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Running AC in Winter


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Most of the time in multi-unit buildings the outside AC compressor units are all lined up and not marked as to what condo they go to. My client wanted to know which one was his so he ran it for about 2 seconds while I identified from outside.

I doubt this could cause any harm. Any thoughts on this?

My report did state that he operated this on his own against my advice.

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He could have IDed his unit, if this was so important to do, by manipulating the breaker and checking for power with a voltage sniffer, power is off to this one, now it's on.

The point being he hasn't bought it yet, not his to play with.

Not that you damaged it but why take a chance?

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Most of the time in multi-unit buildings the outside AC compressor units are all lined up and not marked as to what condo they go to. My client wanted to know which one was his so he ran it for about 2 seconds while I identified from outside.

I doubt this could cause any harm. Any thoughts on this?

My report did state that he operated this on his own against my advice.

Yes, it is possible to damage it but you likely would have heard it and hit the deck if it was slugging liquid. If you heard no unusual sounds then don't sweat it.

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While I continue to operate under the popular misconception that operating AC during winter damages it, it doesn't do any harm. There are several issues involved; is it a reciprocating type, scroll, are there crankcase heaters (usually), sensors to detect pressure inadequacies or other safety shutoffs, etc., etc.?

Disclaiming it due to weather doesn't elicit any complaint because it's CW here that one should never run an AC in temps <60-ish, and it knocks 20 minutes off the job. Due to CW, there's an army of tech's thrilled to condemn any unit operated in winter, and blame the HI, thereby selling a new unit. I sidestep the whole imbroglio. Win-win-win.

In the "old days", condensing/compressor units could be blown badly by operating them in cold temperatures, for several reasons someone else can describe. New scroll compressors don't have the same issues. Damn things are damn near bulletproof. Expect a chorus of experts to proclaim me sadly mistaken and a fool. Let me elaborate.....

Refrigerant be it liquid or vapor does not have to have a compressor operating for it to move in the system. Refrigerant always moves by itself to the coldest area of the system when the unit is off. The warmth of the indoor furnace will always drive the refrigerant outside to the condenser (liquid migration is the term). The refrigerant in some cases (depending on the amount of refrigerant and the size of the condenser) will back flow into the compressor and mix with the oil. This is the commonly accepted reason why we shouldn't do what Mike did.

When one starts the A/C in cool conditions, it will be pumping liquid refrigerant and the oil out of the compressor and when this occurs that is when the discharge valve in the compressor can be damaged. If the valves are not damaged the second possibility would be if all of the oil is pumped from the compressor; running an engine without oil....we know what happens. Same thing if the oil is too cold.

That being said, the new scroll compressors do not have the old standard discharge valve plates and these compressors do a pretty good job of pumping oil and liquid refrigerant without damaging the compressor. Damage could occur if all of the oil was pumped out and did not return promptly, but the odds of that happening are next to none.

I suspect AC techs, mfg's., or whoever is involved with the unit in question, like to promote the idea of damage, probably for the same reasons roofing mfg's. and installers like to promote the idea of roofing being damaged by walking on it or not ventilating it, or similar inanity. It's a way to limit liability...."you ran it in winter, you're out of warranty!".

**Some of the technical aspects I posted were cut from a Home Inspector Pro forum several years ago, then edited and generally forgotten. Attribution to the HIPro forum guy, whoever they are.

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He could have IDed his unit, if this was so important to do, by manipulating the breaker and checking for power with a voltage sniffer, power is off to this one, now it's on.

The point being he hasn't bought it yet, not his to play with.

Not that you damaged it but why take a chance?

It's very important to do. Mike and I work in the same environment; we go up on roofs where there might be 30 (or more) units of all ages and conditions. You want to know which one is yours.

Trying to check them in the manner you described is certainly possible, but not at all practical. It would take two people with 2 way radio contact, and access to electrical panels that may not be available, and even if they were, it would mean opening up dozens of disconnects and then having to rely on an unreliable voltage sniffer. Yes, one could get out the Wiggy, and add several minutes to the job. Feel free to quibble about how easy or not, regardless, it's a major PITA.

Even in summer, it's a problem. They're all running. Which one is the subject unit? It's a problem to figure out, and it can add a half hour or more to the job.

If I can't figure it out within a reasonable time frame, I've taken to putting it on the seller to tell me which one it is, and stating it in the report. Yeah, it's a punt, but I don't care. The seller has to take responsibility to tell us which one it is.

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While I continue to operate under the popular misconception that operating AC during winter damages it, it doesn't do any harm. Disclaiming it due to weather doesn't elicit any complaint because it's CW here that one should never run an AC in temps <60-ish, and it knocks 20 minutes off the job. Win-win.

