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Buzzant
06-01-2010, 02:14 AM
Hi every one
Me again!
I have a Mitsubishi Mr.Slim heat pump 15 000 BTU and there is a formation of ice in the bottom of the exterior unit that seem to go through the coil.

is that normal and can that effect it?

Thanks

Magoo
06-01-2010, 05:01 AM
In a word "yes ". That would be normal considering where you live. The ambient temps that system operates in winter, the out door coil would develop ice.

yangchenchen
06-01-2010, 09:09 AM
When the ice forms to some extent, the unit will start to defrost, the ice will disappear.

Argus
06-01-2010, 11:18 AM
.


Ice on an exterior Air-Source heat pump unit in the heating mode is normal when the ambient temperature falls, as a rule of thumb, below about 6 degrees Celsius. Above that temperature you should see a coating of moisture.

Having said that, whatever the pick up is, it should be evenly coated across the whole coil and should, on a correctly sized unit in good mechanical health, be completely removed periodically by the automatic defrost cycle. The defrost reverses the flow for a short time so that the outdoor coil receives heat as it would when the unit is cooling.

Whatever it's doing, the heating efficiency of the machine is definitely affected by parts of the coil being out of service due to ice formation.

What's the cause?
If you have a coil that is going through a series of regular or prolonged defrost cycles and still leaves a belt of ice at the base of the unit that does not get removed, I would suggest that your unit may have a slight deficiency of refrigerant, probably a small leak somewhere.
Not enough to noticeably impair the operation, but enough to compromise the defrost.
When a defrost occurs in these circumstances, the water runs off and re-freezes on the lowest part of the coil that does not get the full heating effect due to insufficient refrigerant.

If this is the case, you will need professional help. The refrigerant charge quantity in these units is a precise amount by liquid weight - to get it right, you can't just add a squirt, too much is a bad as too little. The type and weight of refrigerant will be available in the manufacturer's literature or on the data plate of the unit.

I'd recommend getting the charge professionally checked - if it is running short of refrigerant, long term this can cause serious, expensive damage.




.

desA
06-01-2010, 11:25 AM
^ Excellent post. Very well summarised. :)

VRVIII
06-01-2010, 12:24 PM
.


Ice on an exterior Air-Source heat pump unit in the heating mode is normal when the ambient temperature falls, as a rule of thumb, below about 6 degrees Celsius. Above that temperature you should see a coating of moisture.

Having said that, whatever the pick up is, it should be evenly coated across the whole coil and should, on a correctly sized unit in good mechanical health, be completely removed periodically by the automatic defrost cycle. The defrost reverses the flow for a short time so that the outdoor coil receives heat as it would when the unit is cooling.

Whatever it's doing, the heating efficiency of the machine is definitely affected by parts of the coil being out of service due to ice formation.

What's the cause?
If you have a coil that is going through a series of regular or prolonged defrost cycles and still leaves a belt of ice at the base of the unit that does not get removed, I would suggest that your unit may have a slight deficiency of refrigerant, probably a small leak somewhere.
Not enough to noticeably impair the operation, but enough to compromise the defrost.
When a defrost occurs in these circumstances, the water runs off and re-freezes on the lowest part of the coil that does not get the full heating effect due to insufficient refrigerant.

If this is the case, you will need professional help. The refrigerant charge quantity in these units is a precise amount by liquid weight - to get it right, you can't just add a squirt, too much is a bad as too little. The type and weight of refrigerant will be available in the manufacturer's literature or on the data plate of the unit.

I'd recommend getting the charge professionally checked - if it is running short of refrigerant, long term this can cause serious, expensive damage.
.

Very detailed post Argus, I would also like to suggest another possibility.
Most manufactures will specify that the outdoor must not be raised from ground level to allow adequate drainage during defrost cycle. If this has not been done the ice can gradually build up from the base of unit, when you have continual defrost cycles at ambient temps <0 C.
Some manufactures also recommend an optional (thermostat controlled) heater tape be installed in the unit base, the option is normally recommend where continued low ambient temps are expected.

Argus
06-01-2010, 12:59 PM
.

Thank you DesA.

VRVIII, Agreed.
Adequate condensate removal from the unit is an issue.

However the original poster is in Canada, so I'd expect that to be thought of given their expected ambient and the observation from him was that the ice was right through the coil section.


.

VRVIII
06-01-2010, 01:12 PM
.

Thank you DesA.

VRVIII, Agreed.
Adequate condensate removal from the unit is an issue.

However the original poster is in Canada, so I'd expect that to be thought of given their expected ambient and the observation from him was that the ice was right through the coil section.
.

Ah, I didn’t notice his location :D.
I have friends who live in Saskatoon Canada, there experiencing temps of -25 ~ -35 C. I would think system must be very close to or out of its operation range.

