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Posted: 6/15/2007 9:31:07 AM EST
[Last Edit: 6/18/2007 5:35:34 AM EST by OneMoreMonk]
MISSION: Residential A/C system, coil freezing up

BACKGROUND: Used A/C infrequently over the last few months, wife prefers fresh air and a fan until the humidity kicks up. Recent heat wave Tuesday night caused me to turn it on and leave it running. I noticed Wednesday that while the blower was going the air wasn't very cold, and the airflow was low.

STEP ONE: Changed the air filter. Hadn't been replaced since November and was pretty dusty. Airflow back to normal.
STEP TWO: Checked the feeder lines to the compressor. Frost/ice in various spots led me to the coil. Coil encased in ice.
STEP THREE: Shut it down, let the ice melt.
STEP FOUR: Checked and cleaned the compressor fins while the ice melted. I usually hose down the outside every month or so anyway
STEP FIVE: After an hour fired the system back up, frost on coil within 30 minutes.
STEP SIX: Shut down system, now I'm thinking low on freon.
STEP SEVEN: After verifying airflow isn't obstructed anywhere, blower fine, compressor fine, I call service company.
STEP EIGHT: Wednesday afternoon, service tech spends about an hour trying to recharge system. Finally calls main office which tells him to run the heat to be sure all ice/moisture out of coil.
STEP NINE: Run heat for 20 minutes. Run blower only for 20 minutes.
STEP TEN: Surprise! System now takes charge, only tech overfills system.
STEP ELEVEN: Tech bleeds system down...too far.
STEP TWELVE: Repeat running heat/blower.
STEP THIRTEEN: Tech fills system again (temping at about 38-40 degrees, "good" pressure according to tech)
STEP FOURTEEN: Tech leaves, system runs like a dream full time until this morning (Friday). 6:30 AM, frost on coil again, little cool air coming from system.

I've called the company and they're coming back out tomorrow. Thoughts? I'm renting, and the landlord is out-of-state. I prefer to solve problems myself. I'll ultimately get reimbursed, but I want the specific problem fixed.

My first thought was slow leak, but wouldn't that ultimately pull all the freon?
Could the tech have underfilled/overfilled and not caught it?
What should I be looking for when the "team" arrives?

I'm a pretty mellow guy, but I want the problem fixed...and only the problem.
Link Posted: 6/15/2007 10:34:03 AM EST
[Last Edit: 6/15/2007 10:35:16 AM EST by glk38]
make sure the teck hooks up both sides of the guages to make sure your pressures are not out of wack, so to speak ( high side and low side ).

Check your indoor blower squirl cage, if it's very dirty, there could be a lack of air flow there.

Could be any number of things concerning refrigerant or air flow.
Link Posted: 6/15/2007 11:32:46 AM EST
Tech team inbound for second pass, ETA 1 hour.

First tech had both sides on the gauges, even swapped to another set of gauges to double check his readings. Numbers went way up and way down as he made some mistakes. Final pressure was about 240 on one side, temp at 38+ when he left.

Squirrel cage is pristine, I use a shop vac to clean it out every six months (dust, cobwebs, a few bugs). Ducts are clean, too.

One added variable is that we have a freestanding dehumidifier running in the basement (stone foundation, 1940s tract house). It cycles on when the moisture level gets too high. I would think that would help the situation, though.
Link Posted: 6/15/2007 11:46:46 AM EST
The 38+ is no good, should be well above 60 on the low side ( 62- 63 is freezing), if he calls that good then he dosn't know what he's doing.

Sounds like it's a little more involved than just a refregerant thing.

Could have a restriction in the line set- expansion valve or acurator.
Link Posted: 6/15/2007 3:15:08 PM EST
2 hours later, still wrestling the issue.

System fully charged, no leaks. It's not a freon issue according to the tech and telephone backup. Pressure was 275 high and 65 low when we began. Temps been dropping, to about 33-34 degrees now. No change for 60 minutes. Compressor had a hard time starting, but runs strong now. Little bit of frost at the supply valves.

