Thread: Running A/C in cold weather

Happy Holidays!
Quick question/Poll: I'm curious as to how many Inspectors run the A/C in the winter, yes colder than 65 degrees F outside. Those that do, is it because you were a HVAC technician and know which units can safely be ran? (I don't know a piston unit from another type, I'm thinking a lot of Inspectors are like me, and don't want to risk it. Heck, the unit could be bad to start with and if I run it outside of manufactures recommendations, my bad!)

I hate to tell customers I can't check an expensive system as the A/C unit, specially here in Arizona, it's life support! But, I don't want to buy them a new unit either!

Thanks guys and gals!

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Originally Posted by Dave Hill

Happy Holidays!
Quick question/Poll: I'm curious as to how many Inspectors run the A/C in the winter, yes colder than 65 degrees F outside. Those that do, is it because you were a HVAC technician and know which units can safely be ran? (I don't know a piston unit from another type, I'm thinking a lot of Inspectors are like me, and don't want to risk it. Heck, the unit could be bad to start with and if I run it outside of manufactures recommendations, my bad!)

I hate to tell customers I can't check an expensive system as the A/C unit, specially here in Arizona, it's life support! But, I don't want to buy them a new unit either!

Thanks guys and gals!

I do not
I also do not get on roofs that are covered with snow, ice, or frost.

There are some limitations that everyone must be willing to accept.

Originally Posted by Dave Hill

Happy Holidays!
Quick question/Poll: I'm curious as to how many Inspectors run the A/C in the winter, yes colder than 65 degrees F outside. Those that do, is it because you were a HVAC technician and know which units can safely be ran? (I don't know a piston unit from another type, I'm thinking a lot of Inspectors are like me, and don't want to risk it. Heck, the unit could be bad to start with and if I run it outside of manufactures recommendations, my bad!)

I hate to tell customers I can't check an expensive system as the A/C unit, specially here in Arizona, it's life support! But, I don't want to buy them a new unit either!

Thanks guys and gals!

I do, I find too many that do not work with high temps. I don't worry about it considering we almost never get below freezing, and it warms up during the day.
This AM inspection in A.J. I waited until the end of the inspection

Yes, within limits but I am one of those guys with an HVAC background so I am a little more risk tolerant. BUT, there are days when I will NOT start an a/c unit. There are limits to everything in life.

Heck my wife(hot flashes) has been running our AC whenever she gets hot no matter what the outside temps are for who knows how many years and our AC is still going strong! If anyone wants to tell my wife not to turn the AC on when she is hot my number is 302-1113, I wish you the best!

I do know that a Scroll compressor will tolerate running when it is cold better due to its auger design. Scrolls are tall and skinny compared to piston type that are short and fat...

Nope. My cutoff is 60 degrees. Anything below 60 is a no go for me.

Originally Posted by Jim Luttrall

Yes, within limits but I am one of those guys with an HVAC background so I am a little more risk tolerant. BUT, there are days when I will NOT start an a/c unit. There are limits to everything in life.

Ditto. I draw the line at mid 50's and shoot the outside unit with my thermometer. I have done inspections with an HVAC tech also doing an inspection who turned it on when it was pretty dang cold out. He said it wouldn't hurt it but also wouldn't tell him much, so really, what is the point?
If the client is there and is in the 70's or lower, I let them know that we are only going to find out if it runs, not whether it will cool properly when it is 90 out.

Good input. Thanks.

I agree with Scott P. I'm not an HVAC tech nor am I the smartest guy in the world....but I've stayed in Holiday Inn Expresses before.

I will generally run the AC last if I believe the temp will get close to 60, but I know for a fact that old units, new units and in-between units will run and blow cold air with outside temperatures less than 60

If the client seems overly concerned, I usually tell them to be sure and obtain a home warranty from a reputable company much like they would a home inspection. My mother in-law had a home inspection back in the 90's when she purchased her home, and the a/c worked fine at the time of inspection. The day after move in the unit quit running. Two days later, she had a brand new unit. On the flip side, I've had clients who have gotten thier warranty based on lowest price and were sorry they did. Just food for thaught.

