Fresh Air Vent - Central AC, Inefficient Cooling


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Old 08-28-13, 07:31 AM
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Fresh Air Vent - Central AC, Inefficient Cooling

Hello All,

I have a question about a fresh air vent that is installed on the air handler on my central AC System.

This fresh air vent was installed by the previous owner, the air handler did not come with this option. Essentially a hole was cut on the opposing side of the air handler where the intake ducting is mounted. A make shift filter was installed where the fresh air vent ducting meets the air handler. There is a valve open or close the fresh air vent. Because it is now summer on the West Coast, I have the fresh air vent closed, and to be honest it was left closed through winter because we only use the heater a hand full of times during the Winter.

*Air handler mounted in the attic, on its side on the second level of a 1100 Sqft Home.

We've always struggled with cooling our home and I have taken the steps to be sure the system is running as efficient as possible. IE: Changing Filters Often, System Recharge, and General Routine Maintenance (Cleaning the Compressor, Vents). The home is only 15 years old, and the insulation seems good.

Would it be a good idea to just seal this vent off completely? Disconnect it from the air handler and seal the hole that was cut. Something tells me I am still pulling some hot air from fresh air vent even though it is closed, simply because it is some what of a hack job.

Something else I thought of was the sun beats on the side of the house where the Condenser/Compressor is located, the coolant lines are plumbed inside the a wall that gets the most sun, as it makes it way to the attic. The insulation on these lines in the attic is looking a bit tired, however it is still intact. Is it time for new insulation on the coolant line feeding the air handler? Possibly loosing some of its cooling power as it is pumped up to the attic?

Another note, our attic only has 2 Gable Vents, and it gets very very hot up there. From what I've been told, the heat in the attic wont effect the performance of the air handler? Which completely defies my logic of the Central AC System.

Any feedback would be appreciated.
 
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Old 08-28-13, 07:56 AM
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1) Patch up that fresh air vent, you only want inside air circulating through your air handler.
2) Get some shade on the condenser, it will work more efficiently and last longer.
3) Although the air handler and duct work is insulated, the cooler you can make your attic, the less load on the components. A thermostatically controlled power vent will help.

Refrigerant is pumped into the air handler on the high (hot) side (smaller line with no insulation).
The insulation on the suction (cold) side is there to stop it from sweating and to stop any excess heat from being absorbed into the system as the refrigerant makes it's way back to the compressor to start the condensing (heat removal) cycle over again.
 
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Old 08-28-13, 08:04 AM
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If that was me I'd close that makeshift fresh air vent off permanently.
I've seen them put on furnaces in a basement as a way to pressurize a house against radon.
Not terribly effective in that role either.

From what I've been told, the heat in the attic wont effect the performance of the air handler?
It's not supposed to but it does. Insulation is not 100%perfect and heat does get into the air handler and the duct system.

Not only that....the excessive heat in your attic also permeates to the floor below it. Proper airflow within the attic is very important.
 
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Old 08-28-13, 08:14 AM
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Thanks!

I am going to seal of the fresh air vent tonight.

Then look into the attic fan.

I will report back tomorrow.
 
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Old 08-30-13, 11:37 AM
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Hey guys, got the fresh air vent sealed off.

While I was up there losing all of the water in my body by means of sweat, I found a few leaks were I could feel cool air blowing out of the air handler and sealed them with foil tape.

After all that, I took a supply reading, and return reading.

Supply: 61 Degrees F
Return: 71 Degrees F

My readings were acheived by using a remote outdoor thermometer stuck to the center of each vent for about 30 minutes.

Thermostat which is about 6 feet from the return was reading 80 Degrees. It took 3 Hours to drop 2 Degrees in a 1100 sqft home with an outside temp of 90-88F.

I am no expert, and can't say my readings are accurate but if it is only a 10 degree split, could I have a problem?

Also, the return suction increased after sealing the vent. I cant hold the filter 2-3 Inches away and it will suck it up into place. The return looks like its about 16in".
 
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Old 08-30-13, 01:56 PM
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After all that, I took a supply reading, and return reading.

Supply: 61 Degrees F
Return: 71 Degrees F

My readings were achieved by using a remote outdoor thermometer stuck to the center of each vent for about 30 minutes.

Thermostat which is about 6 feet from the return was reading 80 Degrees. It took 3 Hours to drop 2 Degrees in a 1100 sq.ft. home with an outside temp of 90-88F.

I am no expert, and can't say my readings are accurate but if it is only a 10 degree split, could I have a problem?

Also, the return suction increased after sealing the vent. I cant hold the filter 2-3 Inches away and it will suck it up into place. The return looks like its about 16in".
A 10°F drop is not adequate, at 50% relative humidity in your home the indoor temperature drop should be around 18°F.

