Hard Start Capacitors

Desert185 · 03-26-2016, 12:32 PM

Are these capacitors brand dependent or can I buy whatever is available to install one on each of my two Dometics (15 and 13.5)?

Thx

Bob Landry · 03-26-2016, 03:36 PM

Why do you think both of your units need hard start kits? If your units are starting hard because of inadequate power, they won't do anything for you.

dcg9381 · 03-26-2016, 03:37 PM

Capacitors are matched to motors, so I'm not sure that I'd out and just start messing with capacitor ratings. Get something made for your AC unit.

**JRTJH** · 03-26-2016, 09:13 PM

Good advice from Bob Landry and dcg9381. If your A/C's are starting "OK" as is, a hard start capacitor won't help. If they are bogging down on shore power and occasionally tripping a breaker, then adding the kit would probably help.

Each Dometic A/C model has a specific "hard start capacitor kit". The capacitor is matched to the compressor and is wired for a simple "plug and play" installation. I'm sure a HVAC repairman would "rig something" to fit your system, but chances are that it would cost more than the $25 or so the kit will cost you from Amazon or Camping World.

It's been my experience that if you're trying to get an A/C to run on "minimal generator power" and it's tripping the generator breaker, installing the kit won't help. You should be "good to go" with your two "smart tools" generators running them with a parallel cable. (for one A/C) but you'd be pushing your luck trying to run two A/C's with that generator system. It may work in cooler weather, and it may work for a while in warmer weather, but it's a heck of a load on your generators to power two rooftop units.

Bob Landry · 03-27-2016, 05:07 AM

Actually the SUPP6 is the generic one used for just about all of the RV AC compressors when needed. That said, the systems are designed with the appropriate start components and come that way from the factory. In the event of a start capacitor failure it's better to replace it with one of original value. There are some units that do not use start capacitors but use a different start assist device, I forget the acronym for it.
The only reason for a hard stat kit is if the compressor must overcome high head pressure at start up. This happens a lot in units that use an expansion valve, but rarely in RV type units that use a capillary tube to meter refrigerant into the evaporator. As soon as the AC turns off, the pressures equalize in around 30 seconds. Another reason for use is if the compressor is trying to start using inadequate voltage in which case that issue needs to be corrected.
Bottom line... More is not always better and if it ain't broke, don't fix it.

Desert185 · 03-27-2016, 10:26 AM

Quote:

Originally Posted by JRTJH

Good advice from Bob Landry and dcg9381. If your A/C's are starting "OK" as is, a hard start capacitor won't help. If they are bogging down on shore power and occasionally tripping a breaker, then adding the kit would probably help.

Each Dometic A/C model has a specific "hard start capacitor kit". The capacitor is matched to the compressor and is wired for a simple "plug and play" installation. I'm sure a HVAC repairman would "rig something" to fit your system, but chances are that it would cost more than the $25 or so the kit will cost you from Amazon or Camping World.

It's been my experience that if you're trying to get an A/C to run on "minimal generator power" and it's tripping the generator breaker, installing the kit won't help. You should be "good to go" with your two "smart tools" generators running them with a parallel cable. (for one A/C) but you'd be pushing your luck trying to run two A/C's with that generator system. It may work in cooler weather, and it may work for a while in warmer weather, but it's a heck of a load on your generators to power two rooftop units.

I haven't tried to run both AC's on the gen's in parallel, but I run one occasionally under hot and high conditions. I thought a hard start capacitor would help the process when the gen's are at 7,000'+. I've a trip coming up at the end of April, but it will still be cool enough to not need the AC at that high location. I was just reverting to my Boy Scout training, even though I do subscribe to the "if it ain't broke..." policy.

Appreciate the info.

Desert185 · 03-27-2016, 10:28 AM

Quote:

Originally Posted by dcg9381

Capacitors are matched to motors, so I'm not sure that I'd out and just start messing with capacitor ratings. Get something made for your AC unit.

That's why I was asking the question.

**JRTJH** · 03-27-2016, 10:44 AM

Quote:

Originally Posted by Desert185

I haven't tried to run both AC's on the gen's in parallel, but I run one occasionally under hot and high conditions. I thought a hard start capacitor would help the process when the gen's are at 7,000'+. I've a trip coming up at the end of April, but it will still be cool enough to not need the AC at that high location. I was just reverting to my Boy Scout training, even though I do subscribe to the "if it ain't broke..." policy.

Appreciate the info.

I think you'd just be spending money on EZ start kits, that could be better used to buy adult beverages for consumption under the awning.....

Desert185 · 03-27-2016, 10:57 AM

Quote:

Originally Posted by JRTJH

I think you'd just be spending money on EZ start kits, that could be better used to buy adult beverages for consumption under the awning.....

Adult beverages are already in the budget.

