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Old 02-16-2015, 11:55 AM   #1
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Problem with heat pump in cold


First heating season in new house. Last two nights have been 0'F or close to it. Our heat pump will not maintain or even come close to set point of 72'. Saturday night it was 60' and Sunday night it was 64' (we supplemented with 3 - 1500w space heaters. Have had the outside unit freeze up completely (a month or so ago with single digit temps) and about 1/2 way frozen over currently. (which leads me to believe it is under charged).

We have R-19 walls, R-38 ceiling. 1900 sf ranch with full basement below. Basement perimeter is half Fox-block R-22 equivalent and half framed with R-19. We have an Ameristar M4AH3036A/B heat pump and air handler combo. 3 Ton unit. Fan speed is wired to medium currently. Air handler is in basement and has 15kw aux. heat package.

Notes:
Air velocity coming out of vents has always felt like a trickle. It barely lifts a piece of paper when placed over the vent. The return vents can barely hold a piece of paper.

I took the blower acccess panel off to make sure it was working and noticed a peice of insulation from the panel was sucked up to the blower. I removed it.

While panel was off i changed it to high speed setting on the fan. Went to check duct velocity and noticed a huge increase, but then realized i forgot to put access panel back on (this is bypassing filter). I let it run this way and within 2 hours it was back up to set point (from ~60 to 71).

Put panel back on and noticed a drop in duct velocity almost back to normal.

Changed filter, no difference.

It is under warranty, and I called my builder who called his hvac company and they are 2 days out on service calls. But said in the mean time I should switch to emergency heat which I dont completely agree with. and after 1 hr of running it has not moved from 64'.

My thought: there is a blockage in the return ducting.

Any help would be appreciated.

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Last edited by akjose; 02-16-2015 at 12:08 PM.
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Old 02-16-2015, 02:04 PM   #2
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Sounds like the defrost module is not working. What kind of filter are you using?

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Old 02-16-2015, 02:10 PM   #3
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Filter is a honeywell 10 FPR 1" filter. Only one i can find that is 18x20x1.

When it does freeze up, it seems like it stays in defrost for a very long time. which is where all of the heat is probably going from the Aux. heat.

It is now up to 71' after using only emergency heat since 11 am today (4 hours).

Last edited by akjose; 02-16-2015 at 02:14 PM.
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Old 02-16-2015, 03:16 PM   #4
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Go with the emg. heat till the techs get to you. To me it sounds like a return air problem.You take off the panels and get airflow.
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Old 02-16-2015, 08:05 PM   #5
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How much airflow should I have through vents (approximate)? If i hold my hand above the vent at arms length (32" from floor) I can not feel any air. maybe a small small amount if any. Should I be able to feel some at that height. I wish I had an anemometer to at least get a static reading.

When i open the panel and short circuit it, i can feel a rush of air even on medium fan speed.

From my old home, i was use to feeling the rush of air...at least see a curtain or two move. I have one curtain that will fill up with air here but it will not necessarily move...barely balloons out.
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Old 02-16-2015, 08:21 PM   #6
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you need a larger amount of return air volume. This is proven by the increase in air flow with the panel off. Simple physics
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Old 02-17-2015, 07:47 PM   #7
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Makes sense...

Supply main branch line off of trunk from blower is 16x8

Return main branch line going into trunk at blower is 14x8
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Old 02-18-2015, 05:34 AM   #8
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If your heat pump is at one end, and you have a single 16x8 supply trunk line, its barely big enough for 2 tons. And the return drop at 14x8 is almost good enough for 1.5 tons.

Pics of duct system would help.
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Old 02-18-2015, 06:12 AM   #9
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Yes. Air handler is essentially at one end. Central plenums. 15' run to one end and about a 40' to the other end'. 6" flex duct from center plenum to exterior walls.
Return is essentially the same, just has shorter branches off of it and utilizes the joist spacing.

I'll take pics later today.
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Old 02-18-2015, 06:23 PM   #10
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Most of the system


Supply on right








4 supply duct to this one main in a 24x35 open area. Another two supply ducts in bedroom at other end of house to. Similar dual return in wall


Other returns are single cavity returns. 1 has 1 supply, the other has 2 supply.


