Question about Coleman Mach III Air Conditioner

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Just aquired a used mach 3 rooftop a/c for my tt. It was working last time previous owner used it. after install in tt, nothing comes on. there is power coming into thermostat and power running to the switch. I did notice the capacitor has been replaced before. any ideas? and yes the top unit is plugged into lower unit.

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  • dcsmsxxx Sep 08, 2010

    This unit is self contained. There is no saddle valve or any other valve to pump out freon. There is only the top unit that sits on top of the camper and the bottom (ceiling control unit) is inside the camper. I was with the individual that removed the unit from his enclosed trailer. He used a generator to power it. He says you only need 30 amps to run which is specifically the amperage running the camper. Incoming power has been checked, control switch has been checked, and thermostat control - all have power. I have noticed that the run capacitor has been replaced. According to the Model Mach 8333A871, the capacitor should be 25 mfd 370v. However, the one that is on it is 25mfd 440v. I do know that as long as the microfarad are the same that the volts can be higher. There is also a fan capacitor which has the correct part # on it. Neither look swelled or have an oil coming out of them. The run capacitor has a black dot on it between the terminals. I need to know how to discharge the capacitor(s) to be able to do any further testing that you feel needs to be performed.




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Hi, this one will be difficult to trouble shoot with out being there, but there are some things you can check. You say there is voltage to the thermostat? This sounds like a power problem, or the unit is off on a safety. You have power going to both the unit on top and the indoor unit? I believe this is what you are saying. When this unit was removed, was any freon lost that you know of? If the unit on top was not pumped down which I believe on this kind of system, they are not set up with a pump down valve to pump the freon from the outdoor unit to the outdoor receiver unit so the top unit can be removed, the problem is its off on its low pressure switch because it has no freon in the system at all. The freon has to be recovered to remove the condenser from the roof, and when installed on your roof, it has to be evacuated with a pump and recharged. If it has pump down valves on the high side line, this valve has to be closed off while the unit is running, and the compressor will pump the freon into the condensers receiver. After it is connected to your indoor coil, it has to be evacuated and the freon has to be released by opening up the liquid line valve to let the freon go through the system. Both the indoor and outdoor lines ( freon lines ) have to be connected and the air has to be removed by a vac. pump to make sure all air and non-condensables are removed before the freon is let loose or it is charged to spec's. Don't worry about the run capacitor. I strongly believe this unit has not a drop of freon in it and I don't believe it has a pump down valve on the compressor, so the last owner either bled the freon into the air, or it has a valve on the compressor that you can look for on the smaller of the 2 copper lines. If there is, you should have the unit evacuated before you open this valve. If you want to open it and take a chance on it, turn the valve in like you are closing it, its the opposite of a water valve and the unit will start if there is freon in it. You may want to call this guy to see what he did and if he did pump it down to save the freon. It has to go somewhere when the unit is split apart. I hope the best for you, but this is the problem, it will not come on due to no freon or its in the receiver. Call him and find out what he did. Please let me know what you find out. Please rate me as I know you will be kind, and I will be here to help in any way I can. Keep me posted on this.
A/C, Heating, & Refrigeration Contractor

Posted on Sep 08, 2010

  • 1 more comment 
  • Robert Horton
    Robert Horton Sep 08, 2010

    Hi, just checking in with you to see what you have found out.

  • Robert Horton
    Robert Horton Sep 09, 2010

    Hi I am sorry I have been at work and just found your comment. If the unit was running good with the generator at 30 amps, there is no problem with the freon. In fact, these units don't have to be pumped down or recovered as I was thinking of a residential unit at the time. As for the capacitors, just use a insulated screw driver to touch across the terminals and ground them out. You will hear them pop and see them arc if they are charged. Yes. you can go up in voltage from 370 to 440, but not on the microfareds. If this unit does not start up, there should only be 3- wires to connect if it is a 120 volt unit, Black, white and a bare ground into the j-box, and power cord to the indoor unit. If its 220 volts, not much difference. You may have a problem with the stat even though it has power. Just remove the cover and with the unit set to come on, take a piece of insulated wire and touch across the terminals of the wires on the stat, and if its faulty it will start. If nothing happens, put the cover on it.You can check the capacitors, but if the unit was running when you bought it, they will be fine. All you can doo, is make sure that all of the electrical is right, and the thermostat is working right, and it should run. Double check all of the power coming in where there is supposed to be, and the stat is what will bring it on. This may be your problem, even if it has power. Let me know what you find and we will get it going. It has to be a electrical problem, something tha'ts been over looked.. Keep me posted and I will check back more often now.

  • Robert Horton
    Robert Horton Sep 09, 2010

    When jumping out the thermostat, remove the cover and the sub-base to expose the wires. This is what you will jump and hold the wire on are the terminals to see if it starts. If it does, the stat is bad.



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