Air Conditioner doesn't seem to be cooling upstairs

[Nick]

Before I call an HVAC technician, maybe someone here has some ideas.

I have two zones in my house, upstairs and downstairs. Each zone has it's own condenser and air handling unit.

The upstairs air handling unit is in the attic and the vents run in the interstitial spaces between the joists. In the downstairs they run below the floorboards in the basement.

My downstairs seems to cool just fine, but the upstairs doesn't seem to be cooling. I do'nt have a thermometer but I put my hand up to the vents and the air flow is cool (not cold) and just very light. Downstairs the air seems to have a lot more pressure out of the vents.

So far to troubleshoot I have checked the condensor outside - nothing is blocked and I don't see any icing up anywhere. I have also replaced the filters upstairs fairly often. Last time was about six weeks ago, but I pulled it and it still looks like it's in pretty good shape. I don't even know where to check for icing on the air handling unit.

At night, it does seem to cool down. But I'm guessing this is why my electric bill is so damn high. During the day, particularly when temps are > 85 or so, it just doesn't seem to be able to keep up.

I don't remember it always having this problem, but it has been this way for about a year. The house is five years old and the AC units (I think they are Tranes) are about the same.

Any ideas? Do I need a real tech here?

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[andrec10]

I would have them serviced. We have ours serviced once a year and have never had a problem.

 

[Edd]

Nick, could you post what the solution was when it gets figured out? I'm curious.

 

[Puck it]

Is the fan spinning on the condenser outside? This will allow the system to cool but not cool to its maximum when the heat is on. Is the system draining water from the unit in the attic?

 

[Nick]

The fan is spinning on the condensor outside. Basically non-stop.

It did cool down last night over night, it seems like it is running OK this morning. It mostly happnes on very hot days. My father in law thinks it might be low on freon on and during the day when it's working really hard it freezes up, preventing some airflow.

I'm not really seeing any water draining but i didn't look for the drain pipe yet on the air handler. My father in law also commented he could "smell" the ice unfreezing through the air. Almost like that moldy smell.

I'll definitely post when I figure it out.

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[o3jeff]

If you do have a moldy smell, get it checked out soon, the mold will wreck havoic on your lungs.

 

[Nick]

I've never noticed it before, but my father in law said it. I change the filters regularly. I'm not sure if it's that or how else to describe the smell, in any event I'm gonig to have someone come this week to look at it.

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[ERJ-145CA]

Last summer my AC compressor wouldn't kick on during real hot days, presumably due to slightly lower voltage from everybody's AC running. The fan would spin outside but the actual compressor wouldn't start. After some internet research I figured I'd try a "hard start kit". It is basically a big capacitor that gives the compressor an extra jolt to get it started. I ordered one over the internet, around $30, and hooked it up to the start capacitor as stated in the instructions. My compressor has worked flawlessly since then, even during those super hot days we had a couple of weeks ago. I figure I saved myself at least a few hundred bucks.

 

[Glenn]

I'm not an HVAC tech...I just ask the tech a lot of questions when they come to visit. We had our system replaced 4 years ago; new compressor outside, new air handler in the attic.

When the old one was on it's way out, I had it charged. I was having a very similar issue; ran a lot, not much cool air. The tech told me a good way to tell if the system is up to snuff: Measure the temp coming out of the vents. It should be at least 15 degrees cooler than the temp in the room. If it's not, it's low on charge or something else. We have a little Radio Shack thermometer that measures outside temp. I'll grab that an put the probe into a vent when the unit is running. I give it a few minutes before taking the reading. I'm not sure if the 15 degree thing is a hard and fast rule, but it seems to be accurate.

Another thing to check will be outside unit itself. The air coming out of the top of the condensor should feel warm compaired to the air temp. If it's just blowing regular ol' air, there could be a charge issue. Whenever our system was low, the outside unit wouldn't be all that warm. I stood outside with the guy when he charged it and you could feel the air getting warmer.

If you want to get into it, you could head up to the attic. Given the temps this time of year, do that early in the AM or later at night. It's brutal up there. The air handler will have a side pannel or two that you can remove to expose the fan and the coil. If you're not getting must air movement, I'm wondering if the fan isn't doing it's job. Or, as mentioned, could be some icing.

Regardless, that's a pretty new system. I'm thinking it'll use the new freon. I know that operates on a higher pressure. We had to have a guy come back after our unit was installed. he said the guys were a little gunshy with charging because it's a higher pressure than they were used to.

 

[Nick]

Last summer my AC compressor wouldn't kick on during real hot days, presumably due to slightly lower voltage from everybody's AC running. The fan would spin outside but the actual compressor wouldn't start. After some internet research I figured I'd try a "hard start kit". It is basically a big capacitor that gives the compressor an extra jolt to get it started. I ordered one over the internet, around $30, and hooked it up to the start capacitor as stated in the instructions. My compressor has worked flawlessly since then, even during those super hot days we had a couple of weeks ago. I figure I saved myself at least a few hundred bucks.