When you have checked the humidity level in your home outside and check the discharge temperature coming off the condenser, then compare that to the outdoor temperature, at 50% relative humidity in your home and normal airflow, at only a 71°F indoor temperature, the temperature rise off the condenser on a 10 or 12 seer unit would probably be around 17°F or less.

If the outdoor discharge air from the condenser is way above 17°F, then you probably have hot attic air leaking into the return air system.

Attic air areas are usually very hot and carry a lot of grains of moisture, even though it may not have a real high humidity level.

What tonnage is your condensing unit, considering the way the filter is sucked into the rack you may have a way oversized air-conditioning unit.

That can lead to numerous problems including short runtimes and insufficient humidity control, which should be at 50% or less humidity.

Try to read the model number of the condensing unit and try to find out what the tonnage is on it, if you post the model number here we can probably tell you what the tonnage is. With only 1100 ft.² of conditioned area that should not need a very large condensing unit.

There may be literature somewhere in your home and a owner's manual, see if you can located it.
 
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Old 08-30-13, 03:32 PM
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I've seen lazy contractors add a vent to an outside package unit to make up return air for undersized return, never seen one in an attic situation. (BTW killed the heat exchanger outide) As was said, oversized system or undersized return ducting. Odd thing is that I would think you would have a higher split than lower if the airflow was bad and it would be freezing up. Another possibility is it's over charged trying to compensate for poor air flow. You need a second opinion from someone that knows ducting and refrig.
Edit.....if you do call someone, make sure they know what a magnahelic gauge is and how to use it.
 
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Old 09-04-13, 06:32 AM
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Thank you for the valuable insight.

I am going to take some temps off the condenser and in the attic today and get the size of the unit.

I will report back with a more detailed post.

Also wanted to note that when I pulled the filter off the return the air flow increased at all the supply vents, so much so you could hear the air rushing out. It actually cooled the house down 2 degree's in 30 minutes.

I've been using a 3M Allergen Filter, I went and got the basic filter to allow more air flow. That seemed to help, however, like others have said, I suspect that the return is also undersized, and that "fresh air" vent was installed to compensate.
 
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Old 09-04-13, 06:35 AM
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Lazy and cheap. Tract housing, our roll up garage door only had 1 torsion spring when there should have been 2!
 
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Old 09-04-13, 11:54 AM
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While I agree that "lazy and cheap" is often the excuse behind inadequate ductwork in residences it is not always the reason. There are a number of architects that have no training in HVAC and as such they leave no room in their designs for adequate ductwork or for optimal furnace placement. The builder, who also has no training in HVAC design or installation is then left to fit what he/she can into spaces that are simply inadequate for the job. The result is poor performance.
 
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Old 09-05-13, 10:10 AM
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The rise off the condenser was 100F, outside temp was 92F.

I wasn't able to get the humidity, and forgot to get the seer rating! Ugh.

I had another thought, is it possible to reset the air handler, t-stat and condenser, besides just unplugging, or throwing the breaker? Would that help in some way at all?
 
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Old 09-05-13, 10:52 AM
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3M is the worst for an undersized duct system. If you saw improvement but still not satisfactory results, I'd have someone look at the design on a cool morning and make a recommendation on how to improve it. Might not cost as much as you think. 8 deg. split outside tells me you have a refrig. problem. (duh) IMO it's time to call someone that won't just make it cold in the house, but find a solution to what you have described here. An A/C shouldn't be charged until airflow has been determined adequate.
 
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Old 09-06-13, 07:34 AM
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The system was 3lbs low on Refrigerant, and was recharged in the spring on last year. Possibly over charged?

I took a temp reading in the attic at 5:30 PM yesterday, 101F in the attic and 91F outside.

The condenser is a 10 Seer.

This is very similar to how the air handler and evap coil is mounted in the attic. When we moved in, it looked like the filter had not been changed in a while, and it was the incorrect size, so the only part of the filter that was dirty was circle center when it was sucked up against the return. Possible the coils are dirty?

Name:  air-handler-evaporator-compartment1.jpg
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Old 09-06-13, 07:43 AM
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Spec Sheet based on the condenser model number FBA018GC1

http://icpindexing.toddsit.com/docum...2141120106.pdf
 
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Old 09-06-13, 07:51 AM
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3 pounds low last year, the fix was a recharge and now your not cooling again?
Pretty simple to point to a leak in the refrigeration circuit. Your low again.
Don't let a tech come out and simply put refrigerant in it, they need to troubleshoot and find the source of the leak.
 
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Old 09-06-13, 08:16 AM
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The same tech that charged it in the spring last year, came out this spring because I was trying to avoid this from happening again and he said the system was still charged, and said it was a even a bit overcharged.

