & Cooling

1 Answer

Air conditioner does not work. I turn it on and it tries to start, will not start, turns off. When I turn the thermostat off you can hear a click back by the A/C unit. This is on an 03 Weekend Warrior...

the click you hear is possibly the contactor switch on the unit. This swith is activated by the thermostat which in turn sends voltage to the compressor. First things first, You need to check the contactor swith to insure you are getting power from the switch on.. Activate the thermostat the contactor will activate you shoud get the same voltage reading from l-1 and l-2 as you get from the t-1 t-2 sides of the contactor. if these readings carry the same volts then your problem is towards the compressor. Next item to check is the capacitor. this is a round or oval shaped metal cylinder that has several wires going to it, Some of these capacitors are dual, in other words they run both compressor and condensator fan motor in one unit sometimes each peice , compressor, fan motor, has a seperate capacitors If it is a dual capacitor the will be 4 or more wires going to it. since these aren't as costly I would recommend that you replace the capacitor and see if that has cured your problem., If it hasn't then you are possibly looking at a bad compressor and an a/c tech would need to be called to check that for you. Good Luck


Jul 17, 2009 | Dometic Rooftop RV Air Conditioner

1 Answer

Just had to replace contactor on a/c unit-split system.Unit is running-compressor nor kicking in-no cold air

Is the compressor trying to run. Make sure wires to capacitor or on the contactor correctly. Most of the time there is a red wire going to capacitor common tap C. The other wire on the same terminal goes to compressor. The other side of the contactor is the black wire to common on compressor. You might have terminal burnt off on your compressor Very simple repair. Let me know make and model and I can tell you more.

Jun 12, 2009 | Heating & Cooling

2 Answers

I have a ruud model number upne 060 jbz the compressor is not coming on .could it be the capacitor?

It could be, could also be lots of other things. Is the indoor fan comming on? do you have 240 volts at the contactor? both sides of the contactor? Is the contactor pulling in? Is there 24 volts on the low voltage side of the contactor? is there voltage at the compresser? Did you ohm out the windings?

Apr 12, 2009 | Heating & Cooling

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