We're now comparing the temps at the inflow and the exhaust to see if there's more than an 18 degree swing.

Plenty of good return pull and all exhaust vents are open. We even removed the air filter temporarily.

No frost yet, and it's been running full tilt for two hours. But that's exactly how we left it last time.

Feel free to chime in, even the retired partner at this HVAC company is now in on the troubleshooting (by phone).
Link Posted: 6/15/2007 4:13:49 PM EST
Finally sent the tech home. System's running strong and we're going to see if it frosts again overnight.

Interestingly, pulling the filter brought the temp up to 36. After another hour it had settled at 34. Frost on the supply line to the compressor and on the high pressure line leading into the house. Some condensation on the line running to the coil.

Exhaust temp at the coil 49 degrees.
Inflow temp four feet before the fan, 74 degrees.

No filter may be the short term solution.

We both started wondering if the underside of the coil could be dirty. Might have to disassemble the vent around the coil to check it out. After staring at it for a long time I started wondering about mold or mildew buildup. Is there something that can be sprayed onto the coil that would clean it and drain off?

Any further feedback welcome.
Link Posted: 6/16/2007 3:42:06 AM EST
I missread the 38+ temp think, was looking at it as pressure, sorry.

They have coil cleaner made just for the sort of thing your asking about, and yes a dirty indoor coil can be just as bad as a dirty filer.
Link Posted: 6/16/2007 4:31:01 AM EST
This morning, after cooling the house quite nicely overnight, the coil has about 1/4 inch of ice on it and airflow has dropped significantly.

I've cut the system off to let it thaw, then plan to run the blower only for a while in hopes of melting any lingering ice. I'm off to the (BRAND NAME) DIY store in search of coil cleaner.

At least now I (and hopefully future ARFCOMMERS) know a lot more about my home A/C than I did when I started.

I'll post another update tonight.
Link Posted: 6/16/2007 4:31:38 PM EST
So far so good, nine hours later.

Coil cleaner isn't carried at Home Depot or Lowe's, I wound up getting it from the one HVAC supply company that has Saturday hours. $7.99 + tax and the stuff seemed to do the trick.

The system's been running full tilt and no hint of frost.

As I was cleaning copper, I hesitated on grabbing something like OxyClean or something similar at Target. If I wake up tomorrow and it's frosted over I'll post again, but hopefully this is the end of the story.
Link Posted: 6/16/2007 4:55:16 PM EST
Sounds like you got a hack company for your repair.

Frosting coils mean one of four things:

1) Plugged filter

2) Low freon charge

3) Obstruction in the freon pipes

4) Lack of air flow (blower/duct work/evap coil plugged)

A good tech should have had it diagnosed in 1hr or less and not needed phone calls from the office.

Now your system will be overcharged. Most hack techs will add freon to make up for the low pressures caused by a plugged evap coil. Now that you have the proper* airflow, you will have high head pressure.

* If a evap coil is plugged to the point of freezing you will need more than the self rinsing cleaner in a can to clean it. Turn the power off to the furnace and take a garden hose and blow the coil out. Let the furnace dry for 24hrs and you will be good to go.
Link Posted: 6/17/2007 5:51:19 AM EST
Checked it at 2:00 AM Sunday, thick layer of frost. This is getting tedious. Shut the whole system down.

Per advice above, I cut power to the system at the breaker.

Just finished hooking up a hose and blasting the hell out of the coil. Water was cloudy at first but turned clear after a few minutes of washing.

ZW17: Looking at your checklist I have
1. No filter at all at the moment.
2. Freon pressure high side 270, low side 60-65 (I read the gauges myself about ten times). High side came down to about 230 after running for two hours Friday.
3. Freon's moving (I asked about blockages to every single person), and we sniffed the whole system for leaks. I even took the sniffer myself and walked the length of the freon flow (coils, compressor, everything).
4. Blowers fine, duct work fine.