Buzzant
06-01-2010, 01:24 PM
@ argus
it looks exactly like you said, it did a lot of defrost lately and it is a build up in the base, i will contact the installer.

Thank you very much and also thank to every one.

Buzzant
06-01-2010, 02:52 PM
@ argus
it looks exactly like you said, it did a lot of defrost lately and it is a build up in the base, i will contact the installer.

Thank you very much and also thank to every one.


Hi argus
i just spoke with the ninstaller and he suggest that the Hole for the drain must have been block! me i know that the inside was pretty clean but hey what can i say?

he suggest that i melt the ice with hot water.
what are your thouhgt on that?

Buzzant
06-01-2010, 02:56 PM
just to be clearer, the ice is in the bottom and around 2 inches thick, inside and out (both side of the coil)

back2space
06-01-2010, 03:17 PM
just to be clearer, the ice is in the bottom and around 2 inches thick, inside and out (both side of the coil)

If the unit is mounted on the ground it is possible that the drainage hole underneath is blocked i.e leaves that have blown away or simply the water draining away as just frozen as it has.

I would make sure that it isnt blocked and flush away with warm water, not hot as this could cause thermal shock.

Once all is free flowing again just monitor it. WHen it freezes up does the whole coil freeze up? Even the bottom?

Buzzant
06-01-2010, 03:53 PM
If the unit is mounted on the ground it is possible that the drainage hole underneath is blocked i.e leaves that have blown away or simply the water draining away as just frozen as it has.

I would make sure that it isnt blocked and flush away with warm water, not hot as this could cause thermal shock.

Once all is free flowing again just monitor it. WHen it freezes up does the whole coil freeze up? Even the bottom?

My tought exactly, and it is about 2 feet from the ground.

Thanks matehttp://www.refrigeration-engineer.com/forums/images/icons/icon6.gif

back2space
06-01-2010, 04:02 PM
My tought exactly, and it is about 2 feet from the ground.

Thanks matehttp://www.refrigeration-engineer.com/forums/images/icons/icon6.gif

Give us a thanks with the scales next to my name hehe

my unit is mounted on the floor and al sorts of crap can blow against it such as plastic bags and wrappers.

Argus
06-01-2010, 04:24 PM
he suggest that i melt the ice with hot water.
what are your thouhgt on that?




He's trying to eliminate the obvious. But I don't think that it shows much regard for his customer.

The scenario goes like this:

For whatever reason, including the one I gave you, ice collects and does not disperse with the defrost.
It grows bigger each defrost.
It gets so big it blocks the drain hole.
It continues to grow and eventually fills the shallow drain pan, then it may jam or damage the plastic fan blades (more expense).
You eventually complain and gain on the installer until he fixes it


I still think that a constant ice block on the lower few inches of the outdoor coil going right through, even when the rest of the coil is cleared is showing classic symptoms of a slight shortage of refrigerant - as I said, not much but enough to impair the effect of the full defrost.

But, you can humour him and try the water test first, if you can. Tepid water is the way to go, but turn the unit off and isolate the electrics first.

Get everything nice and clean then I suggest that if you have a digital camera handy, take a photo of the offending part and do so at regular intervals each day if you see the ice returning, noting each time if the drain port is clear. You can then present him with the evidence if it recurs and demand that he reclaim the entire charge and weigh in the precise new one.



.

back2space
06-01-2010, 04:27 PM
Yes thats a good idea.

We have over a foot of snow here its -4 outside and I have just checked the unit and its draining away fine, its got snow all the way around and in front of it but its draining fine no ice inside at all just in front.

Buzzant
06-01-2010, 06:36 PM
He's trying to eliminate the obvious. But I don't think that it shows much regard for his customer.


The scenario goes like this:
For whatever reason, including the one I gave you, ice collects and does not disperse with the defrost.
It grows bigger each defrost.
It gets so big it blocks the drain hole.
It continues to grow and eventually fills the shallow drain pan, then it may jam or damage the plastic fan blades (more expense).
You eventually complain and gain on the installer until he fixes it

I still think that a constant ice block on the lower few inches of the outdoor coil going right through, even when the rest of the coil is cleared is showing classic symptoms of a slight shortage of refrigerant - as I said, not much but enough to impair the effect of the full defrost.

But, you can humour him and try the water test first, if you can. Tepid water is the way to go, but turn the unit off and isolate the electrics first.

Get everything nice and clean then I suggest that if you have a digital camera handy, take a photo of the offending part and do so at regular intervals each day if you see the ice returning, noting each time if the drain port is clear. You can then present him with the evidence if it recurs and demand that he reclaim the entire charge and weigh in the precise new one.



