TREC SOPS AC Inspection at 60 F.

[imported_John Smith]

As a good working AC system is a high priority for home buyers in Texas, many seem disappointed if you tell them you cant operate the system when the temperature is hovering around 60 F. It seems to be coming up a lot lately for me, and Im not sure if Im just being paranoid. If the outside air temperature is 65 F, obviously the compressor could be colder assuming the overnight temperature is < than 60 F.

How do my more experienced peers handle this?


TREC Reference
"The inspector shall: operate the system using normal control devices except when the outdoor temperature is less than 60 degrees Fahrenheit"

[Jim Luttrall]

You are NOT being paranoid.
A compressor can be damaged or destroyed when operated in cold temperatures.
Most manufacturers will have a blurb in the manuals about 55 or 60 degrees.

One other thing that is missed by HI's (as far as I can tell) is the prohibition of starting a compressor if power has not been on to the condensing unit for 12 hours or so.
Both conditions can cause "slugging" where liquid refrigerant migrates to the cold compressor and is sucked into the intake valves and cylinder(s) of the compressor.
Liquid does not compress very well, tends to break pistons, rods, and discharge valves.

Since I have a background in A/C, I tend to push the envelope, but I would not recommend it.

It is just like if there is snow on the roof, or the power is off, you can't inspected what you can't inspect.
BTW, an A/C tech can't operate it when it is cold either.

[Rick Hurst]

John,

The client will be much more disappointed once they move in and have to perform possible repairs just because you turned on the equipment to show them it operated.

That alone does not prevent a visual inspection of the equipment to look for other defects or issues.

As Jim said, at those lower exterior temperatures your not going to determine if the equipment is cooling properly anyway.

Sometimes after you have explained all the reasons to the client, the agent will go behind you and turn on the thermostat and take the client outside of say, See its running. :rolleyes:

rick

[Jerry Peck]

Jim,

I had always heard it as 'lower than 60 degrees for the previous 24 hours'.

That would mean it could have been 60 or above during the previous day and it would still be okay to turn it on.

Was that old way of saying it correct, or is it 'if it is *now* less than 60 degrees, do not operate it (unless, of course, it is a heat pump).

[Bruce King]

The part about the "12hr power on" assumes a crankcase heater is present.

Also, many manuf's require the period to be 24 hours but then again, assuming a crankcase heater is installed.

These are not installed in many areas.


My bryant/carrier heat pump unit says no heat above 66 deg and no A/C below 55 deg. It actually prevents cooling automatically via the outside air temp sensor installed when its lower than 55 deg.

[Jim Luttrall]

There is a lot of difference of opinion and instruction from manufacturers on this.
To err on the side of safety, 24 hours above 60.
I personally take into account the previous nights temperatures, what side of the house the unit is on (sun or shade), what the current temperature is, and whether I'm feeling lucky;) .
But Rick said it right, you aren't going to prove much about the performance when it is close to the limit.
It just is not worth the risk.
Most of the time there is other problem with the system that I recommend service anyway, and I am not bashful about telling them it is too cold to test the unit.

Bruce is right about the 12 hour period of power is for crankcase heaters. Not all units have them, but I am seeing lots of stickers on the units lately.
If the units have crank case heaters, the heat keeps the liquid refrigerant from migration to the compressor pot.

[imported_John Smith]

Ill show my stupidity. I realize my trucks AC takes a different refrigerant than my house AC. Other than that, I thought they operated pretty much on the same physics. When I turn my truck defrost on, at 40 F or so, I dont damage the AC system.

[Jim Luttrall]

Your truck does not have a pot compressor (welded hermetic compressor) that the refrigerant migrates to because it is the coldest part of the system.
The automotive systems are designed for all weather operation (similar to heat pumps) in a number of different ways, including suction line receivers or other methods.

[Scott Patterson]

If you have a Scroll design compressor they can run at just about any temperature without causing damage to the unit. I know, my wife has our on right now and it is 46f outside! But, MaMa is happy!

[JB Thompson]

I'll always defer to the AC experts above, but I'll tell you on the sly that I've been a fireman for 21 yrs and we (not me, these other 'uns) run the AC when it's substantially lower than 60 outside. I've come to work many times in the winter with station temp really cold -- colder than outside. The city buys cheap units and I'll be danged if we don't run them through the gauntlet. They seem to last year after year.;)

Bruce

[TOM DEEHAN]

I work in the residential HVAC service business and have the luxury of starting up and do seasonal maintenance checks on A/C systems. I've done them in all kinds of temperatures (up there in the great white north)and have never damaged a system. If the temp is below 65 try running the A/C with a plastic bag over half of the condenser coil, it drives up the head pressure and simulates a hot day. You can then impress your client and do what ever checks you want to do and the system won't freeze up.

Crank case heaters are only found on heat pumps now. On A/Cs they use a single pole contactor to control the A/C which means there is 120 volts being supplied to the compressor windings which heats up the windings just enough to boil any refrigerant out of the compressor sump.

