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Old 10-18-2020, 04:12 AM   #1
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Reduced air flow as A/C units age.

Air conditioner air flow from our front Penguin II seemed normal but the AC unit was 12 yrs old or so and has run full time living in Central Fl for the past 7 years.

Noticing any slowly reduced air flow is not likely but after replacing the 15K unit with a 13.5K and having the air flow seem to almost double stunned me.

The old AC's have been well maintained. Cleaned at least every 6 months until water is clear pouring through all of the condensers.

However my suspicion is that some accumulation of build up on the condenser coil may not be removable.

More information on why the change of AC. It was old and worked way too hard and had begun tripping the breaker far too often. I don't want to stray off into weak breakers etc. Just suffice it to say I am a certified electronic tech and the thing was just beginning to draw far too much current.

Caps, et all have been replaced over the years. It did not have a hard time starting etc.

What I am curious about is the air flow and what someone that deals with AC's might have found over the years.

The single motor of the unit was showing signs of a bearing losing grease on one end so the motor could have been dragging a bit but certainly not enough without putting out some gruesome noises and it was not.

With the new 13.5K unit in place the air flow has almost doubled. I have a rear 15K unit still in place and have that to compare with. That one too needs replacement. It cycles on and off far to quickly. And it is not getting as cold as it used to.

Perhaps the thinner design of the 13.5K coils allows more air flow or as I suspect, the old coils were just worn out and not letting the air through.

Inquiring minds want to know.

And since I have an old AC unit on the ground I have been busy designing some condensation drains. It's more difficult that it looks but this group most likely has some great designs. I have a decent design but do not know where to have them molded. Any suggestions would be appreciated.

Keep cool my friends.
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Old 10-18-2020, 07:25 AM   #2
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The fan motor bearings drag slowing the speed which reduces airflow which causes higher compressor pressures which results in higher amp draw which trips the breaker. Sounds normal to me. Replace the fan motor and see what happens.

Also the installer may have done a better job of sealing the output air at the duct which may be where your airflow is going
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Old 10-18-2020, 08:49 AM   #3
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The fan motor bearings drag slowing the speed which reduces airflow which causes higher compressor pressures which results in higher amp draw which trips the breaker. Sounds normal to me. Replace the fan motor and see what happens.

Also the installer may have done a better job of sealing the output air at the duct which may be where your airflow is going
Thanks for the feedback. The air ducts and air flow was long ago addressed by me and I am type A for sure. I improved the air flow immensely at that time.

I decided to not toss money at a 12 yr old unit that has run almost 24/7 for years. The hard part was getting a new one. None have been available until lately. I had to settle for the 13.5 because the 15K unit was not available. I am incredibly pleased except for the poor quality control during the build of the AC.

I had to change the circuit board right out of the box to make it compatible with the old thermostat so I have a shiny new ckt board laying about.

When I tested the fan by hand (poor test I know), it was as easy to turn as the new one but the grease spot below the outside bearing was very telling.

A thought just came to me in comparing the evaporator or condenser whatever it is called, to a vehicle radiator. They have all kinds of issues and I can remember having to clean bugs out often living in a rice belt area where mosquitos were the state bird. I tried my best to clean the ac's often but perhaps some sort of electroylsis builds up or just some sort of crud eventually reduces the air flow.

Again, thanks for the input.
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Old 10-18-2020, 08:58 AM   #4
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I would say that a 12-year old air conditioner that has been used full time is ready for replacement. It is not surprising that it is tired after that much use.

I only wish the A/C's in my stick home in Florida had lasted that long. (Big house with 4 A/C's). In many cases, they were shot after 6 or 7 years, or even sooner.
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Old 10-18-2020, 09:37 AM   #5
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I would say that a 12-year old air conditioner that has been used full time is ready for replacement. It is not surprising that it is tired after that much use.

I only wish the A/C's in my stick home in Florida had lasted that long. (Big house with 4 A/C's). In many cases, they were shot after 6 or 7 years, or even sooner.
I hear that a lot and like to compare my situation, I normally do all of my A/C repair and troubleshooting. My Arizona stick house has the original two 1993 R22 units which are working fine. I replaced the compressor in one of them twice and several condenser fans, capacitors, a control board etc.. When the last compressor failed I asked a friend in the A/C business his opinion and he said his check book balancing shows a $800 compressor is a better deal than a $4000 unit. That was several years ago. He also said he likes folks that want to replace old units as there is good money in that.