.

Excellent idea with the photos, big thanks once again ;)

Buzzant
06-01-2010, 06:40 PM
You know! thinking about it, it could have been blocked by blowing snow then filled up after, i will melt all the ice, fix it up and watch it and keep you guys posted.

back2space
06-01-2010, 06:50 PM
You know! thinking about it, it could have been blocked by blowing snow then filled up after, i will melt all the ice, fix it up and watch it and keep you guys posted.

it is possible while the unit was off that snow could have blown through the fan and then frozen.

Buzzant
07-01-2010, 01:12 AM
Ok guys its done i,v melted all the ice and let me tell you that it,s easier said then done lol
Next i,ll monitor it very closely and give you some feed back.
Once again big thanks to all

mad fridgie
07-01-2010, 01:32 AM
I do not believe that this is that uncommon, the coil sensor I bet is above the ice region. The unit will be defrosting and terminating as it should.
After defrost you continue to get water falling, this can freeze before it all drains away from the coil in cold ambients, over a period this just builds up. As we know one a coil is frozen, it is not going to defrost without a bit of assistance.
I have in the past altered the coil probe position to cover this icing phenomum.

desA
07-01-2010, 02:28 AM
Do these evaps have electric heater strips in the base?

VRVIII
07-01-2010, 10:12 AM
Buzzant,

Can I ask what is the average ambient temp where you are in Canada?

VRVIII
07-01-2010, 11:10 AM
Do these evaps have electric heater strips in the base?


Very detailed post Argus, I would also like to suggest another possibility.
Most manufactures will specify that the outdoor must not be raised from ground level to allow adequate drainage during defrost cycle. If this has not been done the ice can gradually build up from the base of unit, when you have continual defrost cycles at ambient temps <0 C.
Some manufactures also recommend an optional (thermostat controlled) heater tape be installed in the unit base, the option is normally recommend where continued low ambient temps are expected.


Buzzant,

Can I ask what is the average ambient temp where you are in Canada?

As Argus said the ice build could be caused by a slight shortage of refrigerant but if you’re continually experiencing very low ambient temperatures. This could also cause a similar build up of ice over a time period.

After each defrost cycle, water will still be dripping from heat exchanger fins leaving a film of water in the base of unit (no matter how good the drain holes are). The unit base will be =/< ambient temp and the water will quickly freeze when the unit restarts in heating mode. After continual defrost cycles the ice will gradually build up onto bottom of heat exchanger.

The only way to prevent this would be to install heater tape into the unit base.

Buzzant
07-01-2010, 01:41 PM
2 weeks ago it was between -8C and -13C now its -5 but the -13 are comming back this week and the -20's are very close now and that's all without the wind factor.

But like i said i will monitor it very closely.

back2space
07-01-2010, 01:44 PM
I know a couple of people here who put a bit of salt in the bottom of the unit and this stopped it from freezing.

VRVIII
07-01-2010, 02:14 PM
2 weeks ago it was between -8C and -13C now its -5 but the -13 are comming back this week and the -20's are very close now and that's all without the wind factor.

But like i said i will monitor it very closely.

Hi,

If you do take photos during each stage of the ice build up, it might be interesting to post a copy of them.

Buzzant
07-01-2010, 03:27 PM
I know a couple of people here who put a bit of salt in the bottom of the unit and this stopped it from freezing.

Personnally i wouldn't try that cause it could make it rust?


Hi,

If you do take photos during each stage of the ice build up, it might be interesting to post a copy of them.

Hopping i wouldn't have to but it it does come back i will certainly do;)

johnnychin
08-01-2010, 06:43 AM
Yeah. It is better to take a series of photo of the ice form as it never happens in place

Buzzant
08-01-2010, 02:34 PM
i think i now know what happened, 2 weeks ego we had 2 days of freezing rain then the day after, blowing snow and the pump is right under the gutter so it pored water on the cold casing and blowed snow into the unit i can easaly imagine the ice forming in these conditions. i went and put a tick and slippery sheet of plastic over it so now the water wont freeze on and into it.
look i put some pictures.
http://img682.imageshack.us/img682/1509/img6220.th.jpg (http://img682.imageshack.us/i/img6220.jpg/)
http://img686.imageshack.us/img686/7656/img6221c.th.jpg (http://img686.imageshack.us/i/img6221c.jpg/)
http://img189.imageshack.us/img189/7374/img6222r.th.jpg (http://img189.imageshack.us/i/img6222r.jpg/)

