AC fan won't start on 98~MB October 09, 2023, 02:14:13 pm Our AC fan will not start, it just makes a buzzing noise when using our generator, we do not have enough shore power to test it that way. I pulled the cover and the fan motor turns freely. I suspect the start capacitor? Any ideas? Karen~Liam 98 ~ MB NinA
Re: AC fan won't start on 98~MB Reply #1 – October 09, 2023, 03:30:38 pm Hi Liam; I agree with your diagnosis. There are actually two capacitors inside the one package. One to start/run the fan, and another one to start/run the compressor motor. I think Greg (Hilola) had this same issue recently. This was his thread: AC Not Working Somewhere around reply #47 and #49 was the resolution. RonB 2 Likes
Re: AC fan won't start on 98~MB Reply #2 – October 09, 2023, 05:43:15 pm If we purchased a soft start device, would that replace the starting capacitor? Karen~Liam 98 ~ MB NinA
Re: AC fan won't start on 98~MB Reply #3 – October 09, 2023, 07:18:10 pm Caution: these capacitors can hold dangerous electrical charges even after power has been removed. Be very careful, if changing or examining them. 1 Likes
Re: AC fan won't start on 98~MB Reply #4 – October 09, 2023, 07:33:25 pm “would that replace the starting capacitor?”Yes, installation disconnects the Start Cap, but retains the Run Cap.
Re: AC fan won't start on 98~MB Reply #5 – October 09, 2023, 07:38:20 pm Quote from: Karen & Liam - October 09, 2023, 05:43:15 pmIf we purchased a soft start device, would that replace the starting capacitor?The schematic below from SoftstartRV shows the standard Dometic wiring with the starting capacitor disconnected from the circuit so it can be removed. Dometic Wiring Diagrams and Instructions - SoftStartRVRemoving the starting capacitor creates no usable room, leaving the disconnected starting capacitor in place for a possible future soft-start failure isn't a bad idea. This would allow switching back to the original wiring and having an operational A/C.Larry 1 Likes
Re: AC fan won't start on 98~MB Reply #6 – October 09, 2023, 08:48:48 pm Thanks Larry, we may have a dead starting capacitor and there fore go with a soft start setup which would allow us to bypass the old non functioning capacitor but leave it in place for now.Andy, Thanks for the warning. Our plan would be to leave the old one in place and bypass with the new soft start unit. But definitely be careful with the rewiring and treat it as though it is live!Thanks Kieth alsoWe will probably have to do this on the road somewhere, our LD is out of its hanger and probably may not go back in before we leave. BTW PNW Weather has begun - Fall is here! Karen~Liam 98 ~ MB NinA
Re: AC fan won't start on 98~MB Reply #7 – October 10, 2023, 01:00:29 am Quote from: Karen & Liam - October 09, 2023, 08:48:48 pmThanks Larry, we may have a dead starting capacitor and there fore go with a soft start setup which would allow us to bypass the old non functioning capacitor but leave it in place for now.Your starting capacitor is probably OK, it's the Fan side of the double capacitor that is most likely bad.Larry
Re: AC fan won't start on 98~MB Reply #8 – October 10, 2023, 10:02:53 pm So it looks like a new combo start capacitor for our AC unit is around $7 to $16 on Amazon so I may first replace the old capacitor, then test the unit and then later get a soft start unit. We want to make sure our AC unit is working well before we upgrade to a soft start setup for it, after all it is 25 years old and we have only been exercising it a few times a year. We hope to be getting to warmer weather soon . . . Thanks for All of Your help! Karen~Liam 98 ~ MB NinA
Re: AC fan won't start on 98~MB Reply #9 – October 10, 2023, 11:44:49 pm Hi Liam; age and heat are the enemies of those start run capacitors. For a lightly used roof A/C unit, replacing the combined capacitor unit should return the air conditioner to 'good' working condition. Meanwhile I would be looking at the Houghton roof air which already has soft start circuitry built in, and in addition to being new, has a higher btuh rating. RonB 1 Likes
Re: AC fan won't start on 98~MB Reply #10 – October 15, 2023, 03:39:47 pm So I got a chance to check out the capacitor of our AC, looks like there are 2 capacitors a Philips 3530B2A0047A250A5 and a CSC 20+10UF/370VAC 60hz which I think is the fan motor start and compressor start capacitor? Replacement capacitor for the CSC is oval but should fit? I am not sure what the Philips capacitor is for?Karen~Liam 98 ~ MB NinA
Re: AC fan won't start on 98~MB Reply #11 – October 15, 2023, 07:24:13 pm The black plastic one is your start capacitor for the compressor, the other is the run capacitor for both the fan and compressor. At issue is most likely the run capacitor, keep all the specs as close to original as possible.Jon 1 Likes
Re: AC fan won't start on 98~MB Reply #12 – October 16, 2023, 12:23:14 pm Thanks Jon, I was able to find an oval one on Amazon with all of the exact values. There should be room but I may have to modify the the holding bracket. I will report back here with result probably later when I can get back on the roof in good weather here or when we are back on the road to climates with better weather. Karen~Liam 98 ~ MB NinA
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