Haha, sounds like a defibrillator for an A/C unit.

I've got the technician coming out this afternoon. I was happy to hear from him the diagnostic charge is only $50. We'll see what he says.

 

[Nick]

I'm not an HVAC tech...I just ask the tech a lot of questions when they come to visit. We had our system replaced 4 years ago; new compressor outside, new air handler in the attic.

When the old one was on it's way out, I had it charged. I was having a very similar issue; ran a lot, not much cool air. The tech told me a good way to tell if the system is up to snuff: Measure the temp coming out of the vents. It should be at least 15 degrees cooler than the temp in the room. If it's not, it's low on charge or something else. We have a little Radio Shack thermometer that measures outside temp. I'll grab that an put the probe into a vent when the unit is running. I give it a few minutes before taking the reading. I'm not sure if the 15 degree thing is a hard and fast rule, but it seems to be accurate.

Another thing to check will be outside unit itself. The air coming out of the top of the condensor should feel warm compaired to the air temp. If it's just blowing regular ol' air, there could be a charge issue. Whenever our system was low, the outside unit wouldn't be all that warm. I stood outside with the guy when he charged it and you could feel the air getting warmer.

If you want to get into it, you could head up to the attic. Given the temps this time of year, do that early in the AM or later at night. It's brutal up there. The air handler will have a side pannel or two that you can remove to expose the fan and the coil. If you're not getting must air movement, I'm wondering if the fan isn't doing it's job. Or, as mentioned, could be some icing.

Regardless, that's a pretty new system. I'm thinking it'll use the new freon. I know that operates on a higher pressure. We had to have a guy come back after our unit was installed. he said the guys were a little gunshy with charging because it's a higher pressure than they were used to.

Yeah, I've been up in the attic. Another thing I noticed about the attic is that I have soffit vents but no real top vents. I can't see a ridge vent (although they did cut the plywood at the peak to accommodate one, it feels like foam up there) and there are no louvered gambrel vents.

So I was wondering generally if the lack of airflow through my attic might have anything to do with the temp. The ducts are just layed out in the attck and while they are wrapped it only says R-5. So I wonder if the ducts are just losing air temp to the attic before it even makes it into the house. I don't think that's it though, as the runs aren't all that long.

 

[Geoff]

Sort of on-topic:

I had a 19 SEER Fujitsu mini-split installed in my cottage last May. It uses DC inverter - variable speed technology. I've been running it 24x7 since the hepa filter has totally solved my allergy issues. My electric bill is half of what it was when I had window air conditioners.

 

[o3jeff]

Can't really find a good pic, but they do use this a lot and put shingles over it on the ridge. Probably what you have.

 

[Glenn]

Yeah, I've been up in the attic. Another thing I noticed about the attic is that I have soffit vents but no real top vents. I can't see a ridge vent (although they did cut the plywood at the peak to accommodate one, it feels like foam up there) and there are no louvered gambrel vents.

So I was wondering generally if the lack of airflow through my attic might have anything to do with the temp. The ducts are just layed out in the attck and while they are wrapped it only says R-5. So I wonder if the ducts are just losing air temp to the attic before it even makes it into the house. I don't think that's it though, as the runs aren't all that long.

Our house was built in the mid/late 1960's. We have a ridge vent, one gable vent...no soffet vents. Our system blows nice and cool, so it's certainly not your attic.

Ridge vents now don't stick up off the roof like they used to. They cut the hole and pit what feels like a Scotch Brite material over the hole, then cover those with shingles. There's another version called a "Cobra Vent"

http://www.google.com/search?um=1&h...l0l0l0l1l172l172l0.1l1l0&ie=UTF-8&sa=N&tab=iw

 

[Nick]

Can't really find a good pic, but they do use this a lot and put shingles over it on the ridge. Probably what you have.

Yeah, that must have been it. I held a match up to it and it didn't seem like it was drawing anything. Seems like it doesn't allow for much airflow, but then again I also went in the attic later in the evening after the sun had set. It does look / feel like that underneath, kind of spongy.

 

[o3jeff]

Yeah, that must have been it. I held a match up to it and it didn't seem like it was drawing anything. Seems like it doesn't allow for much airflow, but then again I also went in the attic later in the evening after the sun had set. It does look / feel like that underneath, kind of spongy.

Maybe go walk the roof to confirm it!:wink:

 

[Nick]

Maybe go walk the roof to confirm it!:wink:

Meh it kind of freaks me out. I'ts a 45 degree pitch and the back drops off almost three stories because I'm on a hill.

 

[Nick]

Well the guy came today. he told me they have overcharged the freon by 3 pounds. I don't know how much that is. Seems to be cooler upstairs, but that's probably also partially due to the fact that it's a little bit shady outside.

 

[Glenn]

Interesting! Thanks for the update. Sometimes too much of a good thing...can be a bad thing. Glad you got it sorted out.

I was in the attic last night putting some stuff away. Found some small leaks in the flex ducting where it meets the trunk duct...got out the ol' foil tape!