testing AC in winter?

I have heard that there is a way to test the AC in the winter without risking damage to the compressor. Has anyone heard of this or know how to do it? Thanks.

Not me Andy. I do not test them in the cold weather. It is different than a heat pump, but I’m not sure how it is different. sorry, not much help

When temps are below 60, I don’t test them and mark it in my report. However, I was on one of these free conference calls with Mike Crow and he briefly mentioned something about this and it sparked my interest.

Yes there is.

Are you EPA certified to handle ozone depleting agents?

You need to access the refrigerant circuits on the equipment to do this.

Wow. No, I’m certified in a number of things, but ozone depleting agents is not one of them. Sounds like for the average home inspector, the AC is off limits come winter time.

Never and most HVAC techs won’t do it either.

LOL i do have that one, mine was good international actually . i have had it in 1996 i think, ill have to find it

Someone please post this restriction of no test below 60 degrees from a manufacturer. A/C units run with outside temps below 60 all the time. This rule only relates to units with no power supply within the last 24 hours and temps below 60 degress within the last 24 hours.

I don’t but I always think of a family get together at thanksgiving with everyone in the kitchen cooking and someones says, “it’s hot, turn the air on”. Never heard anyone say, “wait! What’s the outside temperature?!” You would think there would be some kind of cautions in the owners operating manual but I haven’t seen one. Still I don’t test.

Besides Tim, we all live in the tropics in comparison to many!

For those that do “turn on”, what/how do you evaluate the test?

It is not that you can’t run them it is more that you are operating them outside the normal design parameters. Typically (if you use your head) there is no need for air conditioning if outdoor ambient is below 70. (78 by my personal comfort zone not taking into account Relative Humidity) and I personally won’t evaluate them as a Home Inspector below 75 F outdoor and a minimum of 75 F indoor because you need the indoor heat loads, the main reason we all have air conditioning.
Many air conditioners are equipped with factory installed low ambient controls to prevent operation in low temperatures while with others it is an advisable option.
So if the a/c doesn’t start are you going to determine that the low ambient control is stopping it or are you going to bypass this control to determine if the a/c is operating satisfactory? Or are you going to assume that it is not responding to the thermostat and recommend further evaluation? Or are you going to say it is operating ok based on what,delta T?
Yes air conditioners do run at temperatures below 60 with the proper accessories and depending on humidity they will utilize an economizer section for “free” cool air or the use of a head pressure controls to maintain reasonable operating pressures.
You are correct, the manufacturer does not say NOT to run below 60 BUT the references and tables given by the manufacturers to trouble shoot and diagnose is typically limited to a temperature range of 60 degrees F to 115 degrees F. Any adjustment of refrigerant outside this range is not recommended. Furthermore manufacturers recommend that operation below 60 F only with the use of appropriate accessories.
Now given that, even if you have a heat pump (which does run in low ambient) that requires a refrigerant adjustment, a tech may ESTIMATE an adjustment of the refrigerant charge based on temperatures, pressures, installation and operating characteristics of that particular unit BUT the corrected charge should be re evaluated under normal air conditioning operating conditions typically 85 to 115 outdoor air.
If you need residential air conditioning temperatures below 60 it’s called a walk in cooler, refrigerator or freezer. If you have an indoor load that requires air conditioning in a home when outdoor conditions are 60 or less open a window.

Note temperature ranges on tables below. I don;t think the tables stuck to this.

When an ac is installed, the outside temp needs to be above 65 degrees in order to calibrate it with the proper head pressure. maybe that has something to do with it.

Robert you give a perfect example, often times in my area the overnight temp could be below 60 and easily be in the 70-80 during the day. Steven I agree that a minimum temp is needed during installation. Now to Gordons post what if you decided not to test the unit because the outside temp ws 72 degrees, after closing the buyer finds the compressor is locked. What facts will you base the 75 degree min. temp on.
I would like for someone to post something from the manf. stating do not test below a certain temp.

An HVAC tech. told me that that the oil in the condensing unit cannot circulate properly when the outside temp is below 60 degrees.

that is what i have heard that the compressor may overheat becuase of the oil is not circulating or not there.

Yeah that was probably worded poorly. I do run them at 60 F and greater but I don’t evaluate the refrigerant charge per say in conditions less than 75 F. I only observe that the unit(s) responded satisfactory to operating controls. Such as compressors and associated fans and what I consider reasonable operating temperatures given the conditions.
Any reference to system charge or unsatisfactory cooling should be evaluated by an HVAC contractor under ideal conditions (because that is when the problem will be noticed not at 60F) as per manufacturer’s specs.
These operating characteristics are typically on the interior of the electric panel
and that’s where you will find the limitations to operating as per manufacturer.
I have never had any problems, my clients are reasonable and understand the limitations if explained properly.
Your best tools are touch, listen, look before you bring out any real tools. I have also observed many problems using this approach. You can hear a seized compressor trying to start or hear that it is not running or other abnormal sounds.
You can see frost or iced coils and compressors, you can see lack of condensation and you can feel temperature differences by hand if you know where.
Let the a/c run for 2 - 3 hours (under proper conditions) while you are there and you will also get a good idea if it is working within reason.

Refrigerant will migrate to the coldest part of an a/c, the outside section. Oil in the crankcase of the compressor will absorb the refrigerant as a liquid. When you start the compressor you reduce the pressure in the crankcase. When you reduce the pressure on liquid refrigerant it boils or evaporates. The rapid evaporation of refrigerant in the oil upon a cold start up will remove much of the oil from the cmpressor and it runs without the oil until it is returned. Oil circulates continuously in the entire refrigerant circuit not just the condensor.

Well ****! I learned something never posted here before!

Where is Ben?

Eldon, This is not a limitation set by manufacturer’s (to the best of my knowledge) But most inspecting standards state that the inspector is not required to test the AC unit below a certain temp. Our state standards, here it TX, state that the inspector should not operate when temps are below 60. I believe the NACHI standard states “below 65.” Following the standard limits liability. However, if there were a magic way to test them at lower temps, I’d like to know the method.


Section 20. About 2/3 of the way down. :wink: