I will also add as long as it’s a normal room temp, ie not below the mid to lower 60’s
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R-22, next year will be this A/C’s last.
So you are indicating that the cooling capacity of the A-Coil isn’t being properly coupled to the heat source (my house in this case). So there is a surplus of cooling in the A-Coil, which becomes obvious when the humidity rises, and water can freeze on the A-Coil.
This baby is old, dirt in the fins is very possible. What is the best way to clean dirty aluminum fins? Yes, I have a compressor and air nozzle close by, is there a better, more effective way?
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I’m not an A/C guy but am here to say that low refrigerant WILL cause evaporator coils to freeze up. I had a super slow refrigerant leak in one of my units and my most reliable indicator that it needed a charge was that it would begin to freeze up. Coils were clean, blower and ducting fine. Thaw and charge and it would be good to go for another 4-5 months.
The reason low refrigerant can cause the coils to freeze is that low system pressure allows too much expansion of the Freon and a corresponding drop in temperature at the coil.
That said, it could very well be a dirty evaporator. Locke Supply sells coil cleaner in a spray can. It’s stuff you spray on and let sit - I don’t remember if you rinse it off or just let it drip off.
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Typically low refrigerant will cause cause it to freeze in localized areas of where the the refrigerant is distributed via cap tube or other metering device. Because it’s below freezing (58 Psig) it freezes, but because it is low on refrigerant the superheat is greater, The coil temp is then higher. Comfort cooling runs about 10-12 degrees of superheat. A comfort cooling is designed to be about 40 degrees with 55 degree supply air. Freezing of the full coil is rare.
In refrigeration, depending on the temp, runs colder depending on the operation temp. Refrigeration also normally involves colder temps that will freeze the coils under normal conditions, thus a defrost timer or other device to defrost the coil.
Russell, you can use a rinse free coil cleaner to clean the coil.I personally dont use the rinse free. I use the rinse required & use a shop vac or little enough water to keep from overflowing.
How wet does the outside coil get when it rains?? the wet coil lowers condenser pressure which lowers evap. pressure/temperature. Once a coil starts to freeze it restricts airflow enough to lower coil temp and make more ice. A fan cycle switch or maybe a gutter is in order.
Have seen this due to my hilariously bad “office AC boosting” arrangement some five plus years ago that resulted in backpressure on the cooling coils. It took about an hour every time.
Nah…the HVAC guys are stocking up on virgin R-22 and demand was lower than projected this year. They’ll be recycling R-22 still, so reclaim will still be available. If you have a slow leak it’ll be a pain, but do-able. I can tell demand is low because wholesale jug’s prices are down.
What’s R22 going for these days (wholesale)?
@mdredmond - look it up on the web. I would never discuss someone’s wholesale cost…that’s like asking someone for pics of their significant other naked…ridiculous and RUDE. If you want wholesale get your EPA certification, gauges, and order a jug online.
“Discuss someone’s wholesale cost”
I’m not discussing “someone’s” wholesale cost. Knock it off with the “RUDE”.
You referred to the “HVAC guys”, implying that they were some group other than yourself.
I AM section 609 certified (mobile) and was curious about ballpark numbers.
Finally, no, asking about Freon prices is NOTHING like asking for nude pictures of someone’s wife. That you would downplay the seriousness of asking for such a thing by comparing it to asking about Freon prices is a bit disturbing.
TBJK, helped me on a prior thread without demanding that I get my AC certification. I thank you for your kind and detailed help. That’s what makerspace is about. We are all adults with judgement enough to venture just a bit outside our areas of competence in DIY mode. After watching numerous youtubes and reading, the net effect is that I have even more respect for the expertise and cumulative knowledge needed for proper and timely HVAC maintenance. And I’ll be able to help my HVAC guy by having a bit of knowledge. All this aside, my post here is to vent my frustration and to show how I’ve neglected my system 
My home was remodeled some 20 years ago and I’m pretty sure they installed both air handlers before the added the 1/2 story. Thus one unit’s evaporator is practically inaccessible and this one is nearly so. 
