Written compressor operating envelopehigh pressure cut off switch,Written A few years ago 45-50degC was the threshold upto which the AC's used to provide cooling. Now there is a fair bit of technical portion related to it.The AC operates in two pressure A high Pressure (The Condenser / Outdoor Unit) and a low pressure side (The Evaporator / Indoor Unit). Now the condenser has refrigerant flowing inside it which must have temperature greater than the ambient temperature to facilitate Heat Exchange(Heat always flows from Higher Potential to Lower). As the ambient temperature increases the temperature of the refrigerant must increase. To increase this we must increase the pressure which is only possible by increasing the compressor capacity. So what the manufacturers do is they change the refrigerant itself. Now this refrigerant has different properties and has a higher temperature at the same pressure. Thus AC's can even perform at high temperatures. As far as I know the current maximum temperature upto which AC's can operate is 55-60 degC.

Now it might also depend on the geographical location too.Written Air Conditioner(lit: cooler)is a heat pump. For 'pumping' the heat out, you need the 'sink' viz. the outside air be at a temperature lower than the saturation temperature(condenser) of the refrigerant.A simpler suggestion - also hygienic, but expensive - is to recycle the room air to cool the condenser. However, the temperature drop depends on the rating of the machine and of course, the insulation of the room which incidentally, determines the lowest temperature that can be attained.placement of ac unit the 65 degree questionreviews of hvac units can someone supply some good solid literature on why you should'nt run the AC when temps are too low?best ac unit brands india looking to have ammo when i'm confronted.

opinions and/or personal practices also welcome. Re: the 65 degree question 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 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. Learn something new everyday! It may only be semantics but a liquid cannot be compressed. 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. 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??????

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. StepByStep Home Services LC Providing Home Inspection Services to Southeast Michigan ITA Trained and Certified Matt that is just fine you made the decision to choose 65 degrees just stick with it. 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. Vince thats fine if you made this decision but can you explain why you choose those numbers.