Buzzant
08-01-2010, 02:38 PM
Sorry im not that good when it come to uploading pictures

http://img341.imageshack.us/img341/4107/img6220p.jpg (http://img341.imageshack.us/i/img6220p.jpg/)http://img341.imageshack.us/img341/img6220p.jpg/1/w640.png (http://g.imageshack.us/img341/img6220p.jpg/1/)
http://img42.imageshack.us/img42/9813/img6221y.jpg (http://img42.imageshack.us/i/img6221y.jpg/)http://img42.imageshack.us/img42/img6221y.jpg/1/w640.png (http://g.imageshack.us/img42/img6221y.jpg/1/)
http://img42.imageshack.us/img42/7302/img6222o.jpg (http://img42.imageshack.us/i/img6222o.jpg/)http://img42.imageshack.us/img42/img6222o.jpg/1/w640.png (http://g.imageshack.us/img42/img6222o.jpg/1/)

back2space
08-01-2010, 02:39 PM
i think i now know what happened, 2 weeks ego we had 2 days of freezing rain then the day after, blowing snow and the pump is right under the gutter so it pored water on the cold casing and blowed snow into the unit i can easaly imagine the ice forming in these conditions. i went and put a tick and slippery sheet of plastic over it so now the water wont freeze on and into it.
look i put some pictures.
[/URL]
[URL="http://img686.imageshack.us/i/img6221c.jpg/"] (http://img682.imageshack.us/i/img6220.jpg/)
http://img189.imageshack.us/img189/7374/img6222r.th.jpg (http://img189.imageshack.us/i/img6222r.jpg/)

I would take the board off the back of the unit as you are blocking part of the coil there and this will mean the unit will not be collecting heat as efficiently and you will be putting more strain on the compressor.

I would just keep an eye on it and then you can always defrost it manually if it builds up again.

Buzzant
08-01-2010, 03:05 PM
I would take the board off the back of the unit as you are blocking part of the coil there and this will mean the unit will not be collecting heat as efficiently and you will be putting more strain on the compressor.

I would just keep an eye on it and then you can always defrost it manually if it builds up again.

I know it look that way from this angle cause of the pipes casing but believe me there is plenty of breathing room from view from the other side the plastic as a memory so it pop right up right after the pipes casing but i will double chek it, thanks

back2space
08-01-2010, 03:09 PM
I know it look that way from this angle cause of the pipes casing but believe me there is plenty of breathing room from view from the other side the plastic as a memory so it pop right up right after the pipes casing but i will double chek it, thanks

Yeh make sure the entire coil is unobstructed. I would consider having it just flat on top of the unit and putting a couple of bricks on top to stop it falling off.

No need to have it bent on there, water will still come off and any snow on there will be fine.

Buzzant
08-01-2010, 06:43 PM
I can understand putting strain on the compressor, when i am in cooling mode and the out side coil are hot but in heating mode the air outside is already cold so, does a barely noticable restrain will put a strain on the compressor?

me i like to think not.
Your thought?

back2space
08-01-2010, 06:48 PM
Im sure the engineers will be along to confirm but im sure that if not all part of the coil is receiving air flow then it doesnt perform a well.

Is it not possible for you to just put the panel on top of the unit with a brick on top so that it is flat rather than covering the top part of the coil?

Gary
08-01-2010, 07:10 PM
Move the unit away from the wall.

Gary
08-01-2010, 08:09 PM
I can understand putting strain on the compressor, when i am in cooling mode and the out side coil are hot but in heating mode the air outside is already cold so, does a barely noticable restrain will put a strain on the compressor?

me i like to think not.
Your thought?

In heating mode, insufficient outdoor airflow can blow the valves out of the compressor. Airflow through both coils, in either mode, is absolutely essential.

Gary
08-01-2010, 08:18 PM
Hi argus
i just spoke with the installer and he suggest...

Are you saying this was installed by a professional? I think not. I can't imagine a professional installing an outdoor unit right up against the wall like that.

Buzzant
08-01-2010, 08:30 PM
Are you saying this was installed by a professional? I think not. I can't imagine a professional installing an outdoor unit right up against the wall like that.


Maybe it doesn't show on the picture but it's at lease 12 inches from the wall.

Buzzant
08-01-2010, 09:02 PM
Is it not possible for you to just put the panel on top of the unit with a brick on top so that it is flat rather than covering the top part of the coil?

I probably will, i am not home right now

back2space
08-01-2010, 10:48 PM
I probably will, i am not home right now

I certainly would move the panel so its on top as Gary has stated above that you could blow the valves on the compressor due to the increased pressures that lower airflow creates.

Buzzant
11-01-2010, 08:47 PM
Just a follow-up.
It really seem that rain and dripping water was the problem, i even had to go in the addic to properly place the isolation in a few places that cause the ice to melt right over the unit, i cut the protector top plastic (that i made) so it doesn't effect the air flow at all but still protect.
So thanks again and next time i will know what to look for first.