I have a 38ckc036750 A/C Unit and the fan run when the contactor closes but the compressor dont, the is a hard start capacitor that is across the run capacitor. what must I do to get the compressor going. thanks

There seems to be a problem with the wiring of the thermostat. Apparently the thermostat is calling for cool (if wired properly), but is not being satisfied. The thermostat is just a switch. When there's a call for cool, the thermostat sends 24-28 volts to the contactor (inside the condensing unit to start the compressor and outdoor fan). The indoor fan is energized through the fan relay (inside the air handler). When the temperature in the conditioned space reaches the set temperature,then the thermostat cuts the power to the contactor and it stops the compressor and outdoor fan. Check that the compressor is actually running, if not, check for 24-28 volts on the wires feeding the contactor, if there is, and the contactor isn't closing then the contactor is defective. If the contactor closes and the compressor doesn't come on, check the capacitor. If the capacitor is good then check your compressor motor. I suspect you have an improperly wired thermostat

Capacitors need to be matched. They are not interchangeable as the microfarad rating and voltage rating must be matched. Try to manually start the A/C without using the thermostat or remote and see what happens. Be careful with capacitors as they hold a charge when power is off. You have to disconnect power and take a screwdriver across the capacitor terminals to discharge the capacitor. make sure you are holding the insulated portion of the screwdriver when you do this. The microfarad rating and voltage are on the capacitor usually. This sounds more like a contactor problem which is controlled via a thermostat or remote. If you see a contactor in your troubleshooting efforts push it in and see if the compressor and fan start. If they do you have a control circuitry probllem. Again. push the contactor in while you are holding the insulated portion of of screwdriver or whatever you use to manually push the contactor closed with.

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sounds like a locked rotor, did the compressor get hot? did you check max amps on the compressor when it attempted to start?compressors have thermal protection built into their windings, a switch that will open to protect the compressor, and if the rotor is locked, normally you have to replace it, you could try putting what is called a start assist capacitor on it (AKA hard start kit) I would recommend the two wire model, easy to install.
You will need to wait for the thermal overload to reset, turn power off to unit till you get the kit on there.

Never ohmed a capacitor. But, your compressor should not need the start cap. Take it off completely and run machine. Not sure of your problem either but to ohm a compressor, common to start + common to run should = start to run. To test a capacitor without the capabilities of mfd on your meter measure the amps on the herm wire × 2650 = ?? Divide that by the volts across common and herm. This will give you the mfd rating. Same with fan amps × 2650 =?? ÷ volts = mfds. Remember, not the amps off the contactor...the amp reading on the cap wire. Good luck!!

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I assume that is a 240 volt unit. If you have a volt meter, check for power across the contactor . If it is a 240 volt unit you should get 240volts on both sides of the contactor. If you DO have voltage across the contactor (after it closes) you need to try and get to the compressor where the wires connect to it. There should also be 240 volts at the compressor terminals marked "C" and "R". If you have power at the compressor between C and R and the compressor is still not even trying to start, the compressor windings are open. Here is really what any tech will need to know to really help you:
(1) Is the fan motor running?
(2) what voltage is the unit?
(3) is the compressor humming or trying to start?
(4) do you have the proper voltage at the unit?

If you can answer these questions and you want to email me, do so and I will step you thru it. Be very careful , as you are dealing with high voltage.

Is the fan in the outdoor unit coming on? If it is, that narrows the problem to just the compressor or capacitor. If neither is running, check the disconnect or circuit breaker or fuses that are located close to the outside unit. If the unit has power, remove the cover where the power goes into the outside unit, set the thermostat to make the unit come on and see if the contactor is pulled in. If it is, use a meter to check for power on the load side of the contactor. If the fan is running, check the capacitor for the compressor. Most units use one that works both the fan and the compressor. If the capacitor looks swollen then it is bad, otherwise use a multimeter with the capacitor check function to test it. If the capacitor is good, check the compressor motor windings with the multimeter on the resistance function. Let me know what you find and I can give you more advice if this doesn't get you going.

I think you are talking about the outdoor unit so see if you can hear the compressor running. If it isn't running then set the thermostat so that the unit is not running and give the pressure time to come down.(15mins-30mins) Discharge pressure will build up if the fan isn't running and cause the compressor to shut down that's the reason for doing this. After this set the thermostat to call for a/c then see if the compressor is running. If it isn't first check your circuit breaker or disconnect or fuses. One of these should be located close to the outdoor unit. If you have power and it's not running then look at the contactor to see if it is pulled in. The contactor supplies both the fan and compressor. After that then check you capacitor. Some use a double capacitor that works the fan and the compressor. Let me know what you find

Can you tell if your outside unit is running (the fan and compressor)? Sometimes it is hard to hear the compressor for the fan. If they are running then you possibly have a low refrigerant charge and need to have some added. Refrigerant pressures and temps can be checked to verify this. If they are not running then you need to find out why. If both the fan and compressor are not running then first make sure all the breakers and disconnects are closed. Then a bad contactor or capacitor could be the problem. If its just the compressor that's not running then it could still be the capacitor or maybe the compressor.

Ok you have to trace the wires on down to what terminals they go to on the fan and especially the compressor. Usually you cant go by colors but always by the names on terminals and the like.

The capacitor has labels like (C or Com) (Fan or F) and (Comp or Herm). The compressor has terminals like (Com or C) (S or start) and (R or Run)

Write all the colors down on the compressor and the terminals that correspond to the colors.

Then do the same for what you can trace to the fan motor (usually there are only 1 or 2 going to the fan motor) If it just goes into the fan motor write down all the colors that go from the capacitor to the fan motor. The other wires from your description haven't been chewed or removed correct? If this answer is other than correct we have another step to perform.