Originally Posted by George Hallaron

If the client seems overly concerned, I usually tell them to be sure and obtain a home warranty from a reputable company much like they would a home inspection. My mother in-law had a home inspection back in the 90's when she purchased here home, and the a/c worked fine at the time of inspection. The day after move in the unit quit running. Two days later, she had a brand new unit. On the flip side, I've had clients who have gotten thier warranty based on lowest price and were sorry they did. Just food for thaught.

I know everyone here know this but just for the lurkers or people that stumble on this in years to come...The reason you do not run units below their design temperatures is the possibility to do damage to the compressor. Piston type compressors are designed to compress vapor, not liquid. When the compressor is colder than the evaporator coil, then the refrigerant will tend to pool at the compressor which is the coldest spot. When the compressor is started it sucks up the liquid and does bad things to valves, pistons, and rods.

Oh yeah, if you are standing next to one that slugs liquid you might needs a change of under garments.

Originally Posted by Jim Luttrall

I know everyone here know this but just for the lurkers or people that stumble on this in years to come...The reason you do not run units below their design temperatures is the possibility to do damage to the compressor. Piston type compressors are designed to compress vapor, not liquid. When the compressor is colder than the evaporator coil, then the refrigerant will tend to pool at the compressor which is the coldest spot. When the compressor is started it sucks up the liquid and does bad things to valves, pistons, and rods.

Oh yeah, if you are standing next to one that slugs liquid you might needs a change of under garments.

Jim,
I agree with all you have said, however, cold exterior temps will only damage a compressor if the system is over filled or does not have a high loop. When the compressor is stopped on a correctly charged and installed system there is little or no liquid refrigerant left in the evaporator coil. All of the liquid stays in the condenser coil which is also the coldest spot so no migration takes place. When I took my training in HVAC it was the middle of the winter and the classes were after dark. We ran six different a/c units every class without ever slugging once. As Scott pointed out with women in control of the thermostats of the world there would be no working a/c's after April 1st of any year if the 65 degree restriction held water. The problem comes from the ability of anyone surfing the net to read this impending doom to the compressor if run within 24 hrs of a less than 65 deg. temp. So if we test the unit, and it is already broken, we can be held liable. I don't like leaving out testing of such an expensive system, but I don't want to buy one for the seller either. I will test them but I have to have a good feeling about the system and circumstances before I do.

Originally Posted by Vern Heiler

...The problem comes from the ability of anyone surfing the net to read this impending doom to the compressor if run within 24 hrs of a less than 65 deg. temp. So if we test the unit, and it is already broken, we can be held liable. ...

Exactly

Also, running the A/C at below 60 deg will tell you very little about the condition of the system. It may seem to be working (blowing cold air) on a cold day but on a hot day it may not be cooling.

Originally Posted by Rick Cantrell

Exactly

Also, running the A/C at below 60 deg will tell you very little about the condition of the system. It may seem to be working (blowing cold air) on a cold day but on a hot day it may not be cooling.

Actually you can tell a great deal even on a cold day if you start with a warm house after running the furnace. You can tell if the compressor runs, if the condenser coils are blocked, that the outdoor fan runs, the thermostat works and even that it has a temperature drop. Granted you don't know the condenser will keep up on a hot day or if it is low on refrigerant.

Verrrrry interesting. I follow the guidelines of the largest electrical service provider around here, Excel, which won't run the A/C below 65 degrees. I tell folks that there are two things that we can't test this time of year....the A/C and the lawn sprinklers. I've only had one person call me up to complain about her untested A/C, but then I learned that she was complaining about her lender, her realtor, her title company, the cable company, the phon......well, she seemed to be a complainer. I had my HVAC guy call her, and she never called him or me back.

(e) The home inspector is not required to:

(1) Operate cooling systems when weather conditions or other circumstances may cause equipment damage;

From NC SOP as to when you should not operate AC equipment, can it be any more vague?

