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 > Underperforming front A/C?

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novasbc

Waco, TX

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Posted: 07/09/18 07:03pm Link  |  Quote  |  Print  |  Notify Moderator

Background, I have a 2018 palomino puma unleashed toy hauler fifth wheel, with dual A/C (351THSS).

I took it in almost immediately complaining that the front a/c hardly did anything. They said they fixed it, and it was better, that there was foil blocking the vents. I felt like it still didn't do a good job, but it was getting into colder months and I really couldn't tell.

This year as it got hot, it was apparently still sub par. The lesser power unit in the garage does a much better job than the one in the front, so much so that the only way to cool it down is to put a fan in the back and blow it up to the front.

I brought it in again before the 1 year warranty was up, and they say it's performing to specifications. I have measured the air temperature coming out of the vent and yes the temperature is good, but it just seems like such low volume it can't keep up.

The other night I didn't run a fan from the back to the front, and it couldn't even get it below 80 degrees (this is Central Texas, I would think this is possible at night.

So my question, how can I either validate that it's performing to spec, or prove it needs work?

If I didn't have the garage ac I can't imagine how terrible it would be. Yes, in Texas having two seems necessary, but seems wrong never the less.

The air that comes out of the vent in the front master bedroom is barely a trickle, while in the back it's blowing like a storm.

When I checked the temperature at the vent, it was putting out 55 degree temperature, so more than 20 degrees below the outdoor temperature.

Thanks!

Mark.

dougrainer

Carrolton, Texas

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Posted: 07/09/18 07:19pm Link  |  Quote  |  Print  |  Notify Moderator

The ONLY way to verify the AC unit is running to spec, is a Temp corrected AMP draw of the compressor. That is what I would do if you were my customer. You look at the SPEC plate of the AC. On that spec plate will be the AMP draw of the compressor. That amp draw is based on 95 degree ambient temp. You run the AC for a minimum of 15 minutes and then take the amp draw with a digital clamp on meter of the compressor wire. For EACH 10 degrees above 95 ambient you add 1 amp to the draw. For EACH 10 degrees below 95 ambient you subtract 1 amp. So if your AC spec is 12.8 amps for the compressor and it is 85 degrees ambient the compressor amp draw should be about 11.8 amps. This just verifies the unit is running to spec. It does NOT give you clues if the AC system is not installed to spec with the baffles and ductwork sealed correctly. If the unit is running to spec, then you dig deeper to find if there is a problem with distribution of the cold air. You also need to verify the SIZE of each AC unit. They will be either 13.5k BTU, 15k BTU or HC. HC is a model that is slightly lower than 15k BTU but is almost 15k BTU. If you post the Model number and brand of each AC I can give you the BTU size. Doug

mlj427

Mechanicsville Maryland

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Posted: 07/10/18 12:08am Link  |  Quote  |  Print  |  Notify Moderator

Pull the vents out and use your phone to photo the duct work and see if there is still a blockage.

prichardson

Lafayette, La

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Posted: 07/10/18 07:38am Link  |  Quote  |  Print  |  Notify Moderator

Check for restriction in the ductwork and also drop the plenum cover and make sure that it is properly sealed to the duct system and not leaking into the attic.

the bear II

Torrance CA.

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Posted: 07/10/18 08:20am Link  |  Quote  |  Print  |  Notify Moderator

I would check the air speed coming out of the vents for the rear AC and compare with the speed from the front AC unit. That will tell you if the fans are putting out similar volume of air.

As long as the temp coming out of the vent is at least 20 degrees below the outside temp it sounds like it's in specs for cold air output.

wa8yxm

Wherever I happen to park

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Posted: 07/10/18 09:15am Link  |  Quote  |  Print  |  Notify Moderator

When it comes to air flow I see some very "Strange" results on my Dual Ducted System. OFten I will get more air flow from selected vents or so it seems. with one or the other running. and less with both running. Or so it seems.

Another thing.. Both my 15K jobs work well per testing but the front one is "less effective" Cause the FRONT is bigger. WAY bigger.


Home is where I park it.
Kenwood TS-2000 housed in a 2005 Damon Intruder 377


Chris Bryant

Arden, North Carolina

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Posted: 07/10/18 09:53am Link  |  Quote  |  Print  |  Notify Moderator

Another vote for checking ductwork. OEMs are notoriously bad at sealing it.


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ScottG

Bothell Wa.

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Posted: 07/10/18 10:15am Link  |  Quote  |  Print  |  Notify Moderator

Check to make sure there are ends on your duct work and that they are sealed. Also make sure they aren't collapsed.


Scott, Grace and Wesly
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smthbros

WI

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Posted: 07/10/18 12:29pm Link  |  Quote  |  Print  |  Notify Moderator

Chris Bryant wrote:

Another vote for checking ductwork. OEMs are notoriously bad at sealing it.


I wonder how competent they are at duct design? Many have reported on the 20° temperature drop for air through the evaporator. Keep in mind the temperature drop is dependent on the volume of air through the evaporator.
Do you have specifications on air flow for RV air conditioning units?

Chris Bryant

Arden, North Carolina

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Posted: 07/10/18 02:04pm Link  |  Quote  |  Print  |  Notify Moderator

smthbros wrote:

Chris Bryant wrote:

Another vote for checking ductwork. OEMs are notoriously bad at sealing it.


I wonder how competent they are at duct design? Many have reported on the 20° temperature drop for air through the evaporator. Keep in mind the temperature drop is dependent on the volume of air through the evaporator.
Do you have specifications on air flow for RV air conditioning units?



There are fairly strict specs for duct design. You can find some of them here, an older Briskaire install manual. The problems now are more in implementation, rather than design. They gave the right sized ductwork, the right vents, etc, but for seal anything, and often don't terminate the ducts. A bit of work can pay big dividends.

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