Replace AC capacitor/install hard start 5-2-1 capacitor

Air conditioner fail.... ....


    Well few years later- our Dometic Brisk air II #B57915,13500 BTU failed to start. But starting at the beginning...Nothing better to do decided I needed to exercise the Generac generator and the Air conditioner. 2 hours later after replacing propane sensor batteries, then realizing propane tank empty (hadn't noted changeover valve was showing red when tank opened) and running to town to refill finally got gen started.

    Turned on AC, fan came on but compressor never kicked in. Seriously bogged down generator when trying, thought it was going to stall. I stopped the gen connected camper to shore and tried again. Fan starts but when compressor tried to start just got a loud hum. Let it set after a few tries then the fan wouldn't even come on.. Open inside cover verified connections, then removed outside cover. Lot of eyeballing determined has to be the start run capacitor. A common failure
    . NOTE-capacitor stores enough voltage to seriously hurt and can even kill. Turn off all power. Short the terminals with insulated tool between the terminals to drain off charge.

    Got on line and ordered replacement. If that's the issue its a $24 dollar fix. If not were done. As little as we actually use this hard to justify spending a lot to fix. However I did order at the same time a hard start 5-2-1 kit to help with the load, hopefully lower the huge amp draw at start up. A $34 upgrade (that's assuming the start run cap fixes).

    Just pictures of suspect capacitor. I didn't test, common failure. Our unit is dual cap, feeds motor and fan

    Numbers to find replacement- the 50/5 uF is the important one. Voltage at least what old unit is rated at. Mine is 370VAC. A 370/440VAC, more common or even a 440 will work. And then physical size. Lastly style, ours is a dual capacitor, one side for compressor, the other for fan.

    Just recording wire connections

    2 days later...

    Parts came in. Should be a few minutes to install replacement capacitor, verify AC works...rather hesitant as could very well be another issue so dragging my feets One problem is the capacitor was advertised at 2 3/8" diameter. It is 3". I'll set in AC to test but some modification to the box it mounts in required to install.

    Installing new start run cap (silver can on right) is just plugging it in. If it works then connect the hard start cap and its relay box (black/left)

    Staving off actually installing I shrink wrapped end of wires on the new 5-2-1 as all the terminals were exposed on the female connectors. Installing this will take a slight effort, finding location to mount, running a wire to the compressor common lead.

    No help for it, I ordered parts to up on the roof. I transferred AC wires to new capacitor and loosely set inside box. Want to see if this fixes before actually mounting

    WHOO WHHO! Success

    Temporally plugged in new cap to test. Turn on AC and fan started- then compressor kicked in. AC working! Stoked. Easy $24 fix. So I'll go ahead and install it and add the new hard start 5-2-1 cap. Removed the box from AC to modify in shop and pre-mount components.


    Few gotchas, the new cap is full 3" in diameter, old one was 2". It will with some effort & new hard start cap, mount in the 'box' but doesn't allow room for the new hard start relay. If I had some sheet metal easily make a bigger box but I dont.

    Looking at it though the box bottom is partially open. If I cut/fold the 'shelf' replacement cap could set lower it would give room for relay. Id really like all this contained to the box so out comes the snips and hammer

    Folded the 'shelf; down, cut off about 1/2". Cut where wires will pass and folded edges over so wires wont see sharp edges. The relay box has small tit on back so drilled a hole for it. This will help keep it at height. Flattened back so larger replacement cap will fit.

    Drilled holes to fasten caps and relay with zip ties. Didn't have any 1/4" female connectors so looped the wires for now. Way to long. I'll revisit and shorten the red and yellow wires. The replacement can on right to be zip tied once back in AC, left loose so I can plug in AC wires.

    And installed. Tight but works. I was going to use metal strap but its tight enough once cover on nothing is going to move. Zip ties dont really do much.

    There is a black lead from the 5-2-1 relay that connects to the compressor common lead. On many ACs this connection is on a terminal of contactor switch. This Dometic doest have one so I need to extend black wire, run over and tie to the blue common wire from compressor.

    FYI, next few pics because this, finding identifying correct wire to tap, was in my opinion the most unclear.

    Finding the common wire from compressor. Remove the wiring terminal cap from top of compressor. Identify color of common wire, mine is blue. Lift off the AC black foam cover, this wire will exit compressor via loom and run into the foam box (the other 2 compressor wires, mine are red & white, run over to capacitor metal box)

    Not mine but shows common wire on compressor and running into foam box.

    I routed extended black wire form new 5-2-1 following existing wires across to other side of AC where blue wire from compressor is inside of foam box. Cut blue wire, solder back together with new black wire.

    Then with more than a little hesitation plugged camper back into shore power. Turned on the AC fan and went to roof to make sure no magic smoke rolling out. Went back inside, turned to max cool, , hmm didn't hear compressor kick on. Went back to roof-still no smoke. Went back inside, AC is blasting Cold air. Turned off cold, no audible difference? Waited a few minuets and turn back to max cool. Still cant hear compressor coming on but air turned cold within seconds.

    Odd, this AC when compressor kicked on was always with a loud thud and slight slow down of fan. I have no way to test load or amp pull, I can only assume its a function of the new start capacitor and the addition of the 5-2-1 hard start cap. So far impressed, fixed and upgraded. Tomorrow Ill run again but on the generator. I know how gen reacts to the load, be nice to hear it not bog as hard as it use to when compressor kicks on. But that may be wishful thinking, but hopefully not as huge a load when AC kicks in.

    Finally tested on generator.
    Simply amazed. Start gen let it run couple of minuets. Turn on fan, gen slightly increases rpm.
    Then turn to cool. Generator again briefly loads, I mean half a second and its up to full RPM. Wow. Before, when compressor kicked in it struggled for maybe 5 seconds before ramping up. So initial load IS considerably less. Generator getting up to speed all but instantaneous now.
    I turned off the cool, gen slows down and then quickly turned back to full cool (which shouldn't do that). Gen didn't like that and quickly turned off cool. Let it run for minute on fan, turn back to cool, instant ramp up.

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