Alot of good comments, in cold weather climates you can run the A/C if the compressor has a crank case heater to keep the refrigerent boiled out of the compressor and then it will start with vapor and not try to pump liquid and hurt the valves on a Hermetic Compressor. Around here alot of the condensing units have thoses crank case heaters around the compressor and low ambient controls, like the heaters, head pressure control to cycle the fan to maintain head pressure. I guess you need to know what you are looking at and determind if it is ok to test the system. We test Heat Pumps in the cold and the only difference is the crank case heater, reversing valve and defrost cycle timer. Just use good judgment and if you think it is too cold, like below 55 then don't run it.

I have never seen a crankcase heater. Most of us can't tell if the system is overcharged. The high loop at the evaporator coil is only manufacturer recommended so it may not even be there. So I go by what Carrier states in their heat pump literature: "Do not operate unit in cooling mode when outdoor tempertures are below 55 degrees F unless your unit was modified for low-ambient operation." Again how can we tell if it has been "modified.

Also by Carrier: "Do not operate your unit in heating mode when outdoor temperatures are above 66 degrees F unless you set your thermostat to emergency heat mode."

Here is some more info from "AHRI: Fundamentals of HVAC/R" by Stanfield and Skaves. LOW AMBIENT CONTROL: The most common mechanical failures include liquid refrigerant floodback, liquid refrigerant slugging, oil slugging and flooded starts. If the liquid cannot leave the compressor quickly, the mechanical force is quickly converted into thoudands of pounds of hydraulic pressure and something will break. Operating an air-cooled condenser at low ambient tempertures can drastically reduce the system high side pressure. In winter, condensing pressures can drop 100 psi or more; thus the pressure across the expansion device may be insufficient to maintain control of liquid flow. Evaporaor operation becomes erratic. At outdoor temperatures of 65 degrees F and lower, systems with fixed restrictions and no head pressure control cannot operate reliably. Also: Most AC manufacturers recommend that refrigerant lines not be run underground. Lengths of underground lines create a large, cool trap to condense significant quantities of refrigerant on the off cycle. This refrigerant is then delivered to the compressor as a liquid slug on startup. (Each of the previous sentences were found in different pages and chapters)

Every now and then someone will complain that a question has already been asked and discussed "ad nauseum". I think any question is great, even re-curring ones, because there will always be someone out there with a new answer that no one has heard before or a new twist. Ask on!

Originally Posted by Frank Adame

I have never seen a crankcase heater. Most of us can't tell if the system is overcharged. The high loop at the evaporator coil is only manufacturer recommended so it may not even be there. So I go by what Carrier states in their heat pump literature: "Do not operate unit in cooling mode when outdoor tempertures are below 55 degrees F unless your unit was modified for low-ambient operation." Again how can we tell if it has been "modified.

Also by Carrier: "Do not operate your unit in heating mode when outdoor temperatures are above 66 degrees F unless you set your thermostat to emergency heat mode."

Here is some more info from "AHRI: Fundamentals of HVAC/R" by Stanfield and Skaves. LOW AMBIENT CONTROL: The most common mechanical failures include liquid refrigerant floodback, liquid refrigerant slugging, oil slugging and flooded starts. If the liquid cannot leave the compressor quickly, the mechanical force is quickly converted into thoudands of pounds of hydraulic pressure and something will break. Operating an air-cooled condenser at low ambient tempertures can drastically reduce the system high side pressure. In winter, condensing pressures can drop 100 psi or more; thus the pressure across the expansion device may be insufficient to maintain control of liquid flow. Evaporaor operation becomes erratic. At outdoor temperatures of 65 degrees F and lower, systems with fixed restrictions and no head pressure control cannot operate reliably. Also: Most AC manufacturers recommend that refrigerant lines not be run underground. Lengths of underground lines create a large, cool trap to condense significant quantities of refrigerant on the off cycle. This refrigerant is then delivered to the compressor as a liquid slug on startup. (Each of the previous sentences were found in different pages and chapters)

Every now and then someone will complain that a question has already been asked and discussed "ad nauseum". I think any question is great, even re-curring ones, because there will always be someone out there with a new answer that no one has heard before or a new twist. Ask on!

Nice post! I may cut and paste that into my comments for my engineer clients (seem to have alot of those lately).

Originally Posted by Frank Adame

Also by Carrier: "Do not operate your unit in heating mode when outdoor temperatures are above 66 degrees F unless you set your thermostat to emergency heat mode."
!