Strangely, the problem seems to only appear overnight after the house has been temping down. I had the thermostat at 74. Temp at thermostat was 75 when I checked at 2:00 AM.

Previous frosting episode was middle of the night as well.

Will wait the 24 hours for the system to dry out, fire it up and post an update.

One final thought. This system has an "A" shaped coil. Through an access vent I was able to easily blast both sides of the "A" but not underneath where it rests in the tray. Is that relevant? Water coming off the coil is clean now, and the tray and drain are clean and clear.

Additional feedback welcomed, thanks for the tips so far.
Link Posted: 6/17/2007 9:29:50 AM EST
Does the indoor A-coil have an expansion valve on it or a cap tube system? That is what regulates the refrigerant flow in the evaporator coil. What brand is it?
Link Posted: 6/17/2007 10:32:40 AM EST
Can't see the brand of coil without cutting the seals around it and disassembling most of the vents. Attached photos show what I can see of the coil.

Link Posted: 6/17/2007 11:44:47 AM EST
right off hand I'd say it was a cap tube system, need to see the other side to tell. What brand is the outdoor unit?

Could have some sort of restriction in the metering device, kinda hard to tell with out being right there. Like fixing them on the phone so to speak.

You might want to call another company besides the one that has been working on it or send sombody thats not fresh out of high school from the original company.
Link Posted: 6/17/2007 12:39:27 PM EST
25 degree difference = insufficient airflow.

are all your register's open?

are you sure the ducts arent crushed or blocked?

58lbs is the pressure that corresponds to a boiling or saturation temperature of 32 degrees F. at night, when the head pressure (high pressure, that 230-240 one, red guage normally) drops, the vapor pressure, if its at only 60-65 during the day, will drop below that 58lbs. and once the freezing process sets in, it's all over. the frost further impedes the airflow, making it freeze faster, and faster, til there's NO airflow thru the coil.

check ALL of your registers. hell, pull em out if they're all open, and reach back as far as you can with a flashlight, if possible. you could have flex ducting in the return that's collapsed, usually due to running it with an impacted filter. basically pulls a vacuum on the inner membrane, you may not be able to tell from just looking at the outside of the duct.

pm me the make and model numbers of the airhandler, and the condenser. what kind/size of house. i'll get you situated.
Link Posted: 6/17/2007 12:46:00 PM EST
ooph, 65# vapor, with zero superheat.... probably overcharged, now, too. most idiot technicians don't understand the significance of airflow, and it's impact on charge balancing.

where the two copper lines enter the coil, the smaller line (liquid) changes shape, could you get a picture of that?

if that 25F deltaT was due to ice restricting airflow, i.e. it hadn't thawed all the way, and the ductwork checks out fine, you have a) a crimped copper pipe or b) an obstruction at the metering device (orifice, TXV, etc)

and get a filter in that thing, yesterday....
Link Posted: 6/17/2007 12:52:37 PM EST
[Last Edit: 6/17/2007 12:58:12 PM EST by cmjohnson]
You want the evaporator coil to be running at 40 degrees. If it's in the 60s you won't get shit for cooling.

32 degrees is freezing. A 40 degree coil gives optimal cooling capacity without freezing up.

If the system is adquately charged and still is icing the evaporator coil, the most probable
cause is a bad metering device. Metering devices don't really go bad but they can get
obstructed by a foreign object in the system. A restricted receiver/dryer is also a
possibility, but if that's it, it's bad news as it takes more to clog one of those than
it does a metering device. Although, the receiver/dryer acts as the system's filter
and it's SUPPOSED to keep crap out of the metering device.

And that can be a bad thing. What can get into a sealed system and clog the metering

The answer is usually "Nothing you really want to hear about!"

It is often an indication of a compressor failure of some sort, anything from bits of metal
from a worn-out compressor assembly to a piece of reed valve that snapped off due to
metal fatigue or wear, to contamination in the system consisting of burned bits of
motor insulation...in which case you'd probably find a HOT compressor housing and
very flaky system operation if it worked at all.

