Home A/C question

You'd be surprised how fast those things get clogged, especially if it is a "high filtration" type low-micron rated to allergens etc. As a new homeowner not used to it yet, you should check it every month (just make it like the first or last day for ease), after awhile you'll figure out about how regularly they need to be change out.

My money is on the restricted airflow slowly killing the motor, it built up enough resistance to pop the capacitor.
 
RatLabGuy said:
You'd be surprised how fast those things get clogged, especially if it is a "high filtration" type low-micron rated to allergens etc.
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If it whistles or bows in or anything like that when the unit is running, then the static pressure across the filter is way too high. The one thing you need to keep in mind is that there may not have been any proper engineering done on that system, or what was done was 20 years ago, before MERV 8 and 11 filters were common. It could be that the filter area is too small to accommodate a filter like that. I know I had to almost double the filter area in order to get ours to a happy place with a MERV 8 filter.
 
ok while I hopefully still have you guys attention....

My house AC cannot get the house below 77-78 during the heat of the day. We have spent money insulating and installing black out curtains to try and keep the temps down. The fan in the outside unit was replaced last year because it fried and the system was recharged and the same time. We have bought a new house and this one is for sale currently but until we move in october I dont think I'll survive coming home to a hot house from working 10+ hours in a hot shop everyday.

I was once told that the air coming from the vents should be around 15 degrees cooler than room temperature and it's at best 10 in the coolest part of the night. usually more like 5-8 best I can tell. Sooo I went up in the attic yesterday looking for anything that could be causing problems. First I found that where the high and low pressure copper lines go into the unit it's not sealed and a ton of cool air is being blown into the attic instead of through the vents into the house. I plan to fix that even though I expect little results. Second the low pressure line seemed cool to the touch and the high pressure was fairly hot as it should be I suppose. How cool and hot I do not know but something that seemed odd is that I can hear and feel the high pressure line burping. Is that normal? It's like someone is pumping wet sand through a tube at high pressure. I would expect the high pressure Freon to dead head at the expansion valve and just bleed off slowly but it doesn't seem like it is to me. Could this just be low Freon? We've always had trouble keeping our upstairs cool in the summer. I can deal with that because we're only up there to sleep and its bearable in the evening and morning but the rest of the house has got to get better. Please HELP!
 
It sounds low on freon so you should get that checked out BUT that air leak into the attic will make a bigger difference than you think. I'd get that fixed up too.
 
Easy stuff first - how is the pressure/air flow at the vents? Is the filter clean? House has always been this way?
FYI You might be surprised what a difference it can make to have those lines sealed. One winter I bought an airflow meter, then spent several evenings mudding & taping all teh joinst in our system, them measured again... was surprised to see it went up > 20%

but as above it does sound like a freon leak
 
Yea filters are cleaned or changed regularly. We've been here six years. Id say it hasn't been bad till the last 2 or so.

Air flow at the vents isn't terrible. They're in the ceiling, you can feel air moving sitting under them on the couch. Are you suggesting that the duct work could have an obstruction? I hadn't thought about that.
 
I hear about people getting their ductwork cleaned and it making a big difference but I can't imagine that enough dust or anything would actually build up to block a 6" hose?
 
I'm a shadetree AC person so really don't know squat but a couple thoughts come to mind. Any chance the ductwork has a hole somewhere in the return thus sucking in hot humid air outside the insulated home capsule? I don't know what you have but I have been told the flexible duct tubing is notorious for disintigrating over time (not that much time either), especially the black plastic covered flex ductwork. Maybe irrelevent to this discussion but I was thinking if you are sucking in 'outside' air you are continually dehumidifying that rather than starting with the indoor air. I think an 18-20 degree differential isn't out of the ordinary to expect. I keep my T-stat at 79 and I am pulling 78-79 degree air at the return and putting out 59-60 at my register closest to my air handler (about 5 ft run is the closest). I get 65-68 degree at the furthest which has to be a good 25 feet across my attic which is hotter than hell in the summer. I just have the black crappy flex insulated ductwork. It does sound though like a freon level problem. Too much or too little are both bad situations (too much probably worse!) since you don't get the evaporation where/when you need it to get the heat exchange in the coil itself. Also, have you checked both the evaporator coil for being clean as well as the condensor (outside coil) so you have good air to coil heat exchanging going both ways?
 
