Duo-Therm AC not cooling Hi, we have a Dometic Duo-Therm 59516.531 ac on our 2003 Sunseeker that has quit cooling. It worked fine on Sunday, but didn't on Monday. The fan runs normally but the compressor is not working at all - it doesn't try to start or make any sound at all. I live 160 miles from the nearest dometic approved service center so would like to try to fix it myself if possible. I suspect that the compressor delay circuit board might be bad, but don't know how to tell for sure. I have confirmed that 120 vac is coming into the circuit board. I do hear a click in the black plastic delay component after 150 seconds, but there is zero voltage on the output lug when all wires are connected. However, if I disconnect the wire from the output lug that goes to the compressor, then I measure 120 vac on the output lug both before and after the 150 second delay. That has me confused and makes me wonder if one of the capacitors is bad or if the compressor itself is bad. Are there any measurements I can make with a basic multi-meter that would indicate exactly what component is bad?

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05 Mar, 2017

  • 79%
    Solved this issue
  • 103min
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  • 61%
    Recommend to DIY
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If the unit is a 220v, you will see 110v on that unplugged wire you mentioned. If it is 110v system then you probably have a swollen or open capacitor. The lil black box on the control board is a micro relay. And they do act up in different ways. If it's clicking, normally, that tells me its working. If it's 220v, make sure you have 220v to the system. If you have 220v to the system, and no power goilg through the micro relay, you can try jumping by that relay. While it's plugged into the relay (both wires), touch the 2 wire ends together with the end of a screwdriver for a second or 2 and listen for the comp to start. If it does you found your problem. All this does is bypass the relay by connecting those wire together. I've seen these units not work, if there is 2 units on the roof, due to a safety that doesn't allow both to operate at the same time, and never found the reason why. Now if it's 110v, you'll need to dig a bit more, following your voltage. Source, line, load. The source volts enter, the line feeds to the switch(s), the load is the motor/comp. The capacitor is a round/oval metal cylinder with wires attached, and stores voltage so it must be discharged by shorting the terminals to each other or ground. POWER OFF FIRST! Be safe please. If its 220v and you only have 110, check the breaker(s). If the capacitor is swollen up on top, where the wires connect, or have this sticky oil coming out of it, it's damaged. More that likely its the board. Last 1 changed was $129 my cost, not the customers. And I had to rewire the unit a bit and change the tstat also. So if you end up buying a board, ask them about an exact replacement. If it's not, ask them if they can draw you a schematic to help. Hope this helps!
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