I spent 2 years in college learning this shit. Anyone who thinks a 60 degree coil is
about right needs to stop posting about things he has no training on.

If the system frosts up again, get a photo showing exactly where the frost starts and
stops, while the system is running and just BEGINNING to frost up. The location of
the frost can be a valuable diagnostic indicator. A frosted receiver/dryer indicates
the restriction is there, and it's acting like a metering device. A frosted metering
device suggests that the problem lies there...or is a symptom of other problems as
I already mentioned.

Link Posted: 6/17/2007 1:52:05 PM EST
Damn cm johnson , lighten up, he is only asking a question on the internet
Link Posted: 6/17/2007 2:53:39 PM EST
Here's more images for your viewing pleasure:
The outside setup:

The compressor description:

The outside valves:

An overhead shot looking down at the coil:

Another overhead shot:

Yet another overhead shot:

Looking into the airhandler from the intake, filter sits about where the camera is being held:

One of three returns, straight shot down the center line of the house to the unit for two, one in back. All the same size. Pistol's for scale, and because this is ARFCOM...

Still drying everything out inside after this morning's wash, probably be another couple of hours.

To clarify all reponses since last post:
GLK38: see attached photo with compressor info on it

briansmech: return ducts are metal, all large rectangular style. No obstructions or internals to collapse. exhaust ducts are a mix of rectangular style with circular tin extensions at some ends, addition on rear of house is partially fed by one single line of insulated flexible plastic circular duct. (t splits into back room and back hall). notably, no return venting in back of house. no markings on airhandler, seems to be generic and/or label is long gone. House is single story craftsman style home, roughly 1500 sq ft?

cmjohnson: evap coil temp was 34-36 after the recharge and 2 hours of operation, 60-65 was low side pressure reading at same point, 230 was high side pressure reading - all this from the tech's gauge set. I'll fire the system backup in a few hours and see if its frosting outside at the compressor. Compressor fan and outside coils clean.
Link Posted: 6/17/2007 2:59:01 PM EST
as posted "if that 25F deltaT was due to ice restricting airflow, i.e. it hadn't thawed all the way"

The 25 degree differential was measure with a standard ambient thermometer, first resting on the coil then hanging in the return air duct. All the ice was thawed and gone, I even ran the heat to make sure. I'll do another set of temp readings after it's been running for a few hours tonight.
Link Posted: 6/17/2007 3:06:34 PM EST
cap tube system, I'd have them look into some sort of restriction in that, not sure what else to tell you

Has nothing to do with the outdoor part.

3 ton Goodman
Link Posted: 6/17/2007 3:26:07 PM EST
New wrinkle. Just fired it up to see where we were.

Compressor, outside fan started fine. Inside vertical air handler squealed like a pig, vomited water from my morning wash. Wife cut it off after about 20 seconds while I was on my way back inside. It's now dripping out, and down around the motor.

System's off, power cut. Portable fan is blowing through air handler to dry it further. I'm now thinking the air handler's going to have to come out and get some TLC, maybe some WD40?.

Please tell me I haven't ruined the air handler by cleaning the coil.

Link Posted: 6/17/2007 3:37:22 PM EST
[Last Edit: 6/17/2007 3:41:08 PM EST by cmjohnson]
Probably not. Look around the frame of the air handler motor for oiling holes, which are usually going to have a plastic cap on them, and the cap is usually yellow. If you find them,
put a few drops of light machine oil in them. That might take care of the squeal.

I don't SEE such oiler holes in the motor frame from the above picture, but that doesn't
mean they're not there.

Check the drain holes for the handler, too. Water should leave the air handler pretty quickly if they're not clogged.

Your coil temps are definitely a little bit low. Not much, but enough to start some frosting
issues, and once frost forms, it acts as an insulator, reducing heat transfer, and making
the problem worse.

Also, the system's covers DO make a considerable difference in performance.
Charging and testing should be done with the covers on as much as is possible.

Link Posted: 6/17/2007 3:38:27 PM EST
Reversing valve.
Link Posted: 6/17/2007 3:44:57 PM EST
let it dry out out. indoor blower housing is holding water from the hose down.