My camper has three 15,000 units. Two are original 2007 R22 units and a previous owner replaced the rear unit with a R410 unit. Service documentation showed a history of excessive heat in the rear. I found the air was blowing out the end of the ducting as the factory never put an end cap on it. One of these days I may replace the fan motors as they naturally slow down as the bearings get dirty from usage.

I received a call this week, stick house rooftop unit (vintage around 2000) no cold air. The evaporator was covered with dirt (not changing filters). I cleaned it & the unit worked fine for a bit but the condenser fan amps were high and the compressor shut down. The fan spun freely. I replaced the fan motor and it has been working fine with the 100+ temperatures ever since.

I understand the labor charge balancing act between repair vs replace depends on the repair man. Is he a technician or a salesman?
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Old 10-18-2020, 04:40 PM   #6
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FWIW, air volume through the condenser coil (hot refrigerant) does not effect air flow through the evaporator coil. The are two different units/radiators. The condenser coil is outside on the roof, the evaporator coil is at roof level and the air flow is inside the RV.
Have you checked to make sure there is no cross-flow at the plenum between chilled air and intake air?
There are two things to cause reduced air flow through the coils, fan and/or motor defective, and clogged fins.
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Old 10-18-2020, 05:15 PM   #7
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Yes I am aware they are two different radiators as such. They are completely isolated from each other via plastic housing and foam insulation to make sure the air flows through the outside radiator part.

The roof AC on our units has one fan motor and two squirrel cages. One runs the inside air flow of course and the other cools the radiator.

As for the home AC unit. I was stunned after tossing lots of money at that one. It had gone through a motor and a couple of refills of refrigerant. A new one was 4K + but I'm a do it yourselfer and had a new one in place for less than 2K, including a heating element. Sure discouraged to see how bad the thing looked inside after just four years. The moisture here in Central Florida sure takes a toll on things. My AC in California lasted over 20 years.
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Old 10-18-2020, 05:36 PM   #8
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FWIW, air volume through the condenser coil (hot refrigerant) does not effect air flow through the evaporator coil. The are two different units/radiators. The condenser coil is outside on the roof, the evaporator coil is at roof level and the air flow is inside the RV.
As YC1 mentions above, there is just one fan motor which blows air through both coils. When it starts dragging it affects the condenser, compressor, evaporator and ultimately the humanoid.

There are RV A/C units that do have separate fans.
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Old 10-18-2020, 09:42 PM   #9
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As YC1 mentions above, there is just one fan motor which blows air through both coils. When it starts dragging it affects the condenser, compressor, evaporator and ultimately the humanoid.

There are RV A/C units that do have separate fans.
Thanks for refreshing my memory, it's been 8 years since I had a roof A/C unit.
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Old 10-19-2020, 06:47 AM   #10
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I love this forum.

Take what appears to be a simple problem can actually be an accumulation of multiple issues. There is never just one thing broken in an RV.
There is a minimum of two and likely three. It is part of the manual bylaws.

There shall (shall meaning must or mandatory), that while in or around any RV weather new or previously owned, that there be a minimum of two issues. These in part may be related or not however it is suggested that the owner must be driven close to the brink before resorting to the helpful friends at IRV2.com

When helping one of my grandsons changing his roof AC I found it had two motors which seemed to be a good design. I suspect it is easier to balance it. However it was not well made. Quite flimsy and floppy all over. It took three of them to get one that was not busted up during transit and it turned out the last one had a broken squirrel cage on one fan.

The two fan idea seems ideal to get optimum cooling and in addition they ran the condenser coil drains along the bottom and below the rear fan. That fan picks up most of the condensate and shoots it over the outside set of coils. Seems like a good idea or a recipe for corrosion/ electrolysis.

I should have carefully taken the old one apart but did not want to release the gasses accidently. The fins were not smashed or did not prevent a decent spray of water being passed through.

I believe the new unit with the slimmer condensers allow much more air flow. Looks like they used the same motor as the old one. They added some form fitted styrofoam over the plastic shroud that houses the inside condenser. That looks like a good idea as well. There is a lot of heat in that area and this probably makes it a bit more efficient. I also noticed the outside shroud has additional breather holes along both outside edges versus just the one on the old ac. This appears to reduce the air restriction for the outside condenser.

The compressor looks like the same one. All in all, if they had paid attention on the assembly line it would have been a 5 star product. Not many choices when replacing one unit but I would tell anyone changing one to open it and inspect it closely for pinched or loose wires.
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