a/c start-up in cold weather

jodem · October 31, 2007, 01:37:15 PM

Is there some type of chart to determine proper charge in cold weather when installing a/c equipment?

TECH X · October 31, 2007, 05:56:14 PM

I would just induce your readings. Use something to cover the top of the outside unit but leave the condenser coil exposed. If it's a R22 system, cover up the discharge air until you can maintain 200 PSIG on your high side. If it's a 410A system induce the high side to 325 PSIG. The low side pressure should react and you can calculate your superheat or sub cooling.

I've never had any problems doing this. It beats re scheduling the call to wait for warm weather.

acefurnacefixer · November 04, 2007, 06:54:10 AM

QuoteI would just induce your readings. Use something to cover the top of the outside unit but leave the condenser coil exposed. If it's a R22 system, cover up the discharge air until you can maintain 200 PSIG on your high side. If it's a 410A system induce the high side to 325 PSIG. The low side pressure should react and you can calculate your superheat or sub cooling.

I've never had any problems doing this. It beats re scheduling the call to wait for warm weather.

Thats not true, I am not calling you a liar you may just be mis-informed. the tarp will give you false readings. you can do a aproach charge or check sub cooling in lower ambiant temps. Also all CU come with a crankcase heater or they use a single pole contactor leaving 1 leg hot to the compressor at all times. Also If the unit has to run regularly in low ambiant conditions, its a good idea to install a fan cycler

oldguy2 · November 04, 2007, 08:23:21 AM

they have charts for cold weather start ups i have theses charts if i knew how to put them on here i would. you need to crank up the heat before you get there tell the home owner to raise the temp up in the house.its cuz u need a heat load,u can simulate a 80 degree day wrap the condenser until your head pressure is where it should be then do your then do your superheat check.the charts show you what your super heat and subcool should be before you even put your gauges oneven tells you what your td should be like i said if i knew how to post them charts on here i would got them from a hvac lennox school

ProTemp · November 06, 2007, 03:36:54 PM

Quote from: acefurnacefixer on November 04, 2007, 06:54:10 AM

Thats not true, I am not calling you a liar you may just be mis-informed. the tarp will give you false readings. you can do a aproach charge or check sub cooling in lower ambiant temps. Also all CU come with a crankcase heater or they use a single pole contactor leaving 1 leg hot to the compressor at all times. Also If the unit has to run regularly in low ambiant conditions, its a good idea to install a fan cycler

This will put an end to this post and hopefully answers the original question. Low amb start up can be performed if you have M.O.P.D. To achieve this you must induce your pressures. If you do not have Your MOPD, you ill not get the proper amount of liquid refrigerant entering the metering device (orifice) wich will starve the evaporator. In refrigeration theory you require 100 psig across the low side and high side to get a proper cooling effect. As for crankcase heaters its important for continuous low amb use (heat pumps). For regular a/c once a year start up or maintenance will not damage the compressor. Please do not respond with efficiency ratings or other readings that you googled to try and contradict this post. Low amb start up can be performed if done properly. Tarp or cover the unit. Try to achive 200 psig (105 deg) on the high side and 70 psig (40deg) on the low side. If you achieve these readings you off to the races. For superheat and sub cooling values are trivial at this point. Once again please do not post a reply to contradict these values.....thank you

Admin · January 30, 2014, 02:00:23 PM

You can download an interesting on cold weather startups - Here

Trainerguy · February 01, 2014, 05:30:00 PM

The only proper way to determine the exact charge is to weigh it in. The rating plate will tell you the total charge usually for the outdoor unit, the indoor coil, and 15 ft. of liquid line. if the line set is longer you would add extra according to the size of the liquid line. The manufacturers instructions will tell you how much. And don't forget the charge for the drier that you have to install.
Trainerguy