I would not have done that but you can remove the blower assembly pretty easily and dump the water out of it.

I know it's a pain in the ass but if you look at it you will see what I'm talking about.

If you vacume it out on a regular basis you may be able to shop vac out the water. good luck
Link Posted: 6/17/2007 3:46:47 PM EST
If it's a heat pump....maybe. IS it a heat pump? I haven't seen anything to confirm that in those photos.

Seeing where the frost starts is the single best piece of info we could get right now.

Link Posted: 6/17/2007 4:03:07 PM EST
Another update, more upbeat.

There were three holes on the side of the air handler, just above each bracket centering the motor. I gave each a shot of WD-40, and immediately fired the system back up. It's like Iraq, at this point...why not?

After a few seconds of balancing, the air handler is purring like a kitten. A few drops of water came out, but nothing major like I had before. Overall airflow is stronger than it was before, and the inside system is running much quieter than before.

Airflow at the coil is MUCH stronger. Access vent hole now blasts cold air in your face. Temps dropping all over the house in just a matter of minutes. I'll be monitoring inside and out for frost for the next few hours.

I started thinking that all these little pieces add up:
Dirty air filter
Low freon
Dirty coil
Dirty air handler
Unlubricated air handler

I will say this to all those that offered wisdom thus far...ARFCOM never ceases to entertain and enlighten. Thanks.
Link Posted: 6/17/2007 4:12:52 PM EST
That sort of thing does add up, try and stay cool
Link Posted: 6/17/2007 4:14:27 PM EST
WD40 will NOT work as a lubricant for very long. A few drops of light machine oil will be necessary. Ideally the motor should be oiled twice a year.

It's good that your problems were low-cost to handle.


Link Posted: 6/17/2007 4:36:39 PM EST
I have read up about the blower motor maybe not being lubricated. It's a sealed bearing motor so it won't need lubrication. I have run into motors (sealed) that become so dirty that they will only run 3/4 speed. The dirt in the bearings will cause them to seize up, partly.

If you can take a amp reading of the motor and see on the tag on the motor and compare.

I would still pull the center panel in the "A" coil and check for dirt build up on the inside. It can be bad and needs cleaning. It could also be bad enough to cause the motor to overheat due to over working and the motor will trip on thermal limit. Then the evap coil will ice like crazy.
Link Posted: 6/17/2007 5:14:46 PM EST
Blocked out the serial number. Love it!

Link Posted: 6/17/2007 5:49:31 PM EST
I hoped somebody would catch the serial number trick.

Two hours later, house is temping down nicely. Some condensation on outside lines leading to compressor, and spots of condensation on the high pressure line leading to the coil. No frost yet anywhere...

The WD-40 got blasted onto the air handler blade assembly. It had been producing a high pitched whine this season, now it's freaky quiet. All you hear now is the hum of the motor and the airflow. Airflow is stone cold and roaring.

Temps dropping much more quickly than before. Temp at thermostat was 83 when I fired it up about two hours ago. It's already at 77 heading for 74.

Link Posted: 6/17/2007 5:51:58 PM EST
this is the exact problem we had in our office, the damn AC tech told it was frozen and unplugged it for a day and then came back and it worked of course
Link Posted: 6/18/2007 5:34:25 AM EST
[Last Edit: 6/18/2007 5:41:25 AM EST by OneMoreMonk]
Final postgame report this AM. The only frost is on the beer mug I'll be using this afternoon.

System runs fine now. Aside from a bit of condensation where expected, everything checks out. I didn't test the airflow temperature differential, but based on the overall increase in efficiency (speed in cooling) and increased force of the airflow at the coil, returns, and exhaust points I'd say the correct diagnosis at this point was...

Airflow issue.

