Determining correct charge on cool days

[squirrelshot]

Yep I'm a newby, but got a question for you more experienced techs. During this time of year a customer may be using AC one day and heat the next. If you need to check AC charge on a cool day, is there a different process to do this? Or, do you just slap gauges on and look at PT Chart? Also, should superheat and subcool targets be the same when you are so far away from design condition temps? Thanks for any help yall!

[toocoolforschool]

There has to be some kind of load to determine sub and super heats.

[hotrodrob]

you can simulate a warmer day by raising head pressure by blocking some of the outdoor coil. as long as you have a decent load on the indoor you can get pretty close with your SH/SC.

[SBKold]

Metering device is important as txv will react different from fixed.

[squirrelshot]

Metering device is important as txv will react different from fixed.

Thanks to all the suggestions...

So, really it sounds like its better to evaluate the system when there is a heat load I.D....then be sure to follow proper protocol per TXV or F.O.

[sabur2121]

The only way to properly charge the system on a cool day is to raise the head pressure along with wet bulb, dry bulb, pressure and temperature checks. Of course this depends on TXV or Fixed Orifice. Once you have all your numbers you should charge according to the subcooling (if TXV) or superheat (if Fixed) that comparable to the numbers. This is important because the numbers change with the temp.

[mark beiser]

If the indoor wet bulb temperature is below about 55ºF, you can pretty much forget about checking the refrigerant charge with any degree of accuracy.
You really need to start with it higher than that, because you need the system to run long enough to stabilize, and especially with fixed metering, the coil to get wet.

[JUSTADDSOMEMORE]

Wrap your OD coil with plastic and get your head pressure up around 250, and check like normal. Some Indoor load is ideal but not always possible. I believe in checking subcool and superheat regardless of txv or fixed. Subcool will let you know you have plenty of liquid and superheat with let you know your compressor protected .

[ch4man]

you know blocking the outdoor coil changes the design temperature of the coil.

check out Jim Bergmans videos hawking the fieldpiece charging blanket. does a good job of explaining the science of why blocking inlet airflow to raise head pressure is not the best idea.

[jason12000]

I was going to ask if the flashing ad to the right of the screen about the field piece jacket has been tested in the field or not? Thanks ch4man.

[squirrelshot]

you know blocking the outdoor coil changes the design temperature of the coil.

check out Jim Bergmans videos hawking the fieldpiece charging blanket. does a good job of explaining the science of why blocking inlet airflow to raise head pressure is not the best idea.

Thanks for the tips yall- ch4man- I went on Youtube and could only find one Jim Berman vid on fieldpiece charging blanket, but he seemed to be speaking pretty positively about how it worked....had it all mapped on his laptop showing HP and corresponding changes in SC...pretty interesting. Did you see a different one? Thanks