HVAC guys: Coil icing

[Cameramonkey]

So I have a unit that occasionally ices up. Multiple hvac companies cant figure out why. They think the last time it was the txv so they replaced it.

Ive got a backup unit that kicks in and keeps the room at temperature so its more annoyance than anything.

I'm wanting to setup an early warning system so I know its coming. I have a spare temperature probe for my network monitoring system I could deploy inside the unit.

I'm assuming the reason the unit doesnt ice normally is because the coil doesnt get below 32*, correct? So if I attach the temperature probe to the coil, I can monitor the coil temp and get an alert if it ever does get down below freezing? Or am I incorrect?

Hopefully that valve was the problem, but this monitoring solution wont hurt, and wont cost me anything but time. (and a zip tie LOL)

 

[ChristianPatriot]

So I have a unit that occasionally ices up. Multiple hvac companies cant figure out why. They think the last time it was the txv so they replaced it.

Ive got a backup unit that kicks in and keeps the room at temperature so its more annoyance than anything.

I'm wanting to setup an early warning system so I know its coming. I have a spare temperature probe for my network monitoring system I could deploy inside the unit.

I'm assuming the reason the unit doesnt ice normally is because the coil doesnt get below 32*, correct? So if I attach the temperature probe to the coil, I can monitor the coil temp and get an alert if it ever does get down below freezing? Or am I incorrect?

Hopefully that valve was the problem, but this monitoring solution wont hurt, and wont cost me anything but time. (and a zip tie LOL)

You are correct.

Evap Coil temp for most residential systems is 40 degrees.

IMO, anything below 35 under normal conditions is flirting with the danger zone.

Could be TXV. Could be airflow. Could be refrigerant charge. Could be a partially plugged drier. Intermittent problems are hard to solve sometimes.

The temp probe would need to be after the TXV but before the coil if possible. If it’s going to start frosting, it will start right after the TXV.

 

[Cameramonkey]

You are correct.

Evap Coil temp for most residential systems is 40 degrees.

IMO, anything below 35 under normal conditions is flirting with the danger zone.

Could be TXV. Could be airflow. Could be refrigerant charge. Could be a partially plugged drier. Intermittent problems are hard to solve sometimes.

The temp probe would need to be after the TXV but before the coil if possible. If it’s going to start frosting, it will start right after the TXV.

I was going to zip tie it “downwind” on the back side of the coils where the ice seems to start.

Thanks.

 

[ChristianPatriot]

I was going to zip tie it “downwind” on the back side of the coils where the ice seems to start.

Thanks.

My only concern with that would be getting a false reading from the air moving across it.

Keeping it out of the path of the air as much as possible will give a truer reading of what the coil temp is.

But realistically it may not make a huge difference. Heck just play around with the sensor location if you’re up for it. Not gonna hurt anything.

 

[DoggyDaddy]

Never had coil icing. I really like coconut pecan icing like on German chocolate cake. Cream cheese icing is good on carrot cake too.

 

[JCSR]

Has the defrost mode been checked?

 

[Cameramonkey]

Has the defrost mode been checked?

Defrost mode? Never heard of her.

Im talking about the indoor unit, not the outdoor unit if you are talking about how a heat pump reverses temporarily to . defrost the outdoor unit.

This is a straight AC unit only for a small-ish server room. So I dont think that applies.

 

[JCSR]

Defrost mode? Never heard of her.

Im talking about the indoor unit, not the outdoor unit if you are talking about how a heat pump reverses temporarily to . defrost the outdoor unit.

This is a straight AC unit only for a small-ish server room. So I dont think that applies.

 

[bigretic]

Had this happen a year or 2 ago on a server room split. Reality is that the spit was not spec'd originally for low ambient operation (commercial use year round... 40 degree low ambient cut off is very low imo, most of the stuff I've seen is more like 50 even though it seems to work) what is generally referred to as hot gas reheat on traditional stuff and even though it worked year round for 5 years or better it finally stopped. It would actually ice in or out and both, only a hard reset would get it working (after thaw) and after a while that didn't work anymore either. In the end we think it was a bad ecu/board on the cassette, but it gets to the point quickly that trouble shooting splits that operate erratically are not worth it. Wound up swapping it out for one with low ambient heater and actually wound up putting the spit inside the warehouse so it doesn't even matter. Have 3 of them running like that for "reasons" and it's honestly ideal for the equipment. In the scheme of 20 or 30k sq, the heat the put out doesn't matter. Back to the point, most hvac operations hate working on splits, they just want to change them. I've found it best to try and get support from the manufacturer and work with a service dealer that has a relationship with the manufacturer when necessary. We have at least 8 of those setups of different varieties. I mostly hate all of them. /end ramble...

 

[bcannon]

This is a straight AC unit only for a small-ish server room. So I dont think that applies.

Being a a/c unit only, is this unit a split system, with a separate condenser outside and a ducted airhandler(coilbox) inside or is it s self-contained wall pack(seen in most hotels), residential window unit?

 

[ChristianPatriot]

This is a straight AC unit only for a small-ish server room. So I dont think that applies.

Somehow I missed this.

Is this a traditional split system or a mini-split system?

Most mini-splits have low-ambient controls on them. Most traditional split systems do not. Being a server room I’m assuming it runs needs a/c pretty much year-round?

 

[Cameramonkey]

It’s a straight up air handler with an outdoor unit. They just don’t install a heat pack/exchanger.

 

[ChristianPatriot]

It’s a straight up air handler with an outdoor unit. They just don’t install a heat pack/exchanger.

The outdoor unit would benefit from a head-pressure fan cycling switch.