Didn't know that. Good thing that I rarely see heat pumps here, but good to know.

No I never run an A/C unit if it is colder than 60 degrees, but I do note it on my report that, due to cold outdoor temps did not operate the air conditioning system due to possible damage to the compressor when ran in cold weather. I then advice the buyer to have the air conditioning system checked and serviced by a professional when weather warms, some ask the realtor to include in contact with seller that in case the air conditioning unit is in need of repair the seller is responsilble for any repairs when weather warms and sevice can be made.

Quality Home & Building Inspection Consultants
Ken McConnell

Most literature I've read 55° is the cutoff for running your A/C unit. But what if the unit is on the north side of the house and it's really 45°? I would wait until about 2pm on a sunny day with the house warmed up to 75° when the outside temperatures are going to be that cool. One tip I would add is some new t-stat can be programed not to run when below a set house temperature. So you might think the unit is not working, but it's just because the house is not warm enough and the t-stat has been programmed not to run the Condenser.

Like somebody said you can see it run, but will it really cool the house come summer?

Vern is on the right track... there's a way to simulate higher temperatures so far as the condenser is concerned too and you will absolutely avoid damaging the unit

I'll let you go there if you want to Vern. It seems as if you would know this one.

Bottom line is that "Yes" you can run systems substantially below the 60 degree limit that some manufacturers impose.
But the bigger question is "Why" risk damaging a unit if you are not reasonably sure that it is not going to cause damage?

Yes, I can, and do. I just operated a package unit today with temps down into the 40's. But again, my choice because of knowledge. If you don't have comfort, don't operate systems when it is cold. It CAN cause Extensive damage.

Keep in mind that typical residential systems are designed to operate "normally" during anticipated working conditions. In short…when its hot outside. This means that the typical system will not likely behave "normally" when operating in a low outdoor ambient temperature condition.

Even if the system is not damaged at all during the low outdoor ambient operation, you still will not be able to ascertain much about how the system will later perform when its warmer outside. So here’s the real question; Why risk damaging the equipment when there is so little to be gained by turning it on in the first place during a low outdoor ambient temperature condition?

The ramifications associated with the above question is why so many inspection SoPs allow the inspector to opt out of operating the A/C system in cooling mode under low ambient conditions. Basically there is a recognition there that its probably not worth the risk and the inspector is let off the hook if he chooses not to turn the system on.

Now having said all that I will say that I am also an old HVAC guy like Jim Lutrall. Subsequently, my personal tolerance level for cranking on the A/C unit during cold weather is rather high as is his apparently. I do however take the individual system into consideration and even still opt to fall back on the SoP opt out from time to time.

Absolutely agree Phillip, I declined to operate a couple just a day or two ago. THERE IS A REASON that the SOP has a opt out clause, USE IT!

Here is an interesting variation on refrigerant floodback to the compressor:

"Some homeowners will close off the vent to rooms that are not in use or commonly used such as spare bedrooms. If enough of the system's capacity is shut down as a result of this attempt to economize, it can actually cause major problems with the system itself. For examle, reducing the airflow below the manufacturer's specifications can reduce the heat load on the evaporator. This can cause refrigerant floodback to the compressor, shortening its life. Another example is raising the discharge air temperature of a gas furnace by restricting the airflow through it. This causes the high limit to cycle the furnace off and on, reducing its efficiency. ln an attempt to economize in this manner may ulimately result in higher utility bills and shorter equipment life for the owner." (AHRI:Fundamentals of HVAC/R)

Dave,

Maybe your question should have been; I'm curious as to how many Inspectors run the A/C in the wintertime in Arizona?

Our temperatures here are slightly different than the rest of the country. When I was first starting out, I talked to a lot of home inspectors and Realtors to see what was normally done in the Phoenix area. Everyone I talked to claimed that the A/C was operated during the inspection in the winter months.

I guess it depends on how much risk you want to take. While I will not run the A/C first thing in the morning, I will run it at the very end of the inspection. Monday’s inspection I ran the unit at 11:00 A.M. for about 10 minutes to make sure it was working. While temperature splits will not tell you a whole lot, you can still get some meaningful information.