I press on without the hard start's and see what develops. Thanks.

Bob Landry · 03-27-2016, 11:00 AM

Not sure what constitutes a "high" condition. If it's altitude, it is irrelevant as the compressor and refrigerant circuit is a sealed system and is unaffected by temp, altitude, or humidity.

A correctly charged rooftop AC will draw it's stated running amperage at 95 degrees outside ambient temp. For every 10 degree change in ambient temp, the current draw of the compressor changes by one amp.

For example, a compressor that draws 14A @ 95 degrees will draw 15A @ 105 degrees and 13.5A @ 90 degrees measured with clamp on meter. This is how you can tell if a system is correctly charged without having to tap into it for gauges.
Ambient temperature only affects running amp draw and has nothing to do with startup.

Desert185 · 03-27-2016, 01:18 PM

Quote:

Originally Posted by Bob Landry

Not sure what constitutes a "high" condition. If it's altitude, it is irrelevant as the compressor and refrigerant circuit is a sealed system and is unaffected by temp, altitude, or humidity.

A correctly charged rooftop AC will draw it's stated running amperage at 95 degrees outside ambient temp. For every 10 degree change in ambient temp, the current draw of the compressor changes by one amp.

For example, a compressor that draws 14A @ 95 degrees will draw 15A @ 105 degrees and 13.5A @ 90 degrees measured with clamp on meter. This is how you can tell if a system is correctly charged without having to tap into it for gauges.
Ambient temperature only affects running amp draw and has nothing to do with startup.

The high altitude issue is with the generators. They lose power as density altitude increases (elevation and temperature increases). I might look into changing the jets, which will help. I live at 5400' and rarely go below 4,000' elevation.

mfifield01 · 05-16-2016, 12:05 PM

I just read through this and some other websites. Do they Dometic Brisk Air II A/Cs (15k in my case) already have a sufficient Hard Start Capacitor from the factory? Does adding the SPP6 help with generator starting?

My generator will start my A/C, but Eco Mode needs to be turned Off. It would be nice to leave Eco On.

jsmith948 · 05-17-2016, 04:34 AM

Quote:

Originally Posted by Desert185

The high altitude issue is with the generators. They lose power as density altitude increases (elevation and temperature increases). I might look into changing the jets, which will help. I live at 5400' and rarely go below 4,000' elevation.

This is interesting - so, if I take a 3100 watt generator up to my DB's place in NE Nevada (6900') there is a chance it will no longer provide enough power to run our 13,500 a/c?

Desert185 · 05-17-2016, 09:17 AM

Quote:

Originally Posted by jsmith948

This is interesting - so, if I take a 3100 watt generator up to my DB's place in NE Nevada (6900') there is a chance it will no longer provide enough power to run our 13,500 a/c?

Here's some background info on the subject:

http://www.rvtechlibrary.com/generator/altitude.php

Some recent personal experience:

I have two Smarter Tools 2000iQ gens with the Yamaha MX80 engine. I didn't have the requirement to run them much last year, so the break in oil change was done just before my trip a few weeks ago when I used Mobil 1 10W-30.

The dry camping spot was at 7300' with a day time temperature raising the density altitude to ~9000'. The power loss can be significant without a carburetor jetting change, and even then, the power loss can't be compensated for to recover power to sea level rated power. My carburetor equipped 2002 quad runs rough at 10,000' without taking into account temperature. Fuel injection is the way to go these days and my fuel injected RZR, even without an O2 sensor, runs really well.

I was wondering how my gens would do. I never really ran the AC because of the temperature, but I did run the fireplace, the microwave and the Keurig one at a time with only one gen. The Keurig, rated at 1450 watts, is the biggest demand and the gen is 1600/2000 watts. So at 9000' density altitude a single gen had no problem powering the coffee maker even though you could tell it was making an effort.

Generator rejetting is usually categorized into three altitude requirements, sea level to 5,000', 5000 to 10,000' and above 10,000' in three jet size steps. Given the performance of my gens at a density altitude of 9,000' with synthetic oil, good gas and clean air filters, I am not going to go through the process of changing jets for the 5,000-10,000' normal operating environment. Gas consumption was within spec and some choke was needed for the start, although not for long after the start. I suspect these are Kalifornia spec jetted to run a bit lean for CARB requirements. Given all this, I don't think you should have any concerns.

As a side note, I change the gens oil after each camping use. It takes less than a quart, and I even have enough left for the Honda 1000, if it needs a change. They're then ready for the next trip that might require 4-6 hrs a day use for 5-14 days. They are really running well, either due to being fully broken in or the Mobil 1 synthetic or both.

PS...I saw a comment about loss of power percentage due to altitude and the commenter also said that would also equate to loss of wattage output. If that were the case, my 1600/2000 gens would not have run the 1450 Keurig. Bogus statement...

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