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Old 02-18-2015, 10:29 PM   #11
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Since the trunk line runs in 2 directions. It can move more air in the supply then just 2 tons. Your drop is still undersized. Should have been a 12x20.
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Old 02-21-2015, 08:53 PM   #12
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you could add a small 12x12 return in the return duct by the unit in the unconditioned space that would raise your static pressure and circulate air in the area thats not conditioned space witch would also help with moisture control if the space is not conditioned
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Old 02-22-2015, 09:28 AM   #13
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There are 6 ducts run in the basement. They are closed off right now. I was considering adding the return after reading everyone's input about the undersized returns.

When the basement is finished, I have considered adding a second system for the basement and removing the supply ducts that are currently feeding the basement.
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Old 02-22-2015, 10:38 AM   #14
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Should fix your current duct system before you finish the basement.
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Old 09-09-2015, 03:28 AM   #15
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Updates:
Been a while since I updated this so here is my hair-pulling experience: it is sad when I one can post pics online and give a little information and the suggestions from the online community are more precise than the hvac installer.
Fast forward to a day it was 70 degrees and very sunny. I Had the windows open all morning and noticed I was feeling warm, when I looked at the inside temp it was 74, I closed the windows and turned on the AC. After it reached 78 I called a local tech who lives 3 miles away because I knew there was no way to get these other yahoos out being close to 5pm when they would t even come out in an emergency.
So, during his inspection we found absolutely zero refrigerant in the system. He also told me his opinion was it needed more return and we discussed where it would go. He also told me, which I already knew, no flow means bad, must have airflow to have temp change. We also looked for leaks but couldn't find anything noticeable.

So the hvac installer company comes out, first they charged the refrigerant but couldn't get it to where it needed to be however said it should be good enough....didn't really spend too much time looking for leaks though, I guess they think it just evaporates on occasion.

On the no airflow issue, They told me that even though there is no airflow it may seem like the system is not working but the system is still working. I argued some but gave up after a while of getting nowhere. Of course, the day they came out it was beautiful 70 degrees and overcast so there was no load on the system.

Then comes warmer weather, unit couldn't keep up in 80 degree weather. Once again it was low on freon, not out just low.

I did a complete ventilation survey with 4" anemometer from work. While I know it is not exact, I measured 706 cfm for a 3 ton system., but I can't imagine I missed 500 cfm of air anywhere.

After calling my builder and convincing him I needed a new return cut in upstairs and that something else was wrong with the system because it is magically losing freon.

He set up the hvac "pros to come out one day which I couldn't be home for, after 3 hours of testing they diagnosed a bad reversing valve and also found a broken solder inside the outside unit. It was actually the other guy I had called that found it but we couldn't tell what it Was or where it came from, I just mentioned it to them and they said that was the problem with it losing freon.

My builder walked them through everything I talked about or showed him about the fan access panel having so much pressure on it, and I typed him a big letter explaining all of my findings as far as air flow goes.

It took the owner of the company to come out to say it needs more return.

So after they left with their chests puffed out from conquering the issue and the owner of the company making an appearance to help out, and even a 2 hour phone call to Trane. And cutting in another return where I told them to put it. They also put a return on the main vertical return trunk(I would have preferred this on the bottom of the trunk to completely open the whole system and allow it to flow more). The system works much better now.

It has consistently kept a temps cooler, our electric bill went from a $600 average from jan to May to a $60-80 summer month bill. The only time it doesn't work now is if the outside temp is above 90. Granted it still should work.

Now there only excuse when it doesn't work is that the system wasn't designed to operate in the extreme temps and 90 is an extreme design temp for the area.

It is upsetting when the first thing you think about when planning a birthday party for your daughter is, I wonder if my hvac is going to handle the load of all these people. This past weekend we had 30 people over, and it was 88 degrees outside, setpoint of 72 and it was 78 inside at one point.

So on to my new venture because I have exhausted all means short of changing out the entire duct system. I think I may use two of the supply registers supplying the basement and flip the over to supply the main floor instead.
I don't think I ever mentioned this part, the main area of my house is a 24x35 room with 14' cathedral ceiling with huge windows on the westward side. This has 4 supply (4x10) and had 1 double wall space return. Now it also has a 10x14 floor joist return as well on the opposite side of the room from the other return. But I think I am maxed out on quantity through those 4 supply's. If I had two more supplys from the basement, then it should be enough to cool and heat adequately I. That space.
All the bedrooms seem to be fine as far as quantity and comfort goes.

My only concern is, if I currently have the basement vents closed, then How much more air am I going to get from them if I flip them? Especially if the return line is already about maxed out in that area.


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