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Old 08-29-2009, 11:40 PM   #1
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A/C basic questions:


-The temperatures and PSIG are applied to all A/C that ask for R22 even with different tons capacity?


-What is the relationship between the length of the lines and temperatures and PSIG?


-If outside temp is over 95F. How the condense is cooling the liquid?


-If A/C has low Freon, can a tech determine how many lbs is need by just checking the manifold gauge? How can it be done by going by the PSIG?


-How can I find out the temperature for superheat and sub cooling is right? Is it different for each coolant?
Thanks Carlos

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Old 08-30-2009, 11:27 AM   #2
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A/C basic questions:


First,

If you are not trained, CFC certified and/or licensed, DON'T mess with it!
An A/C system is a complicated peice of equipment, even the simple systems involve things that can get a weekend warrior into trouble fast.

To answer the question I think you are asking, no! An A/C technician cannot determine the proper charge by just what he sees on his gauges. He could determine if it is quite low, possibly. However, if he is a good tech, that will only be the first in a series of clues he should be looking for.

IF it is low on refrigerant, then he must determine the cause and then repair the problem BEFORE he can legally introduce any new refrigerant into the system.

You seem to know about sub colling and superheat, so perhaps you do know something about refrigeration, however, that may only be enought to get yourself into trouble. Each unit comes with information as to the approximate parameters that the unit should optimally be running. These are basic guidelines, it is the techs reponsibility to make sure it is running in optimum condition. Some techs and some companies take shortcuts for the sake of getting on down the road to make more money. A consciensous tech and a company that truly cares are not going to do that! DOn't take this the wrong way please, but for your sake and your family's, call someone who cares enough to do right by you!

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Old 08-30-2009, 04:26 PM   #3
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A/C basic questions:


Ok tmboracles, thanks for the reply. I just started my HVAC education. My questions were about what I’m studying and the last A/C repair in my home. You already asked what the tech did. Thanks
I have the “Refrigerating & Air Conditioning Technology 5th Edition as a text book. I understand a typical air-conditioning system temp, pressure and airflow. Let me try to rephrase my question.
If I don’t have any manufacturer parameters that the unit should optimally be running and I know only:
Evap air in temp
Evap air out temp
Low side pressure
Suction line temp

Cond air in temp
Cond air out temp
High side pressure
Liquid line temp


-After calculating the Superheat and/or Sub cooling, how do I know that values are acceptable?
Low charge? Over charge? Etc

How do I know how many lbs I need to add if the system is low charge or remove if the system is over charge?


Last edited by cralx2k; 08-30-2009 at 04:29 PM.
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Old 08-30-2009, 04:51 PM   #4
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A/C basic questions:


By using the sub-cooling for TXV and super-heat for fixed orfice/piston

Low super heat remove freon
High super heat add freon

Low sub cooling add freon
High sub cooling remove freon
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Old 08-30-2009, 04:54 PM   #5
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A/C basic questions:


most manufactures will list the super heat / subcooling on the cond. unit or paper work
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Old 08-30-2009, 05:01 PM   #6
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A/C basic questions:


Hey Ken.

But when the sticker fades on the condenser I use 10deg for piston and 13 for txv.


I also compare the two and most the time they are pretty close to each other unless there is a huge heat load inside the house. Sometimes on a HOT day I will start the system up and let it run 24 hrs and then go back the next day and do final adjustments.
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Old 08-30-2009, 05:19 PM   #7
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A/C basic questions:


Quote:
Originally Posted by Plumber101 View Post
By using the sub-cooling for TXV and super-heat for fixed orfice/piston

Low super heat remove freon
High super heat add freon

Low sub cooling add freon
High sub cooling remove freon

Add/remove freon by looking manifold gauge and recalculating the SH and SC? or add/remove freon in pounds? I don't get when people say that the unit need ex: 4lb

Thanks for the help.
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Old 08-30-2009, 05:24 PM   #8
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Quote:
Originally Posted by kenmac View Post
most manufactures will list the super heat / subcooling on the cond. unit or paper work
Without technical information from the manufacturer or without the label on the back of the condenser I'll have to guess a value?

Thanks for the reply.
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Old 08-30-2009, 05:27 PM   #9
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A/C basic questions:


Add/remove freon and then recalculate..YES

There is no way to look at a set of gauges and tell how much freon to add or remove other than adding/removing freon wait 5-10 mins and recalculate.

If anyone tells you they can look at a set of gauges and tell the exact amount of freon to add/remove without allowing the system to stablize and recalculate is full of it.
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Old 08-30-2009, 05:46 PM   #10
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A/C basic questions:


Quote:
Originally Posted by Plumber101 View Post
Add/remove freon and then recalculate..YES

There is no way to look at a set of gauges and tell how much freon to add or remove other than adding/removing freon wait 5-10 mins and recalculate.

If anyone tells you they can look at a set of gauges and tell the exact amount of freon to add/remove without allowing the system to stablize and recalculate is full of it.
Okay, this already happened in my house before. The "tech" told me that the unit was low freon. He added freon by looking the set of gauges and at the end He said we need 4lb LOL. Now I know the right way should be. Thanks
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Old 08-30-2009, 07:08 PM   #11
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A/C basic questions:


You only starting your A/C edcation?

Is this to get into the trade.
Or just to work on your own A/C
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Old 08-30-2009, 08:37 PM   #12
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Quote:
Originally Posted by beenthere View Post
You only starting your A/C edcation?

Is this to get into the trade.
Or just to work on your own A/C
I want to get into the trade. Iím taking online classes at Penn Foster. After I finish the class, Iíll take the EPA and Nate certifications. I already started to get my HVAC tools. I work in the IT industry but to be honest, I think most of our jobs will be outsourced overseas. I really appreciated your feedback in any tips to get into the trade in the future.
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Old 08-30-2009, 08:57 PM   #13
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A/C basic questions:


You should join the pro only site.

There is a;ready misinformation posted in this thread.

Even at 135 degrees you can condense a vapor, by increasing its saturated pressure above the temp of the outdoor air. As long as the outdoor air temp is not at, near, or above the refrigerants critical temp.
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Old 08-30-2009, 09:18 PM   #14
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A/C basic questions:


Quote:
Originally Posted by beenthere View Post
You should join the pro only site.

There is a;ready misinformation posted in this thread.

Even at 135 degrees you can condense a vapor, by increasing its saturated pressure above the temp of the outdoor air. As long as the outdoor air temp is not at, near, or above the refrigerants critical temp.
I was banned there. http://www.hvacsite.com/f7/xe-1100-outside-unit-179/

I'm still try to find out what I did wrong.
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Old 08-30-2009, 09:34 PM   #15
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A/C basic questions:


Your post came across there as a DIY question which is not allowed there. Contact Nathan the administrator at the far bottom right of that page (contact us) and explain who you are (student) and what happened and he may let you in. It is a good site and I can give you some more info and so can other pro's. Make SURE you let the members know you are a student so they don't think you are a DIYer there. Charging A/Cs is not an exact science. Airflow thru the evap coil, cleanliness of the evap and condensor coil, mismatched coils and lines etc can affect the system charge. Some of it you have to learn from experience in the field but you are on the right path.

Good Luck

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Last edited by yuri; 08-30-2009 at 09:41 PM.
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