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HVAC, Air Conditioners, Aqua Hot, Primus, Webasto, Chassis Heaters, Furnaces and Water Heaters Questions and information about the wide variety of Heating and Air Conditioning as well as Water Heater systems available are discussed here. |
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This info applies to Dometic roof mounted air conditioner model 600315.421. These are the original roof airs on my 1997 coach. Yours may differ so be certain you confirm part numbers before replacing anything.
Why did I replace these parts? I recently noticed that both the rear A/C fan and compressor were taking longer than usual to start and were a bit noisier. The first (and least expensive) place to start was the capacitors. Each A/C uses a Start Capacitor, a Run Capacitor and a PTCR (thermistor) device. The date codes on my parts were telling me that they were probably original (or very close to it). Capacitors don't last forever - they degrade over time. A weak cap causes the device it's supporting (in this case either the fan or compressor) to work harder. Given enough time, a weak cap can lead to premature fan failure or, even worse, compressor failure. The new parts I used: Start Capacitor: MARS p/n 11963 (108-130 MFD, 330 VAC) Run Capacitor: MARS p/n 12713 (25 + 10.0 MFD, 370 VAC) PTCR Device: Cera-Mite p/n 305C20 (35 Ohm), Dometic p/n 3100876.006 Dometic service manual specifies the following: Start Capacitor: Dometic p/n 3100236.219 (88-106 MFD, 250 VAC) Run Capacitor: Dometic p/n 3100248.453 (25 + 10.0 MFD, 370 VAC) PTCR Device: Dometic p/n 3310731.009 (35 Ohm) To assist the older compressor upon start-up I chose to use a slightly larger (+22.7%) Start Cap. I spoke with Tecumseh (A/C compressor manufacturer) tech support and was told that using a larger Start Cap (~20%) was ok. The Run Cap and the PTCR device I used are the exact specs that Dometic recommends. You don't have to use Dometic parts. In fact, you'll save yourself some money by choosing an equivalent replacement that's not a Dometic (i.e., 3310... or 3100...) part number. For the Start and Run Caps I chose to go with parts made by MARS. However, the PTCR device I used is a Dometic part number. It's very easy to replace these parts. Make sure you first disconnect power from the air conditioner. After that just remove the A/C shroud, remove the capacitor cover plate, and replace the capacitors and PTCR. If you move slow like me, by the time you get to the roof, remove the covers and gain access to the caps, any voltage will most likely have dissipated. But you might check with a voltmeter just to be safe. And while you're up there with the shroud removed, it might be a good time to clean and inspect the entire roof A/C unit. After replacing these parts and putting it back together I noticed a decrease in both the fan and compressor start-up times and less noise overall.
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Kevin & Kerry 1997 WLWB 43' "BB Belle" 2005 Jeep Liberty Limited 4x4 Last edited by Kev; 08-18-2018 at 08:01 PM. |
#2
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Excellent info Kev.
For those curious about his front A/C, we have both installed Micro-Air’s Easy Start module (see posts 26-30 HERE). This unit replaces the capacitors and smooths compressor startup, allowing an inverter to power ones AC without using the generator. However that black box isn’t cheap, so on my rear AC a stronger soft capacitor works just fine.
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Van & Toni in TX & AZ 2004 M380 DS & 2013 Fiat 500 Pop or 2021 Jeep JL |
#3
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My center AC quit. Was ready to replace, but decided to try replacing the capacitors. Works just fine now!
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Melvin and Charlene Pierce Scranton, ND "Smoke N Mirrors" Royale Conversion 1990 PT40WB |
#4
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I would be reluctant to pay $300 for a magic start box. There is nothing magic about a start device. There are only a couple of ways you can engage and disengage a start capacitor. PTC or potential relay.
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Mallie & Karen Lennon Eufaula, Oklahoma 95 42' Wanderlodge Please use e mail instead of Private Message Mallie@EuLake.com |
#5
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Are you referring to a Microair starter? If so you couldn't be more wrong.
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#6
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this is not what you think it is more like freq. drive as it lowers inrush amp i am not sure of what all is involved but they are the real deal i would think they play with voltage as well as current.. if i ever get one i will figure it out.. but as of now i don't know its magic!! mike
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mike mcgraugh 2003 LXI "Blacktop Gyspy" even a blind squirrel finds a nut once in awhile washington Il. |
#7
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Its pure magic until you guys figure it out,as far as i'm concerned.
Myself,i stick with the old school stuff,caps are fun! I will bring one to my seminar,will it be charged?or not?
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DO NOT SEND PM email me at randy@randydupree.com only. Randy Dupree 2000 LXI 43 Bainbridge,Ga. Port St Joe Fl. www.buybyebluebird.com randy@randydupree.com |
#8
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Mallie & Karen Lennon Eufaula, Oklahoma 95 42' Wanderlodge Please use e mail instead of Private Message Mallie@EuLake.com |
#9
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Who are you going to try it on? I won't be near you during that show and tell. ![]() ![]()
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JOHN FINN FORUM MODERATOR-ADMINISTRATOR 1982 FC35RB I'm NO EXPERT, but I did stay in the FINN'S INN EXPRESS last night HOPKINS, SOUTH CAROLINA VISIT THE FINN'S INN EXPRESS REMODELING ADVENTURE AND TECH. TIPS I'M SO SLOW ON THE HILLS,THAT I GET TO SMELL THE FLOWERS AS I GO BY.....AND WATCH THEM GROW TOO!! NOT SO MUCH ANYMORE ![]() ![]() Visit the WILD HARE RACING website REMEMBER 9/11 |
#10
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i think they are all charged - until ya check-um...been to may radio/ham swap meets!!
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mike mcgraugh 2003 LXI "Blacktop Gyspy" even a blind squirrel finds a nut once in awhile washington Il. |
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