Scroll compressors can take just about anything. No valves or pistons.
scroll compressor (http://www.indoorclimate.com/hvac_info/scrollcompressor.htm)

Tom

[Jim Luttrall]

Tom, have you ever heard a compressor slugging liquid? Not a pretty sound.
The damage does not come from running the system, it is from STARTING the system when refrigerant has migrated to the compressor.
Once it is running, the danger is pretty well past.
Blocking the coil to elevate the head pressure is a useful tool to simulate a warm day, but won't help a bit to prevent damage during start-up.

[Matt Fellman]

Aside from the debate you guys are fortunate to be having it in the middle of January. I have at least 3 more months before I have to think about it...

[JB Thompson]

I've got a question. What happens when it is a heat pump? Isn't the coolant still sitting outside when the unit comes on? Wouldn't it be sluggish eventhough it is running the other direction?

Ignorantly,
Bruce

[Jim Luttrall]

Heat pumps are created to run in cold weather and have provisions to deal with the liquid.

Crank case heaters are one option, they are a low wattage heater that keep the compressor warmer than the interior coil during the off cycle, preventing the refrigerant from migrating to the compressor.

Some straight A/C units have these and you may see a little warning sticker telling you not to run the compressor for 12 or 24 hours once power has been restored.

This is designed to give the low wattage heater a chance to heat up sufficiently to drive the liquid refrigerant out of the compressor to prevent start-up damage.

A more common method is a suction line accumulator and as has been mentioned and the scroll compressor.

[Jim Luttrall]

By the way, the refrigerant is not sluggish, it moves quite well even in sub-zero temperatures.
The term "slugging" liquid refers to the introduction of a large quantity of liquid "a slug" into the compressor cylinder. Think of the old westerns when the cowboy tilts his head back and takes a "slug" of liquor.

[JB Thompson]

Thanks Jim.

[JB Thompson]

Jim, while I'm thinking of it...

Earlier in this thread I mentioned that the AC's at the fire station run in very cold weather. In your opinion, why don't we have any problems with these units?

Bruce

[Eric Barker]

This is on my 5 yr old Trane compressor.

A little blurry, too lazy to actually go outside so I took this reaching out the window.

[Jim Luttrall]

Jim, while I'm thinking of it...

Earlier in this thread I mentioned that the AC's at the fire station run in very cold weather. In your opinion, why don't we have any problems with these units?

Bruce

JB, those could be spec'd to have crank case heaters, or you could just be lucky.
If the units are not off long enough for the motor to cool down, then the migration process won't happen. I have operated bunches of units in cold weather, but I have also been there when slugging takes place and just the noise is enough to make you run for cover!
I see you are also down in Tyler, the warmer the climate, the less the chance of liquid migration. Of course if you keep the fire house really cold, there will be less temperature difference between indoors and outdoors.
Bottom line, I don't know in this case.

[JB Thompson]

JB, those could be spec'd to have crank case heaters, or you could just be lucky.
If the units are not off long enough for the motor to cool down, then the migration process won't happen. I have operated bunches of units in cold weather, but I have also been there when slugging takes place and just the noise is enough to make you run for cover!
I see you are also down in Tyler, the warmer the climate, the less the chance of liquid migration. Of course if you keep the fire house really cold, there will be less temperature difference between indoors and outdoors.
Bottom line, I don't know in this case.

I understand. BTW, I'm a fireman in Dallas; I live in Tyler.

[Blue Harriss]

So for those of you who do not check the AC in lower temps, do you charge to come back out and check if the weather pemits. I see this a lot in NC where the weather is constantly changing. There is a very strong chance that in any 4 week period there will be a time when the AC can be checked. If you do charge, how much just for an AC check?

Thanks

Blue Harriss

[JB Thompson]

So for those of you who do not check the AC in lower temps, do you charge to come back out and check if the weather pemits. I see this a lot in NC where the weather is constantly changing. There is a very strong chance that in any 4 week period there will be a time when the AC can be checked. If you do charge, how much just for an AC check?

Thanks

Blue Harriss

I personally don't go back out. However, no one has asked me to either. I also don't get on a roof in the rain and I don't go back out to check it either. Probably not the answer you're looking for.

Bruce

[Blue Harriss]

I usually don't get asked either but have been three times in the past month. None have been a problem and have worked out perfect in my schedule but it looks like this will be a trend. And since there are way too many inspectors in this area and too few closings I kind of see it as a value add, but my time should have some value.

Blue Harriss

[JB Thompson]

I agree. If you can fit it in to your schedule and drive, then doing a good job and customer service are certainly the keys to separating yourself from the competition.

I just have never had anyone ask.

[Jim Luttrall]

I have only been asked a couple of times to go back since if it is too cold on the day I'm there, there is a good chance that the weather will not change enough to allow operation before their option period is up. I have gone back on occasion for no charge if it is close by, no way I can drive an hour or more for free though. Kind of like snow on the roof, I can't control the weather.:D

[Billy Stephens]

Gentlemen,

Please remember to document your actions. ;)

Sorry pdf was all I had.(2 system home.)