The theory of charging an R22 system without a TXV

[udarrell]

if you like english beer beer can cold can be prety close

A heavy indoor humidity load tosses the beer-can-cold non-sense out the window.

The outdoor dew point determines at what temp the suction line sweats; that's fools gold methodology...

[Chuck]

I will differ with the previous responses somewhat. Where the manufacture tables/ guidelines are unavailable, I was taught to use data from the compressor manufacturer as different compressor MFG's want different things. Remember that we want enough cooling capacity to return to the compressor for the windings.
On a fixed metering split system where would you go for compressor manufacturer specs? Some days you will have 25 SH and some days only 5 SH

Another method where no other data exists would be measurement of system output vs rated capacity (if available) or simply optimizing capacity & efficiency. Most residential techs/clients wouldn't have enough patience for that, but it would serve as a valid method.
This is a great plan! Kind of hard to get the specs sometime, especially when you are not at ARI design conditions.

In my mind I would NEVER, NEVER use a weigh in charge as the optimal method on a split system design. Refrigerator, yes. AC? no. While the method certainly exists I've never read a install manual that suggested it is the preferred method for AC, unless we are talking mini splits. I would however use it as a diagnostic tool if necessary.

My comments in red.

I agree with your last paragraph, too many variables to use weight as the final answer for the correct charge.

[udarrell]

Just curious,,,

On a new install, the outdoor unit (in this case Trane xLi16) contained the proper system charge for the complete system (including some amount of linesset)????

So the install tech brazes everything together, pumps down the lines, and then opens the valves on the outdoor and you're good to go....no extra charge unless lineset is over X feet...

Is this correct??

Always, before the charge is checked the correct airflow through the indoor coil must be checked & confirmed & documented for the customer's records.

[darctangent]

My comments in red.

I agree with your last paragraph, too many variables to use weight as the final answer for the correct charge.

As to the first item-

If you are looking for a fixed # then you need the condenser to be operating in a fixed environment, and most resi AC condensers have a design condition of 90F ODT. The fixed SH value for a compressor can be had directly from the MFG via support. I don't believe copeland has specs in their product literature but that could have changed. keep in mind that one might be able to play with that figure a little depending on the environment conditions the system is installed in. ie- Yuma and Seattle are two different scenarios.

[HVACTechNC]

So am I mistaken that most major manufacturers recommend weighing in additional refrigerant on unit start-up. I am almost 100% certain that both Rheem and York on their installation manuals have a supplemental charge section that gives weight by line set size and length.

I am all for checking the superheat and subcooling on system test to verify proper operation, in fact you would be doing the customer/system a disservice to just weigh in a charge and not verify it. all I'm saying is that the manufacturer recommends weigh-in as their preferred method.

[54regcab]

On systems that have been in service for a few years how does dirty condensers/evaporator coils factor in?

[fearlessfurnace]

A heavy indoor humidity load tosses the beer-can-cold non-sense out the window.

The outdoor dew point determines at what temp the suction line sweats; that's fools gold methodology...

british ale is drunk at 60F more ore less. Thats 40F evaporating temp plus 20F superheat.

[darctangent]

On systems that have been in service for a few years how does dirty condensers/evaporator coils factor in?

You forgot dirty blower wheels and bad duct design along with poor to no effort to dial in airflow, but the answer is plenty.

[fearlessfurnace]

On systems that have been in service for a few years how does dirty condensers/evaporator coils factor in?

If the coils are dirty the system can't run right clean them first. b
Bad coils will drop the superheat on a fixed orifice so the balanced charge will be less refigerant.

[54regcab]

Of course cleaning the coils (especially the condenser) should be done before charging, but how many techs actually do this? And then there is the blower wheel/low airflow issues, are these also addressed before determining correct charge?

On my system the indoor humidity goes up when the condenser coil gets dirty. It doesn't LOOK dirty, but cleaning it drops the humidity. Maybe the indoor coil is getting colder due to the clean condenser?

[Chuck]

Of course cleaning the coils (especially the condenser) should be done before charging, but how many techs actually do this? All the good ones.

And then there is the blower wheel/low airflow issues, are these also addressed before determining correct charge? If the homeowner agrees to pay for it.

My comments in red.

[darctangent]

Of course cleaning the coils (especially the condenser) should be done before charging, but how many techs actually do this? And then there is the blower wheel/low airflow issues, are these also addressed before determining correct charge?

As to cleaning the condenser, yes it comes part and parcel with my work and is covered under my annual maintenance charge that is typically added as part of the repair unless I know that it's clean.

With 1000+ posts, I should ask, are you a pro or what?

[54regcab]

As too cleaning the condenser, yes it comes part and parcel with my work and is covered under my annual maintenance charge that is typically added as part of the repair unless I know that it's clean.

With 1000+ posts, I should ask, are you a pro or what?

