Correct Charge??? R407c

[airflo]

Hello,

Ok im a i 1st year tradesman fridgy i have done commercial a/c installation my whole trade and only now am i starting to do some service work. Previously if i need to check the refrigerant charge on an a/c unit i would take the superheat and adjust accordingly (only ever used R22 which i usually use a 8k TD).

Now i'm starting to do some service i came across a R407C charged a/c unit which i needed to check the charge on? now i have a few questions.

1) what superheat should i be looking for?
2) how would i check for correct charge if the unit was on heating? (the only gauge ports are outside the unit on the service valves).
3) in the future if i come across different types of refrigerant how do i know what superheeat i should be looking for?

Any help would be great?

[nike123]

Hello,

Ok im a i 1st year tradesman fridgy i have done commercial a/c installation my whole trade and only now am i starting to do some service work. Previously if i need to check the refrigerant charge on an a/c unit i would take the superheat and adjust accordingly (only ever used R22 which i usually use a 8k TD).

Now i'm starting to do some service i came across a R407C charged a/c unit which i needed to check the charge on? now i have a few questions.

1) what superheat should i be looking for?


You say that you are working on commercial A/C units. They usually have TXV and liquid receivers. They should be charged by sight glass and subcooling method. If you have TXV he tries to keep superheat at set value and therefore you cannot charge them by superheat.


Check this article! (http://tinyurl.com/56jrzl)

Pressures in this article are for R22, if you want to convert them to R407C you should find corresponding saturation temperatures for R22 and then convert that temperatures in pressures for R407C. Be careful to use correct saturation liquid or gas temperatures for R407C for superheat and subcooling (temperature glide issue).


2) how would i check for correct charge if the unit was on heating? (the only gauge ports are outside the unit on the service valves).
Recover and weigh refrigerant. Or you could always measure indoor unit capacity by measuring air flow and dT of indoor unit (or by entering manufacturer data about air flow after thorough cleaning).


3) in the future if i come across different types of refrigerant how do i know what superheeat i should be looking for?Superheat and subcooling should be the same no matter of refrigerant type.

[airflo]

Hello,

Thanks for your responses :)

Sorry i previously worked on commercial A/C units doing just installation........no commissioning or troubleshooting.

Ok so for my superheat i should just use a 8k TD between suction line temp & suction line guage temp (using pt chart)???

Im unsure on how to use the subcooling method could someone explain please???

The units im servicing now are domestic A/C units so they have no sightglass......but i do know how to charge using the sightglass if need be.

Thanks in advance.......airflo

[airflo]

by the way nice article, i have printed it out and will read through it tonight.

[nike123]

Hello,

Thanks for your responses :)

Sorry i previously worked on commercial A/C units doing just installation........no commissioning or troubleshooting.

Ok so for my superheat i should just use a 8k TD between suction line temp & suction line guage temp (using pt chart)???


No, superheat value is not fixed, you first need to find correct superheat for your conditions on site, and then charge until you meet that superheat. Table in article gives you targeted suction pipe temperature but you should convert evaporation pressure for R22 in to saturation temperature. Then you could use that temperature values for any refrigerant.
Use table for high efficiency.


Im unsure on how to use the subcooling method could someone explain please???It is explained in article as well as superheat method.
Best method for domestic split-type air conditioner is to recover refrigerant and weigh recovered amount to establish is there charge problem and then charge correct amount (stated at A/C nameplate) by weight.

[Arc]

Unfrotunatley all I ever see is 22 and was taught the old school ways of charging as mentioned previously. When contacting manufacturers is it simply the superheat or subcooling figures required, what else do you ask for without sounding like an idiot when trying to achieve the perfect charge?

[nike123]

Unfrotunatley all I ever see is 22 and was taught the old school ways of charging as mentioned previously. When contacting manufacturers is it simply the superheat or subcooling figures required, what else do you ask for without sounding like an idiot when trying to achieve the perfect charge?

You ask for charging table (by superheat for capillary as expansion device) if available, or amount of subcooling for TXV, but mostly all of them would say to you to charge by weight.

As I said before, don't do it by superheat or subcooling. Do it by weight. It is faster and more accurate on domestic split-systems.
And, most of the time, it is idiot-proof.:D