the 65 degree question

[cbrands]

can someone supply some good solid literature on why you should'nt run the AC when temps are too low?

looking to have ammo when i'm confronted.

opinions and/or personal practices also welcome.

[gkoehl]

Originally Posted by cbrands

can someone supply some good solid literature on why you should'nt run the AC when temps are too low?

looking to have ammo when i'm confronted.

opinions and/or personal practices also welcome.

I believe it is HeatPumps that shouldn't be tested in cooling mode under 65
AC's are not tested under 60 (some HI make a practice not to test if the temp has dropped below 60 (for an extended period of time) in the last 24 hours or if the unit has not been energized for the past 24 hours).

The best argument would be your SOP
and the fact that most Inspection (Orgs and State) SOP's recognize the possibility of damage to a AC unit if operated when conditions are not conducive to testing.

I.E.= Industry standard argument

[jwortham1]

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.

[Charley L. Bottger]

Originally Posted by cbrands

can someone supply some good solid literature on why you should'nt run the AC when temps are too low?

looking to have ammo when i'm confronted.

opinions and/or personal practices also welcome.

Don't have any literature but have a head full experience.

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

If this sounds like Greek I can try another approach.
</IMG>

[jwortham1]

Nice.

Learn something new everyday!

[lewens]

Originally Posted by jwortham1

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.

Jeffery
It may only be semantics but a liquid cannot be compressed.
Larry

[jwortham1]

Larry,

Per the US Dept. of Energy:

Question - Why does air compress and why does liquid not compress?

Gases, like air, consist of molecules separated from each other, bouncing
around. In a liquid, the molecules are all touching. Compressing a gas
simply forces the molecules to come closer to each other. If a gas is
compressed enough, or cooled enough, the molecules will pack right next to
each other, condensing into a liquid or a solid. It is hard to compress the
condensed matter further.

Liquids actually can be compressed somewhat. It is just a lot harder than
compressing gases, that is, it takes a lot more energy to reduce the volume
of a liquid than to reduce the volume of a gas by the same amount. Solids
also can be compressed, but since they are condensed phases too, it takes
much energy.

Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois

[cbrands]

Originally Posted by cbottger

Don't have any literature but have a head full experience.

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

If this sounds like Greek I can try another approach.
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doesnt sound greek to me.

you mention the MFG states no running the unit under 60 degrees.
All or most MFG's?

crankcase heater...how would i know if a unit has one?
newer technology or older one?

now the big question...what's everyone's threshold on not running ac units due to outside temps?

[Matt Berman]

I will not start any ac unit if the ambient (outside) air temperature is below 65 degrees and if it has not been started at least once by the seller or sellers agent. Experience tells me it could break down on an initial start up and i dont want to buy an ac unit for someone else.Just my policy.Matt

[Charley L. Bottger]

Originally Posted by cbrands

doesnt sound greek to me.

you mention the MFG states no running the unit under 60 degrees.
All or most MFG's?

crankcase heater...how would i know if a unit has one?
newer technology or older one?

now the big question...what's everyone's threshold on not running ac units due to outside temps?

I think you will find that all MFG recommend not to operate at below 60 degrees this can vary within different SOP's per your State. My SOP states 60 degrees. Generally speaking if the outside ambient is below 60 degrees you will be getting squirrelly temps on the unit anyway won't tell you much of any thing other than it starts.

Crankcase heater have been around since Mobey Dick was a Minnow

Two kinds the stainless steel band around the bottom of the compressor with two wires going back to the top side of the contactor as this heater requires 220-volts when the unit is shut down.

The second kind is embedded within the crankcase of the compressor and all you will see are two wires that appear to disappear into the metal housing of the compressor at the bottom. Both kinds of heaters will be activated in the off cycle of the unit.

[Charley L. Bottger]

Originally Posted by lewens

Jeffery
It may only be semantics but a liquid cannot be compressed.
Larry

I beg to disagree what do you suppose a water pump does when it increases the pressure from say 25 PSIG to 150 PSIG it compresses the liquid??????

[Vince Santos]

Originally Posted by mberman

I will not start any ac unit if the ambient (outside) air temperature is below 65 degrees and if it has not been started at least once by the seller or sellers agent. Experience tells me it could break down on an initial start up and i dont want to buy an ac unit for someone else.Just my policy.Matt

If the temperature is as you stated I would think the unit breaking down at startup would fall under failed under testing.

If a garage door comes off the track when you open it are you responsible for fixing it?


I never check the units if the outside temperature has been under 60% within a 24 hour period.

[Charley L. Bottger]

Originally Posted by mberman

I will not start any ac unit if the ambient (outside) air temperature is below 65 degrees and if it has not been started at least once by the seller or sellers agent. Experience tells me it could break down on an initial start up and i dont want to buy an ac unit for someone else.Just my policy.Matt

Matt that is just fine you made the decision to choose 65 degrees just stick with it. be consistent.

I personally have operated in my other life units that were serving commercial areas with no windows that had high sources of heat generated from within the building and A/C units were operated 365 starting and stopping with an outside ambient at zero some with crankcase heaters some without. There is no rule that says Puff the magic dragon the valves will blow if you start this unit in temps below 60 or 65 as an HI pick a temp and just stay with it.

[Charley L. Bottger]

Originally Posted by vsantos

I never check the units if the outside temperature has been under 60% within a 24 hour period.

Vince thats fine if you made this decision but can you explain why you choose those numbers.

[Russel Ray]

Originally Posted by vsantos

I never check the units if the outside temperature has been under 60% within a 24 hour period.

What's with the "24 hour period"? That sure would preclude everyone in the desert mountains between, say, here and El Paso from using their cooling systems since it regularly gets down to 40° at night and up to 90° during the day. If I had those inspection protocols, I would never be able to test the cooling systems here. Hmmmmmm. Certainly would make the inspection go faster.