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Old 2/12/10, 12:32 PM
Frank Magdefrau's Avatar
Frank Magdefrau Frank Magdefrau is offline
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Join Date: Nov 2003
Location: Hernando, MS
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Default A/C units

Why do you not operate central a/c units when the temperature is below 65 degrees outside? Also will they even come on when it is 32 degrees outside?


Frank Magdefrau
Certified Master Inspector
DeSoto Home Inspection Services, LLC
3152 Big Ben S
Hernando, MS 38632
(901) 486-0421

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Old 2/12/10, 5:38 PM
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hmcclard hmcclard is offline
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Location: Raymond, NH
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Default Re: A/C units

Theoretically, one could test air conditioner at any temperature below 65, BUT, one would have to have sufficient test equipment and knowledge of thermodynamics (Bernoulli's Equation etc) to properly test due to the temperature being below the heat exchanger design limits and things like that; I really don't think we want to get into that though. Other than that, it's just a guideline I guess.

Harry "Bud" McClard
Serving All of New Hampshire
NH License 00024
National Weather Service SKYWARN certified
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Old 2/13/10, 7:44 PM
Bruce A. King's Avatar
Bruce A. King Bruce A. King is offline
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Location: Mt Pleasant SC
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Default Re: A/C units

Originally Posted by fmagdefrau View Post
Why do you not operate central a/c units when the temperature is below 65 degrees outside? Also will they even come on when it is 32 degrees outside?


Some will not come on, my 2001 model Bryant/Carrier heat pump units have outdoor sensors that disable the cooling mode when 55 or less.

I ran three units on a foreclosed house yesterday in cold weather for a few minutes just to make sure the refrigerant levels were not zero and that the contactor, fan and compressor would at least come on. If all of the refrigerant has leaked out a sensor will keep the compressor off. My client said he would rather know at least something about the three A/C units than zilch.

I had a client once that is a professional HVAC inspector, guess what he did in really cold weather? Yep, he turned on the A/C system for a minute just to see what it would do. I just wish he had not done it while I was standing over the unit checking the inside of the disconnect box....

B.A. King Home Inspections, LLC
Serving Charlotte NC area and Fort Mill SC areas.
CMI Certified Master Inspector and Independent
License NC2449 and SC1597

"Discovery consists in seeing what everyone else has seen and thinking what no one else has thought."
- Albert Szent-Gyvrgyi, Nobel Prize for Medicine 1937
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Old 2/21/10, 5:51 PM
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David Moriconi, CMI David Moriconi, CMI is offline
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Join Date: Mar 2007
Location: Blue Springs, MO
Posts: 230
Default Re: A/C units

Originally Posted by fmagdefrau View Post
Why do you not operate central a/c units when the temperature is below 65 degrees outside? Also will they even come on when it is 32 degrees outside?

Its normally 60* not 65*

and you been a home inspector since when? hows your liability insurance?

David Moriconi, CMI
M3 Real Estate Inspection, LLC
iNACHI Certified Residential Inspector
NRSB Certified Radon Measurement Specialist
IAC2 Certified Mold Inspector
Missouri and Kansas Termite Licensed
Infrared Certified
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Old 2/21/10, 7:45 PM
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Buck Hartley, CMI Buck Hartley, CMI is offline
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Join Date: Nov 2005
Location: Merriam, Kansas
Posts: 1,965
Default Re: A/C units


Be NICE, I know that it has been a LONG old winter!

Mid America Property Inspections, Inc.
Shawnee, KS 66216
NACHI # 05110992
KS-Radon Cert.# KS-MS-0035
KS-Termite Cert. # 18933
M0-Termite Cert. # N 5033

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Old 2/21/10, 9:50 PM
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mklein mklein is offline
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Join Date: Dec 2009
Posts: 91
Default Re: A/C units

I believe that the 60 degree limitation has a couple of reasons. First and foremost, some manufacturers state specifically that their units should not be operated when outdoor temperatures are below 60 because "the unit will cycle excessively and damage the fan cycling switch." I have also read that the cooling coil can frost up, which might not be a problem as long as the defrost goes the right way.

But, I have also heard that the compressor could be damaged if its heater is not working properly, and possibly even if it is. In a cooled state, the Freon could mix with the oil in the compressor. The heater helps keep the oil warm to keep the Freon as a gas. If it is in liquid form, it can slug and damage the compressor.

So, I guess the bottom line is you might be able to run a compressor with outdoor temps below 60 for a VERY short time. However, I would not recommend it if the unit is less than 5 years old so that you don't screw up someone's warranty. I would especially not do it for a buyer client without the homeowner's permission because you know who is going to pay for the repairs if damage is done. And finally, you might not even be able to run the unit if it has protective controls installed. If the unit doesn't work because of the controls, some inspectors might say that the unit needs repair when it doesn't.

Matthew Klein, P.E., M.B.A.

Criterium Engineers

PO Box 181503
Cincinnati, OH 45018-1503
Phone: 513-474-9600
FAX: 888-747-0427
E-mail: Criterium-Cincinnati@fuse.net
Website: www.Criterium-Cincinnati.com
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Old 2/22/10, 10:49 PM
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Richard W. Washington, TREC#7238 Richard W. Washington, TREC#7238 is offline
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Join Date: Jul 2004
Location: West University Place, TX
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Default Re: A/C units

I just tell the client that the condensing unit oil cannot circulate properly and will pool in cooler temperatures and if it is operated will damage the unit at temps below 60 F. Also offer to come back at no charge if they want me to inspect it when it is cooler.

Richard W. Washington, owner
RW Home Inspections, Inc.
Texas Real Estate Commission (TREC)
Professional Inspector License #7238
Texas Professional Real Estate Inspectors Member (TPREIA)-Greater Houston Chapter
InterNACHI member since 2004
Based in Katy, serving Houston and all surrounding communities
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