Unique issues causing coil to freeze.

[Prowelder]

FEM4X6000BL4E

[Saturatedpsi]

If we assume (ass-u-me) the system wasn't frosting up with the old air handler, then logic would suggest there's something about/with the new air handler causing the issue...as Knave already mentioned.

My personal unproven theory is all heat pumps do the same thing...they are all designed to meet the AHRI standards and I'm confident each mfg designs for the minimum cost to achieve AHRI certification. Some of them may have found a way to tweak this or that to save a dollar or get another 500 Btu capacity or another 200 cfm of airflow. And the tweaking might require "matched" components.

Still, your ICP air handler should blow enough air if the ductwork is adequate...but maybe it's not. I've never had a lot of confidence in static pressure measurements or at least, the accuracy of the measurements. I would consider them as a rough estimate.

As already mentioned several times, the system isn't doing the 350 CFM per ton design minimum which is a fact based on saturated evaporator temps. And I (we) don't know what the particular blower performance numbers are...maybe 0.6 (or more) is too much.

Return "boxes" add a lot of "effective length" to duct geometry if there aren't any turning vanes to reduce turbulence. If the box has none, that's a fairly inexpensive modification to make which would improve airflow. You could install vanes in the supply duct as well.

If the problem isn't duct related then maybe it's in the blower motor or control...is it an X-13? They are notorious for funky performance and new ones aren't necessarily exempt from being funky. But you got to be there when it funks...or get the data logger.

Someone mentioned closing off the basement ducting...personally I think that would worsen the situation...XXX cfm of 5˚ cooler air is better than reducing the total air volume XXX cfm.

All that said, if the freeze stat works and the HO is happy, let it ride...

[knave]

The basement is cold enough that the mixed RA temp is 12° colder than main level. Something is off.

[Prowelder]

I agree about the basement being so cold, I know basements stay consistently 65 degrees and add a little mechanical cooling and it goes down quickly. I grew up with a basement. However I don’t think it’s so unusual to be 10 degrees colder in the basement from upstairs. When air conditioning hasn’t been running and house has heated up.

[knave]

Be sure it’s not recirculating any cool air to returns.
Double check blower speed and rotation. Compare blower amps to FLA.
If blower shuts off on thermal it will freeze.
Check the system late in the afternoon, when outdoor ambients may be lower but home is still heat soaked.
Spend an hour just watching it run, find all the returns, see if they’re plugged with lint or covered with clothes.
Redo your numbers. How did you end up with Exactly 10° subcooling down to the .1°?

[knave]

and that’s all I got.
Unless you live near me in which case I would go there with you.

[Prowelder]

It wasn’t exact, it was actually 10.1 on Fieldpiece Sman 460. I don’t know how to post pic so I just copied numbers. Hope y’all aren’t holding .1 degree against me

[knave]

It wasn’t exact, it was actually 10.1 on Fieldpiece Sman 460. I don’t know how to post pic so I just copied numbers. Hope y’all aren’t holding .1 degree against me

Lol of course not

[Prowelder]

I have been working on it in the afternoons when house is hot and outdoor ambient temps are falling. I have spent lots of time watching it run already. Checked every vent and return in the house looking for those things and didn’t find any. I would love for someone to be close and willing to go by with me.

[knave]

One more thing, last summer I had a service call at a meat shop. Needed a new a-coil, got a generic ADP coil that matched the tonnage of the condenser. I put a R22 piston in it. But I was shocked. The old coil was WAY bigger, and sure enough, the SST ended up being lower and very near freezing. It would have been better for me to get a coil 1/2 ton bigger. That said, I understand you likely didn’t have that option since it’s already a 5 ton.

[Prowelder]

I could see that, and yes my options there are zero.

I’ve dealt with freezing coils and dirty condensers, and equipment not properly maintained and mismatched before and this is the worst situation I’ve been in to date.