We all have stories of “builder’s specials” as I’ve come to refer to these modes of construction. The other one in this house was the extra large water heater that was framed into it’s closet. (“Hmmm this won’t be a problem for about 15 years”) But this was surpassed by a friend whose second water heater was entirely framed and dry walled into its own space. Posed a bit of a diagnostic problem when it quit working.
My evap coil is at the end of a long attic crawl so small that it can only be backwards crawled to get out. Not fun for a 6’3" inflexible guy speeding toward old age. Sure makes you think about every tool you might need when you make that crawl.
Well, a minor builder special was discovered and in my entangled contortion I could not solve this puzzle. This evap cover was apparently installed prior to the drip pan and all of its plumbing (freon and drain). It simply was not removable. Nothing like a bigger hammer to do the job, or in this case a cutoff wheel or two or three to modify the cover. Thankfully there is a screw on the corner I had to cut off.
This revealed an iced coil. Yep, that would 'splain the lousy airflow and poor delta T at the vents. I’m letting it melt now. There is some possibility (my guess) that a dirty filter precipitated the initial icing and that the now clean filter and yet-to-be-cleaned coil will remedy the situation without other intervention.
I tried earlier and even had my HVAC guy (was a wonderful guy but sadly, passed away) try to clear the line. He used a CO2 blast but could not clear it. And he said part of his flusher assembly shot off and went down the line, further complicating the clog. But I’m committed to solving this problem before this disaster waiting to happen when the backup line clogs or the pan rusts through.
I guess I’ll reevaluate the coil after the ice melt. Likely to be a horror as it clearly had never been inspected as the cover required cutting.
So my plan:
- Inspect coil (flat type) and clean as possible.
- Replumb the primary drain, bypassing as much of the old one as possible since I don’t know the location of the clog.
- Measure suction and liquid line temps and pressures at the compressor after cleaning the system.
Any thoughts are welcome.
Cheers . . . DJ
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OK, the thing has defrosted. I thought I might be able to see either side of the coil, but it cannot be visualized in any way with the side panel removed.
Does one have to tear apart the ductwork to visualize the coil surface?
Looks that way. Does one tear off the silver tape? Not any room for me up there not to mention lack of space for moving that big duct. leading to the receiving side of the coil.
I could just go on in ignorance about the condition of my coil but I bet its a mess. Pretty sure it’s never been cleaned in 20 years.
BTW, my evaps are made for the old Freon but I had 410a compressors installed about 6 years ago and was told the old evaps would work and generally they have.
OK, got some cool results! And different on two units worthy of discussion. Dang, crawlin’ thru hot attics - need to rehydrate. I’ll post some numbers later.
Why don’t we have a few sensors throughout the system for self diagnosis?? There is obviously an art to some of the more subtle problems but one could record
- suction pressure at compressor
- suction temp at compressor
- suction temp at evaporator
- liquid temp at compressor
- liquid pressure at compressor
- liquid temp at evaporator
- ambient outside temp
- condensor exhaust temp
- return air temp
- return air flow
- air temp post evaporator in the air handler
Graphics over time could show various problems from leaks to bad compressors to faulty blowers, clogged evaporators, faulty txv.
Certainly a makerspace kind of project but so easy to build in and put on an R-pi for remote access.
I think those sensors would cost as much as a new evaporator. I would love to be wrong but the 800psi transducers I’ve found are not cheap. I would be happy to just monitor the superheat at my condenser.
Good point. I have not priced those.
Is this right?
Superheat is suction pressure–>look up the vapor temp on the gauge minus the measured suction line temp.
Subcooling is these respective measurements on the liquid line?
Yes. Exactly. Although, I just realized I have txv metering and my manufacturer recommends using subcooling. So I’d be happy to monitor my liquid line pressure and temp.
I have a txv on my units as well. I think that is mostly standard from what I’m seeing.
I’d say Flowrater & cap tubes are still probably more common, Followed by TXV. EEV or EXV are the next thing
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I’d love to look at the intake side of my evaporator coil. Do you have any tips on doing this with a horizontal flow system? Looks like I will have to remove some screws and silver tape on the ductwork from the blower to the evaporator and take down the side panel. Sound right?