He also said it may have something to do with the TXV and the "Filter" indicator on the Honeywell Thermostat. I not really sure how that will effect the cooling. Maybe someone could shed some light on that?


When I got home at 5PM yesterday it was 92F outside, set the AC at 78F when I left in the AM, when I returned it was at 80 Degrees and didn't drop to 78F till 8PM. Ran consistently for 3 Hours. I bought a $120, 5,000 BTU Mini Window AC for just our bedroom at night because it's a waste to run the Central AC. That little thing works so well, has the temp down to 72 in under an hour! Even with the humidity from the shower.

Thanks again for all the help, and everyone input. Unfortunately I am one of those people that obsesses over things till I am educated and confident I understand the problem, and the correct solution.
 
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Old 09-06-13, 09:35 AM
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Unless I'm missing it, I'd be obsessing over not having a secondary drain pan. If that ever leaks (and it will someday) you will have ceiling damage below.
 
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Old 09-06-13, 12:22 PM
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The above picture isn't the OP's system.

If the same tech that put refrigerant in it last year is telling you that this year it may be over charged, you need to find a new HVAC company. PERIOD!!!

1) Three pounds low is excessive loss.
2) If it was charged correctly last year (systems don't make their own refrigerant) then there's no way it should be over charged this year. Doesn't make any sense at all.
3) Your temp splits, both on the condenser and evaporator are pointing to a low charge. (refer to #1 for the reason)

The $120 spent on the window unit should have gone to a reputable HVAC company to fix the system.
 
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Old 09-06-13, 01:20 PM
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My bad...after re-reading I see it's similar. When he said he was in attic to measure temp I "assumed" it was his system. I agree money would have been better spent on fixing the problem instead of a bandaid, but I also know that if mama isn't happy, no one is happy.
 
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Old 09-09-13, 10:23 AM
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*Raises White Flag*

I've surrendered. I have a different AC Tech coming out on Wednesday. Hopefully we can get this thing solved.

During our "heat wave" I asked a few of my neighbors who have very similar homes and the same systems if they were about to achieve 78 degrees during these hot days, and they all said it would. So it's obvious it have a problem.

I am hoping the last guy that came out didn't just put air instead of refrig. into the system as a "recharge" just to hit the systems pressure specs!
 
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Old 09-09-13, 10:27 AM
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I just read my spec sheet that says it was factory charged with R22, I am almost positive the last AC tech put R-410A into my system.

Ok to mix?
 
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Old 09-09-13, 10:34 AM
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Not ok to mix. If you have proof of the mistake, I'd be calling the service manager or owner of the company that added the wrong refrig. asap. Static pressure reading by a pro will be able to tell.
 
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Old 09-10-13, 11:32 AM
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Wanted to note that I found a hole the size of a golf ball behind the thermostat....

Seal it up, and the temp dropped 2 Degrees....
 
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Old 09-10-13, 12:49 PM
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So T-Stat not reading the indoor temp correctly had you fooled or is it really still warm in the house?
Did we ever get the temp split readings?
 
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Old 09-10-13, 01:16 PM
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Let us know what the tech has to say that comes out on Wed. I think it's more than just a hole behind the stat.
 
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Old 09-12-13, 07:14 AM
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Tech came out yesterday.

There's a refrigerant leak. Its low on refrigerant. However, he did not say how low.

We are getting a 15 Degree split. 75 Return, 60 Supply.

He said the job of evacuating the system, then using a sealant in the lines, followed by a full recharge would run about $1200.

Might as well just upgrade to a newer, larger, more efficient system.

He checked the air handler's blower and coil. Everything was clean.
 
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Old 09-12-13, 10:36 AM
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Others will probably chime in, however using a sealant in an A/C system is NOT recommended and is a last resort. While it may plug the leak, it may also plug some of the tiny openings in the coils (evaporator & condenser). Many A/C techs will refuse to connect their pressure gauges to a system that has sealant in it, since it can ruin their gauges. I would think twice about purchasing a new system from this tech or his company.
 

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Old 09-12-13, 12:24 PM
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You have a system that needed more return air before. Find someone to evaluate your duct work and recommend what to do from there. Bigger is not going to solve your problem, only make it worse.
 
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Old 09-12-13, 02:00 PM
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Do not allow any company to put a sealer into the system. It should be inspected with the proper equipment to find the leak. Sometimes a simple repair at a fitting is all that's needed. All the brazed joints can be easily inspected. If the leak winds up being in either the evaporator or condenser coil, that's when you should look at a system replacement. You should be an educated consumer and call the tech back or have the company send another tech to look for the leak. I would be very hesitant in purchasing a new system, I think you're being up sold.
 
 

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