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Old 02-03-2013, 09:46 AM   #1
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Hard Start Capacitor for 13,500 BTU AC Unit

Someone recently asked about a hard start capacitor for their 13,500 AC unit. I shopped for one some weeks ago and ended up buying one from a local RV dealer, but I haven’t installed it yet. I will after the snow melts.

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If you open the link http://www.rvcomfort.com/rvp/pdf_doc...literature.pdf and scroll down you will see the Mach 3 13,500 AC draws 15.3 amps for cooling, so it can run safely on a 20 amp circuit. (16 amps for heating – if equipped). But when you first turn it on it draws much higher, (my model is rated to draw 33 amps) but only for a split-second, it’s called “in-rush”. That’s common to air compressors. It’s kind of like rolling a heavy object – hard to get moving, but easier once it’s going.

So your 20 amp circuit needs to be protected from the high in-rush current. That’s usually accomplished by a delay fuse or breaker. The in-rush current won’t blow the fuse or trip the breaker because it’s manufactured not to, and the rest of the circuit is not damaged because it happens so fast.

If you are plugged into a source that can handle the bigger draw such as residential, campground, or commercial outlets, you don’t need to concern yourself with in-rush. If you are using a generator, it’s important to know it has sufficient power to supply the in-rush current. Portable generators will fail sooner-or-later when asked to provide more power than they are rated for – even momentarily.

There is no formula I’m aware of to determine what your draw will be after installing a hard start capacitor. For the model I have, it’s commonly thought to be “less than 20 amps”. I’m going to have mine checked with a clamp meter before buying a generator.

The hard start capacitor comes as a kit, and includes the capacitor, wires, PTCR switch, instructions, and a strap clamp. (The PTCR removes the capacitor from the circuit after the AC has started. In the picture, it’s already connected to the top of the capacitor.) When installed, the capacitor stands next to the “compressor run” capacitor and also connects to it. It’s held in place with the strap. The compressor run capacitor is equipped with electrical connections on its terminals to connect the hard start capacitor. You already have a strap holding your compressor and fan capacitors, so it might just need an adjustment. That’s a long way of saying take the cover off, set it in place, and plug it in.

Check first, because you might not need one. I found out there are about 20 different models in the 48000 series. Some models come equipped with a hard start capacitor.

I hope you all appreciate this. It’s a lot for a fat-fingered old man that can’t type.

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Old 02-15-2014, 06:15 PM   #2
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Great information and write-up, thanks for posting.




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Old 02-15-2014, 06:42 PM   #3
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And they do work. My 2007 fleetwood had a 13,500 A/c unit, and when trying to start on my 3000w Genset, it would frequently overload and trip. I added a hard start capacitor ( I think I paid about $50 ?), and it did the trick.

Very easy to install - just make sure the other capacitors in line have discharged before you go play around in there.
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Old 02-16-2014, 12:17 PM   #4
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The SUPCO SPP6 (not the SPP6E) is what many RV A/C owners install in their units for generator use.

I snipped this from another post from ModMyRV:

If you are adding a hardstart to your RV A/C unit, use the SPP6 [no E]. The SPP6E is not designed for 120VAC applications, The “E” series is also an instant restart unit, this does not allow the generator sufficient time to rampup to full power. The SPP6 has the preferred PTC relay and allows a longer ramp up time. The SPP6 is rated for 120VAC usage.
Remember for every thousand feet above sea level you generator drops 3% of output. On hotter days the A/C drops in efficiency as well. Check with your A/C manufacturer on the correct generator size for your unit. As far as I know there is not a manufacturer that will recommend a 2000 watt generator to run a 13,500 BTU A/C unit.
If you have any questions about the SPP6 or any other Supco part, please contact us at 1-800-333-9125 ext. 261 our Tech Support will be glad to assist you.
Jim Berry
Director Product Management
Sealed Unit Parts Co., Inc.
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Old 02-16-2014, 08:26 PM   #5
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when you buy a hard start kit for the capacitor,be carefull, they can take out the comp.if its not a good hard start.. when installing hard start to run capacitor,make sure you discharge the run cap, it can shock you. just looking out for you. I'm a hvac mechanic.
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Old 02-16-2014, 09:24 PM   #6
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I have been running a SUPCO SPP6E (did plenty of research before I installed it) for 2 years now and it allows me to run my 3k honda in eco mode and the A/C can cycle on and off no problem. Before it was installed the A/C would still cycle but it really bogged down the genny.
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Old 02-17-2014, 04:28 AM   #7
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I've read others have used the 'E' flavored SPP6 with success. I wonder why SUPCO recommends the straight up SPP6 version instead?

***Browsing to Airxcel (for a Mach3 Plus A/C electrical review) and SUPCO's website gives me this the following:***

Under the FAQ for the Airexcel, you can find a question asking for the proper operating VAC (voltage) and they give this answer: Proper operating voltage is 115.0 VAC. The unit may be run safely between 103.5 volts and 126.5 volts. Do not operate the air conditioner outside of these parameters, as serious component damage may result.

So lets go to SUPCO and get some specs.

For the SPP6E they offer:

Capacitor size (F): 88-106
Recommended Range (hp): 1/2 - 3
Operating Voltage(VAC): 170-277

For the SPP6 they offer:
Capacitor size (F): 130-156
Recommended Range (hp): 1 - 10 hp
Operating Voltage VAC: 90-277

It seems to me that the regular SPP6 is the one we should be using for our RV A/Cs. Now, I have read some have had success w/ the other one, but I'll be putting the regular SPP6 in mine.

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