This was a useful exercise, because even though I had a very specific issue it was likely caused by an aggregate of factors I mentioned earlier:

Dirty filter (reduces volume of air to the air handler making it work harder for less output)
Low freon (reduces efficiency of cooling, increases likelihood of frosting, can strain compressor)
Dirty coil (this is where all the "conditioning" in air conditioning takes place, but I don't think a lot of homeowners understand how key this component is. When it is dirty, the total surface area of the coil for cooling is reduced. It's easier for the system to overcool and frost. Once it starts to frost it cycles upon itself until the frost builds to a layer of ice. At that point, the system is as efficient as blowing on an ice cube.)
Dirty air handler (the unintended side effect of blasting the coil with a garden hose was that I drenched the air handler. Lots of grey water came out, which told me that dust and other particulate was coating the fan blades of the handler. That also reduces efficiency, slowing the blades and making the motor work harder.)
Unlubricated air handler (this was the lucky discovery, the total shot in the dark. The motor is sealed, but the fan assembly or turbine is a spinning machine. Dust and grime buildup can definitely slow things down. The squealing sound told me there was little or no oil. A little WD-40 evenly applied, and after a minute or so to get going the lubrication distributed, it quieted the system down and let it return to full power.)

For anyone chasing a similar A/C crisis this summer I'd suggest the following mindset:

Does it work? The system did cool for short periods of time, longer in the overnight hours. No part was not functioning at all, as it turned out some were just underperforming.

Is is clean? As I discovered, there are several major components that require regular cleaning. A hour or two with a shop vac and a garden hose is good preventive maintenance spring and fall.

If it does need a freon recharge, is there a leak? I didn't take the tech's basic test of the compressor and coil for the definitive answer. While we waited, I took the freon sniffer and walked every inch of the copper.

When was the system last serviced? When I finally heard from my landlord today, it turns out the last time this system was serviced was February 2004, and that service was on the furnace not the A/C. She bought the house in fall 2003. Who knows when it was last looked at.

It took a lot of time to sort all this out, but in the end I was only out less than $200.00, and I'll get reimbursed. I could easily have let the landlord pay for it all, even if someone wanted to put in a whole new system. I looked at it like this though, what if it were my money? What if a friend or relative was having the same problems? I learned a lot, and now I can pass that knowledge on to you.

FWIW anyway. I could be back...Live Free Or Die Hard.
Link Posted: 6/18/2007 5:47:47 AM EST

Originally Posted By OneMoreMonk:
I hoped somebody would catch the serial number trick.

Two hours later, house is temping down nicely. Some condensation on outside lines leading to compressor, and spots of condensation on the high pressure line leading to the coil. No frost yet anywhere...

The WD-40 got blasted onto the air handler blade assembly. It had been producing a high pitched whine this season, now it's freaky quiet. All you hear now is the hum of the motor and the airflow. Airflow is stone cold and roaring.

Temps dropping much more quickly than before. Temp at thermostat was 83 when I fired it up about two hours ago. It's already at 77 heading for 74.


WD-40 is not a lubricant. It will wear out after a few days, as folks have said go find some light oil and use that. (not to say that the wd-40 wasn't a good idea, it's probably the perfect first step for you, but you do need something else for longer term use)
Link Posted: 6/18/2007 6:14:54 AM EST
Copy that on all the suggestions for using machine oil. I already planned on picking some up this morning, and plan to oil the outside fan while I'm at it.

Thanks again for all the feedback.
Link Posted: 6/18/2007 12:15:31 PM EST
"It's a sealed bearing motor so it won't need lubrication."

No, it needs it but you usually cannot get it into the bearings.
Sealed bearings are 'lubricated for life'.
The life is the life of the bearing.
When the lubricant is gone/contaminated the bearings life is over.
It saves a few pennies on having to supply oil ports that most folks will never use anyway.
Link Posted: 6/18/2007 1:36:09 PM EST
I agree, hard to find a motor that can be oiled and they don't build them like they used to.
Link Posted: 6/18/2007 3:34:32 PM EST
In some cases, you can drill an oiler hole into the motor at the bearing locations and then
you can oil it as needed and keep it running a lot longer.

Caution is advised here.

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