Stubborn Condensation Leak on A-Coil

We've got an Improperly draining A coil in an American Standard downflow fan coil unit. Drain is clear.
Maintenance guy allowed to filter to clog and no doubt some initial dust clogging the coil.
It's been cleaned twice with green Diversitech light foaming cleaner from Michel.

Condensate leak stopped and then started leaking again after a month.

Is there a better or more effective coil cleaner worth trying?

Anything else besides cleaning which could suddenly cause this 8 yr old system to develop a condensate leak?

Fan is variable speed (non adjustable) and air flow does not seem to be an issue.

Is the coil leaking, is the drain line plugged, is water blowing off the coil? Those questions need to be answered before a cure can be found.

Drain is clear. Best we can tell, condensate may be blowing off the coil, or just draining improperly....potentially due to some area still lightly clogged. Perhaps there could be another cause.

One tech guy says he uses a piece of plexiglass to diagnose. I suppose this suggests that he uses plexiglass in place of the access panel, and tapes that off to establish normal air flow. Have not seen it done.

Coil cleaning did clear up the problem for a month,,,,,but now it's returned.

I would not think that a coil, properly cleaned, would get dirty enough to be a problem in a month, unless you don't use filters and live in a dust bowl. Did the tech check the charge? If a unit is under charged it will get "hot spots" in it. No, it's not really hot but is a few degrees warmer than the rest of the coil. This changes the surface tension of the coil so water stacks up there, where it eventually drips off. I would call the tech that temporarily replaces the panel with the plex to see what's going on inside, it sounds like he may be pretty sharp.

The R-22 charge is perfect.

I'm guessing that leaves us air flow to consider or perhaps another brand or type of coil cleaner.

There initially was a fair amount of small rust like debris in the pan. Since the fins are aluminum and the coil is copper tube, one wouldn't think there's something about the bits of rusted metal that might be contributing to this? Nothing is obvious thus far.

Is there a better or more effective cleaner that the green Diversitech concentrate sold by RE Michel?

This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

You can find the rules for posting and qualifications here.

Additional infractions may result in loss of posting privileges.

The plexiglass door provides a way for the tech and/or you to watch the unit as it runs to see if condensate is blowing off the coil.

Condensate blowing off a coil is either too much airflow, debris on the coil fins causing water to collect and blow off vs. running down into the pan, or excessive static pressure. Since you've cleaned the coil, I would refocus on the other two potential causes.

Thorazine


This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

You can find the rules for posting and qualifications here.

Additional infractions may result in loss of posting privileges.

I appreciate the previous helpful suggestions!

This was with the 8 year old 2 ton A/S counter flow fcu in cooling mode

The plot thickens....

The coil has been cleaned again and the underside has been blow out carefully with compressed air. Without effect.

Techs have worked on this unit three times and have no clue.

Installing plexiglass instead of the lower door cover, we see the leaks! It's not the drain pans. The condensate drips are coming from the underside of the coil (it's downflow with the coil on top) The drips are coming from one or two single rows representing the copper tubing running horizontally in the coil about 1/4 of the way from the top of the A. (Maybe 4" down from the top)

There is some condensation drips from the opposite side of the coil at about the same height....but much more on one side than the opposing side.

As mentioned earlier the R-22 pressures were checked recently and may need to be checked again. Does this sound like a refrigerant issue?

We've yet to experiment with the variable speed motor speeds. Not sure if more or less fan speed might be helpful.

Quote:

---

Originally Posted by etbrown4

I appreciate the previous helpful suggestions!

This was with the 8 year old 2 ton A/S counter flow fcu in cooling mode

The plot thickens....

The coil has been cleaned again and the underside has been blow out carefully with compressed air. Without effect.

Techs have worked on this unit three times and have no clue.

Installing plexiglass instead of the lower door cover, we see the leaks! It's not the drain pans. The condensate drips are coming from the underside of the coil (it's downflow with the coil on top) The drips are coming from one or two single rows representing the copper tubing running horizontally in the coil about 1/4 of the way from the top of the A. (Maybe 4" down from the top)

There is some condensation drips from the opposite side of the coil at about the same height....but much more on one side than the opposing side.

As mentioned earlier the R-22 pressures were checked recently and may need to be checked again. Does this sound like a refrigerant issue?

We've yet to experiment with the variable speed motor speeds. Not sure if more or less fan speed might be helpful.

---

This is what I was talking about in my earlier post {#4}. Coils have a surface tension that holds the water to the coil so it runs down and not form droplets. If the entire coil is not feed with the right amount of refrigerant it gets a "hot spot" in it. When this happens you see water running down to the hot spot where it builds up and finally drops off. When th ecoil is cleaned the detergent leaves a residue that has a sheeting action for th ewater so it works for a short time till the residue rinses off. It seems more prevelant in downflow units. Every time I ran into it the unit was low on refrig. and the "hot spot" was on the last pass. These were all slope coils, not sure if your is a slope or "A". You may be low or you may have a bad distributor tube or flow control device {TXV or fixed}

Quote:

---

Originally Posted by kls-ccc

This is what I was talking about in my earlier post {#4}. Coils have a surface tension that holds the water to the coil so it runs down and not form droplets. If the entire coil is not feed with the right amount of refrigerant it gets a "hot spot" in it. When this happens you see water running down to the hot spot where it builds up and finally drops off. When th ecoil is cleaned the detergent leaves a residue that has a sheeting action for th ewater so it works for a short time till the residue rinses off. It seems more prevelant in downflow units. Every time I ran into it the unit was low on refrig. and the "hot spot" was on the last pass. These were all slope coils, not sure if your is a slope or "A". You may be low or you may have a bad distributor tube or flow control device {TXV or fixed}

---

When you say 'last pass' do you mean the highest loop of copper tubing in a coil.

This is an A coil and the condensation droplets are forming in possibly the 2nd loop of copper tubing from the top, or about 4" from the top of this a coil. We are getting condensation of both opposing sides of the A coil at that height. (though more on one side than the other. Again, it's on the underside) Would this meet your description of the 'last pass'?

From your post, it sounds A) undercharged, or B) possibly a bad distributor tube, or C) a bad TXV. Other than checking the pressures, how would you diagnose this further?

"Last pass" refers to how the refrigerant passes through the coil. Depending how the coil is made it could be anywhere you just have to look at how the tubeturns are placed and follow it through. However it may not be the last pass, it will depend on how far the refrigerant gets through the coil before all the liquid is gone.

As far as diagnostics, get yourself a good tech. Far to many variables to try and decifer on a computer screen. Also if it's low on refrigerant, where did it go? Another reason you need a "good" tech.