Not a HVAC pro, but as you see I've been on here 10yrs. Actually I repair TV's and Appliances for a living, HVAC is a interest/hobby of mine. I looked into doing HVAC for a living but I can't work minimum wage while I "pay my dues" as a installer/ductwork guy. I understand most trades require "paying their dues (mine included), but the time to be moved from installer to a well paid tech is too long. As a TV/Appliance tech the electrical stuff comes relatively easy to me, it's the refrigerant stuff I'd have to get field experience with. I could even repair the control boards if it's economically feasible, although if it's like TV/Appliances these days it's more cost effective just to replace the board.

[darctangent]

Not a HVAC pro, but as you see I've been on here 10yrs. Actually I repair TV's and Appliances for a living, HVAC is a interest/hobby of mine. I looked into doing HVAC for a living but I can't work minimum wage while I "pay my dues" as a installer/ductwork guy. I understand most trades require "paying their dues (mine included), but the time to be moved from installer to a well paid tech is too long. As a TV/Appliance tech the electrical stuff comes relatively easy to me, it's the refrigerant stuff I'd have to get field experience with. I could even repair the control boards if it's economically feasible, although if it's like TV/Appliances these days it's more cost effective just to replace the board.

Commercial controls would be your best bet as a point of entry, if that was your choice.

As an aside, I would say tv repair would be a tough trade to do well in. While I realize it's far more centralized than days of old, you are always battling against the cost of replacement. Seems like medical equipment would be the better gig.

[hvacrmedic]

So am I mistaken that most major manufacturers recommend weighing in additional refrigerant on unit start-up. I am almost 100% certain that both Rheem and York on their installation manuals have a supplemental charge section that gives weight by line set size and length.

I am all for checking the superheat and subcooling on system test to verify proper operation, in fact you would be doing the customer/system a disservice to just weigh in a charge and not verify it. all I'm saying is that the manufacturer recommends weigh-in as their preferred method.

Rheem doesn't say that it's their preferred method. See the attached Installation manual below. Page 14.

Goodman doesn't even cover weighing in the charge in the second of the two attached manuals.

Just saying.

[darctangent]

Rheem doesn't say that it's their preferred method. See the attached Installation manual below. Page 14.

Goodman doesn't even cover weighing in the charge in the second of the two attached manuals.

Just saying.

actually, page 6 of the goodman manual:

Adequate refrigerant charge for a matching evaporator and 15
feet line set is supplied with the condensing unit. If line set
exceeds 15 feet in length, refrigerant should be added at .6
ounces per foot of liquid line.

[fearlessfurnace]

Of course cleaning the coils (especially the condenser) should be done before charging, but how many techs actually do this? And then there is the blower wheel/low airflow issues, are these also addressed before determining correct charge?

On my system the indoor humidity goes up when the condenser coil gets dirty. It doesn't LOOK dirty, but cleaning it drops the humidity. Maybe the indoor coil is getting colder due to the clean condenser?

yep

[hvacrmedic]

actually, page 6 of the goodman manual:

Adequate refrigerant charge for a matching evaporator and 15
feet line set is supplied with the condensing unit. If line set
exceeds 15 feet in length, refrigerant should be added at .6
ounces per foot of liquid line.

That is not the weigh in method per se. It only covers the additional lineset charge, and is not intended to be "the" charging method. That passage is followed immediately by,

"FINAL CHARGE ADJUSTMENT
The outdoor temperature must be 60°F or higher. Set the room
thermostat to COOL, fan switch to AUTO, and set the temperature
control well below room temperature.
After system has stabilized per startup instructions, check
subcooling and superheat as detailed in the following section."

[darctangent]

That is not the weigh in method per se. It only covers the additional lineset charge, and is not intended to be "the" charging method. That passage is followed immediately by,

"FINAL CHARGE ADJUSTMENT
The outdoor temperature must be 60°F or higher. Set the room
thermostat to COOL, fan switch to AUTO, and set the temperature
control well below room temperature.
After system has stabilized per startup instructions, check
subcooling and superheat as detailed in the following section."

Completely agreed.

It is covered under "initial charge" which to me is the same thing as guesstimate. I actually find that typically overcharges the system.

[ryan1088]

Not a HVAC pro, but as you see I've been on here 10yrs. Actually I repair TV's and Appliances for a living, HVAC is a interest/hobby of mine. I looked into doing HVAC for a living but I can't work minimum wage while I "pay my dues" as a installer/ductwork guy. I understand most trades require "paying their dues (mine included), but the time to be moved from installer to a well paid tech is too long. As a TV/Appliance tech the electrical stuff comes relatively easy to me, it's the refrigerant stuff I'd have to get field experience with. I could even repair the control boards if it's economically feasible, although if it's like TV/Appliances these days it's more cost effective just to replace the board.

Just going to make a stab at it that you work for Sears/A&E Factory service?