MarsFab said:
I hear about people getting their ductwork cleaned and it making a big difference but I can't imagine that enough dust or anything would actually build up to block a 6" hose?
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No. The only significant impact you're likely to see there is a reduction in allergens, etc. And if the ducts have been kept halfway clean (especially so if they're overhead and crap can't fall into the vents), you're unlikely to see much of a difference there.

Focus on making sure that the return duct is only pulling in conditioned interior air, and that the supply ducts aren't venting into unconditioned space.

The freon suggestion is a decent one, too.
 
This house we have now never seemed to cool this house down when we first bought it. Had a year old unit on it that was the right size everyone said even the manufacturer. Had 4 different shops come out and said freon was correct and tried using diverted and other crap. Finally a 5th company came out as and the first thing he said was it is low on freon . It has this newer stuff and the settings were higher. Come to find out it still just had the stuff from the factory or something like that and had not been filled to the proper specs. We had had the same issue with it not cooling worth a shit. Could not keep up in August when we had moved in. Now we just use the only company that had a clue.
 
benmack1 said:
I'm a shadetree AC person so really don't know squat but a couple thoughts come to mind. Any chance the ductwork has a hole somewhere in the return thus sucking in hot humid air outside the insulated home capsule? I don't know what you have but I have been told the flexible duct tubing is notorious for disintigrating over time (not that much time either), especially the black plastic covered flex ductwork. Maybe irrelevent to this discussion but I was thinking if you are sucking in 'outside' air you are continually dehumidifying that rather than starting with the indoor air. I think an 18-20 degree differential isn't out of the ordinary to expect. I keep my T-stat at 79 and I am pulling 78-79 degree air at the return and putting out 59-60 at my register closest to my air handler (about 5 ft run is the closest). I get 65-68 degree at the furthest which has to be a good 25 feet across my attic which is hotter than hell in the summer. I just have the black crappy flex insulated ductwork. It does sound though like a freon level problem. Too much or too little are both bad situations (too much probably worse!) since you don't get the evaporation where/when you need it to get the heat exchange in the coil itself. Also, have you checked both the evaporator coil for being clean as well as the condensor (outside coil) so you have good air to coil heat exchanging going both ways?
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The Intakes sucking in warm humid air is a good thought. I'll definitely have to check them out. In my case the upstairs is always 10 degrees warmer than downstairs. We don't have dual zones but there are 2 intakes. One up and one down. So the upstairs intake is always drawing in the hotter air. It also happens to be at the top of the stairs. Do you think it would make any difference to put a fan at the bottom of the stairs blowing the cool air up towards it?
 
Might experiment by putting some restriction on the downstairs return vent. That will increase the pressure on the lower level, encouraging more air to exit from the upstairs supply vents and (due to the restriction in the return line), increase the amount of return air that's coming from upstairs.
 
Not good but that's where it gets weird. I have two intakes. One up one down. But only one outlet. That one outlet runs into a big rectangle distribution box that has all the smaller lines coming off going to each room.
The back two rooms upstairs always stay the hottest and they are the first two pipes to break off of the distribution box. The coolest rooms are the furthest from the inlet in the dist. box. It's like all the cool air blows right past every outlet and goes right out the two in the end. I guess it should be baffled but doesn't seem to be.

So why two intakes if only one outlet?
 
shawn said:
Might experiment by putting some restriction on the downstairs return vent. That will increase the pressure on the lower level, encouraging more air to exit from the upstairs supply vents and (due to the restriction in the return line), increase the amount of return air that's coming from upstairs.
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I've tried that. I expected it to work but probably make the system work a bit harder. It only seemed to make the downstairs hotter and the upstairs stayed the same and it got progressively worse because the cool air it normally drew I'm from downstairs was only warmer. I think the key is to get the cool air coming out even cooler. I'm afraid that's gonna cost me :(
 
RatLabGuy said:
How is the pressure on upstairs vents compared to downstairs?
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Like I said in post #39 the pressure up is much lower than down. How can that be if the cool supply is all coming from the same dist. box. And there are no adjustable baffles or anything on the box.
 
