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-   -   A/C charging question (http://www.diychatroom.com/f17/c-charging-question-179904/)

markharmon 05-18-2013 07:56 PM

A/C charging question
 
Hi,

I just wanted to check my a/c unit to make sure there is the proper amount of refrigerant. What methods can I use to check that?

joecaption 05-18-2013 08:05 PM

Pick up phone, call HVAC company.

ben's plumbing 05-18-2013 08:38 PM

Quote:

Originally Posted by markharmon (Post 1182092)
Hi,

I just wanted to check my a/c unit to make sure there is the proper amount of refrigerant. What methods can I use to check that?

hooking up a set of gauges see whats going on...ben sr

bobelectric 05-18-2013 09:15 PM

If you aren't certified,the homeowner metheod would be to use a thermometer to check air temperature at registers. Look for temps between 50 and 55.

markharmon 05-18-2013 09:17 PM

Quote:

Originally Posted by ben's plumbing (Post 1182117)
hooking up a set of gauges see whats going on...ben sr

Hi Ben,

How do I know what pressure my system should be at after hooking up hi and low side gauges?

Ebierley 05-18-2013 09:22 PM

You can't check charge based on pressures alone. You need indoor wet bulb temps, super heat and sub cool, and required super heat and sub cool requirements. Also, you need to be EPA 608 certified to connect gauges to residential AC systems.:whistling2:

Marty S. 05-18-2013 09:35 PM

Be a whole lot easier for you to post the data than for us to go through all the steps and formulas.
Outside air temp
Indoor return wet bulb and dry bulb temps
Supply wet bulb and dry bulb temps
measured cfm
suction line temp
liquid line temp
make and model of AC
type of metering,txv or fixed orifice

beenthere 05-18-2013 10:06 PM

Super heat and sub cooling are used to determine if the unit is charged correctly and operating properly.

markharmon 05-18-2013 10:58 PM

Quote:

Originally Posted by beenthere (Post 1182160)
Super heat and sub cooling are used to determine if the unit is charged correctly and operating properly.

Right so why are the other members asking for wet bulb temp, dry bulb temp, return air temp, etc.? How do I find out what pressure my system should be operating at?

beenthere 05-19-2013 05:37 AM

Quote:

Originally Posted by markharmon (Post 1182194)
Right so why are the other members asking for wet bulb temp, dry bulb temp, return air temp, etc.? How do I find out what pressure my system should be operating at?

Indoor wetbulb(best taken at the indoor coil) is used to determine what the super heat should be.

There is no "the system should be at this pressure" answer.

At 86 degrees outdoor temp and an indoor wetbulb temp of 63 degrees, a fixed metering device system has a target super heat of 11 degrees.

At 86 degrees outdoor temp and an indoor wetbulb temp of 67 degrees, a fixed metering device system has a target super heat of 17 degrees.

At 86 degrees outdoor temp and an indoor wetbulb temp of 71 degrees, a fixed metering device system has a target super heat of 23 degrees.

The saturation pressure/temp of the suction must of course be above 32F, so the evap coil doesn't freeze.

ben's plumbing 05-19-2013 07:30 AM

then check super heat and sub cool to see if you have the proper charge on system based on reading.....ben sr

ben's plumbing 05-19-2013 07:34 AM

Quote:

Originally Posted by markharmon (Post 1182194)
Right so why are the other members asking for wet bulb temp, dry bulb temp, return air temp, etc.? How do I find out what pressure my system should be operating at?

all these steps are relative to checking a/c systems.....some techs go a different way to arrive at a point where this system is either properly charged or under charged..ben sr

markharmon 05-19-2013 09:24 AM

Quote:

Originally Posted by ben's plumbing (Post 1182290)
then check super heat and sub cool to see if you have the proper charge on system based on reading.....ben sr

If I get a set of gauges how do I know what the system pressure should be at?

Ebierley 05-19-2013 09:43 AM

Quote:

Originally Posted by markharmon (Post 1182331)
If I get a set of gauges how do I know what the system pressure should be at?

What everyone is trying to tell you, there is not a pressure it should be. The correct pressure depends on all the readings we are telling you. Depending on load on the system the pressure changes constantly. What is the correct pressure today is the incorrect one tomorrow. A real tech does not check charge by pressure alone. With the cost of gauges, EPA card, thermometers etc. it would be cheaper to find a good tech.

Why are you concerned with the charge? Did it not perform well last year? The charge will be the same unless the system has a leak.

COLDIRON 05-19-2013 09:58 AM

The very first thing to know is what type of refrigerant is in the equipment. The next thing to know is what pressures they operate at. The next thing is to buy a set of gages compatible with the type of refrigerant your using. You should also have a set of superheat thermometers, a digital temperature analyzer with 2 leads to check 2 temperatures at the same time. Then you will need a jug of refrigerant the type that's in the unit. Next you might need a scale to weigh in th refrigerant. Now after all that you really shouldn't be putting gages on a unit to check the freon unless you really have done many checks before that. The reason, every time someone puts gages on a unit it losses a couple Oz's of freon which has to be calculated back in to the unit.
Probably should call a pro. Call me now or call me later it'll cost you more later when you F--- everything up.


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