[knave]

You really should convert it to 407C
:-)

[Prowelder]

I’ve done plenty of that too! How’d you know what I as gonna try next?? You reading my brain or something?

I’ve had to do a lot of questionable things to systems by direction of the company I worked for.

[Saturatedpsi]

FEM4X6000BL4E

Based on some information I found for that model, the motor is a "high efficiency" ECM (?). The other motor options for other models are ECM and Variable speed. Got no clue what the difference is between "high efficiency" ECM and just ECM.

The blower performance chart shows 1736 CFM for tap 5 (high speed) @ 0.6 static.

If your 0.6 static measurement was accurate, the blower should be doing 347 per ton which would be design minimum. But based on some expanded data for a different brand the evaporator saturated temp would be a few (3 or 4) degrees higher depending on wet bulb temps. So, IMO it ain't doing the 347.

You might confirm Tap 5 is actually connected at the motor for high speed...and since the motor is some variation of ECM, consider it as a possible cause of the problem.

[Prowelder]

Ok I trust your math, it’s doing minimum airflow but still at design airflow. Shouldn’t make coil a block of ice at design minimum.

I put it on high myself and it’s actually tap 3 on this particular motor according to wiring diagram on motor.

[NTX]

Based on some information I found for that model, the motor is a "high efficiency" ECM (?). The other motor options for other models are ECM and Variable speed. Got no clue what the difference is between "high efficiency" ECM and just ECM.

The blower performance chart shows 1736 CFM for tap 5 (high speed) @ 0.6 static.

If your 0.6 static measurement was accurate, the blower should be doing 347 per ton which would be design minimum. But based on some expanded data for a different brand the evaporator saturated temp would be a few (3 or 4) degrees higher depending on wet bulb temps. So, IMO it ain't doing the 347.

You might confirm Tap 5 is actually connected at the motor for high speed...and since the motor is some variation of ECM, consider it as a possible cause of the problem.

That motor is an X-13. Carrier (and apparently ICP) rather confusingly market their X-13s as "high efficiency ECMs" and their variable speed ECMs as either "ECM" or "Variable Speed."

I agree with Saturatedpsi that you need to be on tap 5, not 3. Product Specs Check page 8, on tap 5 at 0.6 static, you get 1736 CFM, but at tap 3, you only get 1655 CFM.

I came across an explanation of how Carrier programs their X-13s in a fan coil service manual sometime back. They call their X-13 motor taps Low (1), Medium (2), and High (3). Those 3 taps have 90 second blower off delays programmed in. Tap 4 is the designated Electric Heat tap - same speed as Tap 3, but with no blower off delay. Tap 5 is a "Max" speed for high static situations, it is higher speed than Tap 3 High but has no blower off delay. I would try Tap 5 and see if that helps. Good luck.

[Prowelder]

Well that explains a lot. I’ve been told before tap 5 for high but wanted to check motor and verify tap speeds and it said 3. That would make a lot of sense if it is keeping the blower on delay for 90 seconds that coil is probably getting frosty before it ever has a chance to move any air and then moving less air than it needs. That would explain it all! Thanks so much!

[NTX]

No worries, glad I could help. The programmed blower delays are off delays (after cooling call ends), not on delays (at start of cooling call), so the presence or absence of the delay shouldn't affect the coil freezing/frosting. But the lower airflow on tap 3 vs. tap 5 might be enough to cause it. I'm not completely certain, I'm still fairly green, hopefully one of the really knowledgeable and experienced guys participating in this thread can tell us if 81 less CFM would be enough to cause your frozen evap.

[Prowelder]

Ahh, I misunderstood. It was said earlier with .6 static I’m slightly below design minimum airflow ( don’t recall actual number) so 81 more cfm may just be enough to make the difference. Like you said maybe one of the more experienced will confirm this for us.

[Saturatedpsi]

..been two weeks since your original post. Is it still frosting up? Every day or just sometimes?