MarsFab said:
Like I said in post #39 the pressure up is much lower than down. How can that be if the cool supply is all coming from the same dist. box. And there are no adjustable baffles or anything on the box.
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I'm having a really hard time visualizing the topology of your system, it sounds really complex. Is the main fan & unit down in the basement or in teh attic?
They may not have sized the ducting properly, it should taper down in size with distance & amount of take-off so that the pressure stays constant.
This is aparently a common error, in my house (a long 1-floor rancher) the room at the far end has crappy pressure b/c its at the end of the line.
 
Chris,
I'd bet dollars to donuts your supply trunk line is sized improperly...but then again most are.

On the returns are you sure the 2 dont T together at some point?
 
I don't think he has a trunk line. A lot (most?) residential splits installed in the last 10-15 years don't. The outlet from the air handler goes to a distribution box. Individual flex supply lines come off of the distribution box and go directly to a diffuser without branching again.

Ideally, that distribution box is centrally located, and the branch lines are relatively equal in length. Due to friction losses and restriction, the longer lines will see less air than the shorter ones will.

Which is why what Chris said about the shortest lines getting the least air doesn't make any sense. I would suspect there's a damper or other restriction in those lines if that's the case.
 
You are correct Shawn. The blower is in the attic. Two maybe 14" hoses go out from the unit (one out each side of the) to the returns in each ceiling.
Then one smaller maybe 10-12" line leaves from the top of the unit, runs maybe 10 ft of hose to the distribution box. The dist. box is maybe 12"T x 20"W x 36"L. From there 6" hoses run all over the attic floor out to the vents.

I'm starting to think I'm missing something somewhere. There has to be another dist. box somewhere maybe in the 1st floor ceiling. I need to go up there tomorrow and take a better look. There would have to be in order for the temps to differ from the outlets up and down stairs.

This house was built in '98. It was obviously built as cheap as possible. I can only imagine that the HVAC system is the absolute bare minimum required to cool the house. The unit outside is the size of a small window unit.
 
The distribution box is almost centered in the footprint of the house and you said Shawn. My theory for why the rooms have unequal air blowing out: You have a rectangle with an inlet on one end and 4 outlets down each side. Air is blown into the box at high speed. I think it blows right out the shortest length ducts that also happen to be the vents at the far end of the box. Since there is little resistance in the last two ports it blows right across the other 6 ports and maybe even acts like blowing on the top of a straw. It could even be drawing air out of the room. The solution would be to restrict the 2 vents in the far end of the box. I would think but it made no difference. Even with those vents closed all the way to where they make an awful whistle, the other vents gain nothing.
 
When u check your temp drop you need to take your return reading at the unit since you have 2 different returns with very different temps they will mix. So to get accurate reading need a mixed air temp at the unit. Then check your supply temp and see if you have 18-20* if you really only have 8-10 then more than likely you are low on freon. Or have internal problems with compressor or reversal valve being insuffciant. (Most likely freon though). If you have elec heat make sure one of the strips is not stuck on. Need to check amps to be sure. Ran across this early this summer. Sequencer went bad and one stage of heat was running non stop and they had a 10* temp drop. Duct may very well be wrong or unit undersized but you should still have correct temp drop. Unit is only going to move a max cfm even if duct is to big so drop should be close to right. If duct is to small you should actually have a larger temp differential due to less air coming in contact with coil. So still wouldnt explain 8-10* drop. I dont size duct everyday and not sure what size your unit is but one 12" supply duct dont sound right you should have least 1 more. You have 2 14" returns so even at higher pressure doubt 1 12 is enough. Do you have a run coming out bottom of plenum going down a chase or closet to the first floor. Also almost never does a single zone system work well in a 2 story home. The loads are very different so very difficult to have both areas same temp with 1 thermostat and system.

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