In the "old days", condensing/compressor units could be blown badly by operating them in cold temperatures, for several reasons someone else can describe. New scroll compressors don't have the same issues. Damn things are damn near bulletproof. Expect a chorus of experts to proclaim me sadly mistaken and a fool.

I suspect AC techs, mfg's., or whoever is involved with the unit, like to promote the idea of damage, probably for the same reasons roofing mfg's. and installers like to promote the idea of roofing being damaged by walking on it or not ventilating it, or similar inanity. It's a way to limit liability...."you ran it in winter, you're out of warranty!".

It's a compressor, not a pump, so liquid will damage it. The older units had reed valves which is basically just a flapping flat piece of metal that shuts a discharge hole closed while the piston sucked in more gas through another port. Scroll units don't have any valves at all. Don't really need one because there's no piston. They draw in gas on one end and push it out the other end simultaneously. But it's still a compressor, not a pump so if you abuse it, you're risking damage.

Marc

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Marc, there's no useful value in your comment.

Carefully delineate and parse out each word and phrase, you will see why.

I'm up for useful information, not unsupported warnings about risk. I got plenty of risk scattered everywhere; don't need generalized admonitions against unlikely ones.

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I have been doing HVAC/R work since I was 10 years old I learned from my two uncles as a kid. I have been certified for 16 years! I am a American Standard Dealer "aka Trane"

I can tell you I have ran many units in 30*F weather when we are doing maintenance. I would not sweat it at all.

The issue with running a unit in the cold is if it runs to long with to low of a temp across the evaporator "The Cold Coil" you will not produce any superheat on the suction side of the system. If the refrigerant is not superheated that means it did not change from a liquid to a gas. This is real bad for older reciprocating compressors "Ie ones with pistons like a car engine" as the compressor cannot compress the liquid it will bust a reed valve or blow a hole in the piston.

When a residential HVAC is shut down the suction side fills with expanded gas that has passed through the expansion device until the pressure is the same on both suction and discharge sides. As long as the line set has at least a 24" vertical rise from the air handler before going down to the condenser you have no issues with oil flooding back.

So before you run the risk of flooding back the refrigerant to the compressor you must compress all the refrigerant subcool it in the condenser and pump it to the evaporator. By this time you have heard the unit run and shut it down.

Also some units have controls that make the unit stack unneeded refrigerant into the condenser to reduce refrigerant flooding.

If you need to run the unit for a longer time say it is only you at the location doing the inspection you can put the heater on and get the indoor temp up to 75*F to 80*F then shut the system down let the blower stage off and turn the AC on. This will give you enough time to go look at the unit and drink a cup of coffee before you need to shut it down. Remember its the air that is going across the evaporator we are concerned with!

Now if you have a scroll compressor you have even less to worry about, I have seen people connect residential A/C condensers to walk-in coolers that run all winter with no safety controls and never have an issue.

A scroll compressor works by having a dynamic scroll rotate inside a static scroll and does not use a piston so a small portion of liquid can be pushed through the compression stage. In fact some large scrolls have liquid injection in ordered to cool the scrolls down.

If the unit is a Heat Pump you can put the unit into heat pump mode and now the out door unit will produce cold air "it becomes the evaporator" and the indoor unit will produce hot air "it will become the condenser". A heat pump has an additional component called a refrigerant accumulator this device ensures that no liquid will get to the compressor to cause damage. Heat pumps are designed to run in 20*F weather and will run until the outdoor coil freezes up then go into defrost and turn on the auxiliary heat system "ie Electric, Gas, or Oil heat"

Sam

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Well my units have run many hours during the winter months with temps below 40f for about 7 years and I don't notice any issues with the units, they are scroll units. We have had a houseful of guest at various times and it gets warm and on goes the A/C to cool off the house. Not to mention my wife's estrogen driven hot flashes! I'm in the same ideology as Kurt when it comes to A/C units running in cold weather.

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Sam, thanks. That's a better explanation than mine. Mine is tailored to my customers.

No Prob, I am just moving into inspections and I have been poking around here for the past day or so. I will offer all the HVAC help I can as I learn inspection from you guys and gals.

Another way if you are just afraid to run the system is to turn the power off to the indoor unit. Open the thermostat and disconnect the Y wire "most of the time its yellow" and connect a Fox and Hound "this is just a toner that makes noise with a portable speaker" you can get it at lowes. put one clip on the yellow wire you disconnected and put the other on the C terminal "C stands for Cyan and a Blue wire Most of the time" then you can take you speaker and go out side and listen for the wailing sound on the small control wire going to the units.

Once you locate your unit hook every thing back up.

If it were me I would want to run the unit to ensure it is in operating condition. But to each his own I guess.

Sam

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