I once took a blue plastic tarp with me to an inspection and covered up the outdoor unit when I first got there. By the end of the inspection the temperature under the tarp was over 90 degrees. If we had a very unusual cold night I might be tempted to do the same thing again. However, so far I haven’t felt the need to do that.

Jeff Euriech
Arizona Prime Property Inspection LLC
Peoria, Arizona

Originally Posted by Frank Adame

Here is an interesting variation on refrigerant floodback to the compressor:

"Some homeowners will close off the vent to rooms that are not in use or commonly used such as spare bedrooms. If enough of the system's capacity is shut down as a result of this attempt to economize, it can actually cause major problems with the system itself. For examle, reducing the airflow below the manufacturer's specifications can reduce the heat load on the evaporator. This can cause refrigerant floodback to the compressor, shortening its life. Another example is raising the discharge air temperature of a gas furnace by restricting the airflow through it. This causes the high limit to cycle the furnace off and on, reducing its efficiency. ln an attempt to economize in this manner may ulimately result in higher utility bills and shorter equipment life for the owner." (AHRI:Fundamentals of HVAC/R)

I've often wondered about this with zoned systems where, suddenly, the 1000 sf master suite is using the full capacity of the 5 ton system.

I inspected a house with a 2006 Trane heat pump. The temp had dropped in the low 40's during the night and hit 57 by 11am. During my panel box looksie, I noticed the AC 30-amp breaker had tripped. When my client arrived at 11am, I showed him the breaker and explained there was something very wrong with the condenser. I couldn't be sure exactly what. He said go ahead and reset it. It did reset and held. Next the t-stat, next outside, next black billowing smoke from the condensing unit. I quickly turned off the disconnect. Now the real fun started.

The listing agent quickly found out, called me asking if the house was going to burn down and why did I test the AC during cold weather since "all" inspectors don't do that. I tried to explain that rule is not set in stone. She turned around, started walking away and muttered so I could hear "jerk!"
For the next 15 minutes I screamed my heart out within a foot from her face to defend myself. She threatened to call 911. At that point my client had to pull me away.

An AC tech that I called finally arrived and after some testing found out the compressor had locked. The agent let it slip that the owner had an ongoing problem with this unit. My client, to his credit, admitted he had requested for me to turn it on. He also said the AC had been on for the past week on previous views. The tech explained since the breaker had tripped before I got there. the problem was old. The burn out wasn't my fault.

Still, what a fiasco, with me nearly spitting on a realtor, and all because I decided to test the AC during cold weather. I will still test if I feel it's safe to do so. I'll just have to carry extra spit, just in case.

Frank
Thanks for sharing that with us.
I.m not faulting you, but I would like to use your story to emphasize to others what not to do.
#1 If a breaker is TRIPPED, do not reset it.
It tripper for a reason. Your job is not to determine why it tripped, just report what you find.

#2 Rarely if ever, should you operate the AC in cold weather.

#3 Someone will blame you for anything and everything bad that happens. That's just the way it is.

I too will use your story to illustrate what not to do.

First, just because a client asks you to do something doesn't mean you should do it. You're the one with the knowledge and expertise to know what you should and shouldn't do. Yesterday, I had a client get frustrated because I wouldn't turn on the AC at 20 degrees! Sometimes, even laboriously explaining something will not satisfy a client who has no knowledge of what you are talking about. You do your best to explain and then move on. He'll get over it and I already have.

Secondly and more importantly, never loose your cool like that. That is not only a loss of professionalism but also could cause problems for your client's deal and negotiations. (I know from first hand experience as I did the exact same thing once on a lying sack of garbage agent. I was completely in the right and totally wrong to go off on the piece of sh.........er......manure agent)

You are or should be the knowledgeable professional and must demonstrate that to retain your credibility. Just some very friendly advice from someone who has been there and done that.

I feel your pain, Frank.

As far as resetting breakers and turning on water valves that are off, I tell clients I will not do it because there may be a very good reason why these things are off and I will not take the risk or accept the liability.

I also tell the buyer and agent that if they will accept responsibility They can turn them on. Most of the time they do. I also make sure they turn off everything before we leave.

I will not let anybody run the AC in cold weather.