Question about Coleman Mach III Air Conditioner

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The compressor keeps running even though the thermostat is calling for it to shut-off and the blower has stopped. I think it may be a contactor sticking at the compressor. Just wondered if anybody else has had this problem?

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That's usually the problem, Shut the 230 volt power off to the outdoor unit and take the cover off of wire box and look in and see if the contactor is struck,you can also look at the points and they are usually melted and burnt.

Posted on Jun 09, 2009


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I have a Coleman Presidential II in my mobile home and it is summer time and I have my thermostat set to 76 and my unit keeps running even though my the temp is showing it is 72 in the house.

It could possibly be in the unit but my first guess would be in the tstat or the wire. If the compressor contactor was sticking the coil would freeze because I don't think the blower would continue to run. Check the wire near the unit for rodent damage or simply dry rotted. Therefore the wires are touching each other and not shutting off. Also be sure your tstat is not overshooting the set point because it is trying to get to your humidity set point. This is referred to as temperature droop. Also verify it does not have a minimum run time. Good luck

Jun 17, 2017 | Coleman Heating & Cooling


What to check when you air conditioner will not stop running:

If you discover that your outdoor air conditioner and/or heat pump runs continuously even with your thermostat off and the indoor blower is off, the most probable cause is a stuck contactor. In most residential air conditioners / heat pumps, the contactor is the switch that allows voltage to your compressor and condensor fan motor; therefore, allowing them to run. The contactor allows line voltage (normally 208 - 240 volts) to pass through a set a contacts to your motor. The contacts pull in when the thermostat calls for Cooling and they "open" when the thermostat "satisfies". This is accomplished with the use of a low voltage coil. When 24 volts is applied to the coil, it creates a magnetic force that pulls the contactor in to close the contacts. When the 24 volts is removed from the coil, the magnetic force no longer exists.....a spring will force the contacts back "open" and stop the compressor and fan motor from running.
The contactor is considered a wear-n-tear item as, eventually, the contacts will wear and begin to "pit". Eventually, they will either pit so severely, they will not allow enough voltage through them to operate the motors OR they may allow enough voltage and then overheat and weld themselves together. Often times you can lightly tap on the contactor and it will "free" the contacts and stop the motors. Unfortunately, once the contactor starts "sticking" it is highly likely it will stick again. Therefore, it is recommended that the contactor be replaced at first sign of sticking or when the contacts show signs of damage/overheating via a visual inspection.

Here's a video that might be helpful to you. :-)

on Apr 27, 2010 | Heating & Cooling

1 Answer

Intertherm MGHA-070ABFC-05 will not run/cool

Multiple problems. Eliminate thermostat first. Remove face from wall and turn on breaker. If fan still runs you have a bad board or bad relay. If fan outside is running compressor should be too. These operate on same contactor. Verify you are getting 24 volts to coil side of contactor. If odf stops working and contactor remains pulled in you have a bad motor. If odf motor stops working the compressor will shut off due to overheating.

Jun 07, 2016 | Intertherm Heating & Cooling

1 Answer

A/c won't stop running and no cool air

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

Aug 26, 2013 | Honeywell PRO 4000 5-2 Day Programmable...

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Central ac compressor keeps running

Sounds like the contactor is stuck. Turn the power off on both units and remove panel on condenser. Pull out on the contactor if engaged. Likely still needs replaced, it's going to happen again.

Jul 25, 2017 | Heating & Cooling

1 Answer

I have a Fredrich 8000btu wall unit model number CPO8F10 and the compressor will not shut off, even when the unit is turned off the compressor keeps running. the only way to shut it off is to unplug...

If your air conditioner or heat pump compressor won't shut off unless you pull the fuses or turn off the circuit breaker. You probably have a stuck contactor. The contactor is the name we give to the big relay that controls your air conditioner, heat pump or other large electrical device. 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. 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.

Aug 20, 2011 | Friedrich Heating & Cooling

1 Answer

Even I turn of the indoor unit via the controller , the outdoor unit is still running. I turn off the breaker and turn on still the the outdoor unit still running. What do you think the problem is?

Usually when this occurs it is a contactor burnt shut. If left to run, it will freeze the outdoor condensing unit into a block of ice. The contactor activates the compressor and
fan and the contactor is controlled by the low voltage from the thermostat. If the contact points are burnt shut the thermostat becomes of no use in controlling the outdoor condensing unit. The solution is to replace the contactor. Make sure all power to unit from all sources is shut off before attempting to replace. Hope this is helpful.

Jun 01, 2011 | Frigidaire Heating & Cooling

1 Answer

I turn on the Central A/C unit with the thermostat. The attic fan unit goes on and the system cools the house. When the system shuts down the fan unit shuts off but the outside compressor keeps running....

could be a thermostat problem but even more likely the contactor on the unit outside is stuck. In order to change this part you will have to get in to the outdoor unit. The contactor is the automatic switch that the thermostat energizes when the thermostat calls for aircond. The location of the contactor is in the outdoor unit (electrical section) and where the power will tie in to the unit. It is a little box looking part with terminals where most of the wiring connects. If the contacts are welded together the outside unit will not shut off. If you tempt to replace this part, make a diagram of all the wires connected to it before you take any of them off. Turn off all power to the outdoor unit before inspecting.

Apr 13, 2011 | Heating & Cooling

1 Answer

Possible Contactor Issue

Sounds like a bad fan switch in your unit. That unit has a fan board in it that is time delay on and off. Turn the fan to the on position and let it run all the time. If it keeps temp and does not shut off it is the fan realy board. The board also controls the compressor. Check that first and then the tsat. Russ

Jul 24, 2009 | Carrier 38CKC042 Air Conditioner

1 Answer

Coleman rv roof air conditioner

(1)Check compressor contactor or relay if it stock in the close position
(2)Check for welded contact points
(3)Check switch control for defect
(4) Check if compressor contactor still geting power when it is off

Let me know what works for you.

Mar 30, 2008 | Heating & Cooling

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