When could testing A/C units cause damage?

I am new here, and am ready for whatever hazing rituals I must go through on the forum to be excepted. My question is, what conditions, or weather conditions, could possibly cause equipment damage when testing A/C units?

I am asking because of my local inspection requirement verbiage that is as follows:
“Operate cooling systems when weather conditions or other circumstances may cause equipment damage”.

OK, Jorden, Here is a little hazing. Did you take the HVAC course? :smiley:


Haha, no…I’m on “New Mexico Home Inspection Standards of Practice” course, my first one lol. I am guessing the answer will be in that course? lol


Feel free to ask questions when needed. I was messing with you, have a good one. :smiley:

Standard answer.
Below 55 degrees, no cooling mode
Above 65 degrees, no heating mode

If the temps are between those two, you can test both. I run heat 1st, wait 30 minutes with the fan running and then cool next.

Many heat-pump manufacturers will also put similar information in their manuals. Go find one and read it. You will be surprised how many times you will look up manufacturer recommendations.


Thanks Scott, I get it. We might as well have fun on here. Anyways there is no point in waisting anybody’s time on this question if the answer in is in another course…unless Brian answers the question lol…thanks Brian.


Ummm all of my answers need to be cross checked, researched, verified and vetted prior to acceptance.

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You got that right, there is no sense in being a dry stick. :smiley:


Why not 50 or 60F? Where did 55 come from?

I always heard; “Don’t be a wet stick in the mud!”. LOL!

Different, in different areas, I guess. :grin:

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MY State SOP says no testing A/C under 65 degrees. I don’t honestly get it - why would the system be damaged at 60 degrees or even 55 degrees? Maybe someone could give a real answer to that. I have watched A?C technicians run systems when its way colder than that out.


Proper use of the english language is important when writing reports.
Examples in your posts: Excepted should be accepted
Waisted Should be wasted
For example. :laughing:



Haha, you know, I have never understood the english language… literally lol. Let the hazing begin lol.

And MY question is: "What homeowner (ever) has checked the outside temperature before heading over to the thermostat and ‘flipped the switch’?

Remember… answers beget more questions… if you’re paying attention!!

It’s about being able to understand why your doing something, instead of just doing as your told. It is the difference between a professional, and an expert in my opinion.

Also, if your confronted by clients as to why you did not check the a/c (that ended up not functioning properly the following season) you can give an actual reason.

I found the answer to my question on a technical level. I’m going to plagiarize from a thread on this website, from 2007. There are two different answers that support each other (I will provide the link)… As follows:

  1. " Under 65 degrees (an arbitrary number but with a good margin of safety), the refrigerant may not vaporize completely and you then have liquid refrigerant being sent to the compressor.

The compressor is designed for gas,which is more easily compressed than fluid. If you attempt to pump liquid through the system, you risk damaging the compressor. This can result in you writing a big check.

Since I HATE, paying my clients, (Much prefer they write checks to me!) I explain this to them when weather warrants and I report the AC was not inspected due to weather conditions."

  1. " The proper term is called (liquid migration) which occurs during the off cycle of the unit. Liquid freon will seek the coldest area of an enclosed system between the furnace A-coil and the outside condensing unit. When outside ambients are below 60 degrees the MFG recommends not to operate these units because the coldest area of the system will be the outside unit and if liquid freon is lying in the compressor you can can damage the valves in the compressor when you start it up.

Freon is simply stated, all about pressure temperature relationship if the home or the area of the furnace A-coil is in a warmer area than the condensing unit the freon will migrate toward the coldest area in a shut down mode. Once the compressor is actually started and operated in a normal mode no damage will occur to the compressore the damage will occur on the initial starting of the unit.

If the outside unit is equipped with a crankcase heater the possibility of liquid migration is almost nil as the heat will drive the liquid freon from the crankcase"


Prolonged low (cold) temperatures can cause an outdoor AC compressor oil to sludge. Ac compressor oil is carried by the refrigerant to lube the moving parts. Two things can happen when this occurs (sludging) and you operate the AC (compressor). First the compressor is not properly lubriccated and could seize. Second, gobs of sludged refrigerant can bend the reed valves in the compressor.

Note I said prolonged low temperatures. I also mentioned an outdoor compressor because some (notably heat pumps) are indoors (compressor). If you run a heat pump in the winter you are already running the compressor and it is not only safe to run the AC, it is necessary because you want to determine if the reversing valve works. Age and type of compressor will affect the severity or occurrence of the problems mentioned above.


From your answer, and the answer found from an old forum thread…looks like it can be called SLUDGING, or LIQUID MIGRATION.

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Just to add something else. I’m in Colorado and from one day to the next can be a 40+ degree difference. I had a client call me complaining that the AC unit did not work when they turned it on. I did this inspection 3 months prior this happening. I looked at the report and that day it was 31* in March. Now- in March this year we have had both multiple days of 70* then right after 18" of snow. That first part of your report that wants you to add the temp and outside conditions is not something to be ignored. That can save you 3 months down the road for all the above reasons of why you did not test the system.


Here is one source, Carrier heat-pump manual.