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-   -   a/c question (http://www.diychatroom.com/f17/c-question-179791/)

markharmon 05-17-2013 09:35 AM

a/c question
 
Hi,

Sorry if this is a dumb question but are there any central a/c units you can buy that are pre-charged?

NitroNate 05-17-2013 10:23 AM

i'm pretty sure every condenser is pre-charged with a certain amount of refrigerant from the factory based on an assumed line length. you will typically need to add or remove some charge depending on the length of your lines as every setup is different.

Marty S. 05-17-2013 11:10 AM

Systems with 410A come with enough for x coil and 15 ft of lines . Charge will need to be adjusted when using y or z coil. R22 units will not come with refrigerant.

bobinphx 05-17-2013 11:20 AM

I am not trying to be flip... but package units are pre-charged.

markharmon 05-17-2013 06:25 PM

Quote:

Originally Posted by Marty S. (Post 1181168)
Systems with 410A come with enough for x coil and 15 ft of lines . Charge will need to be adjusted when using y or z coil. R22 units will not come with refrigerant.

If I purchase a system online is it feasible that I could install it myself?

Marty S. 05-17-2013 07:08 PM

Quote:

Originally Posted by markharmon (Post 1181445)
If I purchase a system online is it feasible that I could install it myself?

It's possible. Price some of the tools you'll need like oxy/ace torch set,dry nitrogen tank and regulator,Lb of 15% silphos(they don't sell smaller amounts),micron gauge,manifold set and vacuum pump before going too far though. It might be cheaper to hire the hook up and set up.

markharmon 05-17-2013 09:44 PM

Quote:

Originally Posted by Marty S. (Post 1181479)
It's possible. Price some of the tools you'll need like oxy/ace torch set,dry nitrogen tank and regulator,Lb of 15% silphos(they don't sell smaller amounts),micron gauge,manifold set and vacuum pump before going too far though. It might be cheaper to hire the hook up and set up.

Don't these come precharged? I understand I need to braze the lines but why the other stuff if its already charged?

JScotty 05-17-2013 09:58 PM

Quote:

Originally Posted by markharmon (Post 1181624)
Don't these come precharged? I understand I need to braze the lines but why the other stuff if its already charged?

It has freon in it, but that doesn't mean your unit will be properly charged. One unit may have a 10' lineset connecting to the indoor coil another unit may have 100' lineset. The freon will need to be adjusted depending on the lineset length.

Also you HAVE to vacuum the unit which can't be done without a vacuum pump, guage manifold and you might want a micron guage as well. (although you can do it without it) Failure to properly vacuum the system will cause the compressor to fail very quicky (I've seen them go out in a couple months when not vacuumed)

By the time you buy a torch set, tanks of oxygen & acetylene, brazing rods (you can't use plumbing solder) gauges & a vacuum pump you're going to be in for a lot of money. It may just be better to have someone else do it that way you know the unit will be properly installed & charged

hvac instructor 05-17-2013 11:17 PM

he might be thinking of when you were able to buy a
precharged line set and evap and condensing unit.

gregzoll 05-18-2013 12:15 AM

Quote:

Originally Posted by Marty S. (Post 1181168)
Systems with 410A come with enough for x coil and 15 ft of lines . Charge will need to be adjusted when using y or z coil. R22 units will not come with refrigerant.

You can still find some precharged r-22 units that are not "dry-charged". They are just hard to find, unless you know who to contact to get one. Any others are going to be "dry-charged" from reputable places.

beenthere 05-18-2013 04:11 AM

You can buy and install the unit yourself. And then use an HVAC company/service tech to vacuum and check/adjust charge.

Marty S. 05-18-2013 08:25 AM

Just the condensing unit has refrigerant Mark,assuming we're talking about a split system and not a package unit. The line sets will have air in them and the evap coil has some nitrogen to keep a positive pressure on it in storage. Once the caps are removed from the lines and the plugs taken out of the evap coil then moisture that's in the air moves in. All that has to be vacuumed out with the pump before opening the valves on the condenser( which releases the charge into the system). Every brand that I have installed required either a 250 or 500 micron vacuum,you can't see that level of accuracy without a micron gauge.

Dry nitrogen serves two primary purposes. First it keeps oxides from forming inside the copper lines while brazing. A slight flow through the copper while heated will keep the oxygen out so no oxides. Secondly it's used to pressure test the joints,usually fill to 150-200 psi. On the rare occasion that the micron gauge shows the system is having a hard time pulling down to the required vacuum because the air was really moisture laden then multiple vacuums are done,breaking all but the last with a shot of dry nitrogen.

yuri 05-18-2013 08:37 AM

As a side note for all the techs and you all probably know but here it is anyway:

Best way to decrease the time to pull a 500 micron vacuum is to replace the oil in your vacuum pump regularly. It gets loaded with moisture. I can pull a 500 micron vacuum on a new (unused) lineset in 5 minutes with clean oil and a 2 stage pump. Dirty oil and it takes 4ever.

markharmon 05-18-2013 10:05 AM

Quote:

Originally Posted by Marty S. (Post 1181797)
Just the condensing unit has refrigerant Mark,assuming we're talking about a split system and not a package unit. The line sets will have air in them and the evap coil has some nitrogen to keep a positive pressure on it in storage. Once the caps are removed from the lines and the plugs taken out of the evap coil then moisture that's in the air moves in. All that has to be vacuumed out with the pump before opening the valves on the condenser( which releases the charge into the system). Every brand that I have installed required either a 250 or 500 micron vacuum,you can't see that level of accuracy without a micron gauge.

Dry nitrogen serves two primary purposes. First it keeps oxides from forming inside the copper lines while brazing. A slight flow through the copper while heated will keep the oxygen out so no oxides. Secondly it's used to pressure test the joints,usually fill to 150-200 psi. On the rare occasion that the micron gauge shows the system is having a hard time pulling down to the required vacuum because the air was really moisture laden then multiple vacuums are done,breaking all but the last with a shot of dry nitrogen.

Hi and low side gauges get connected to the corresponding ports on the condensor then the utility port on the gauge to the vacuum? You should wait till it reads 0 psi and your good? Is this correct?

markharmon 05-18-2013 10:38 AM

Quote:

Originally Posted by yuri (Post 1181801)
As a side note for all the techs and you all probably know but here it is anyway:

Best way to decrease the time to pull a 500 micron vacuum is to replace the oil in your vacuum pump regularly. It gets loaded with moisture. I can pull a 500 micron vacuum on a new (unused) lineset in 5 minutes with clean oil and a 2 stage pump. Dirty oil and it takes 4ever.

When the term "draw" is used in HVAC. What does that mean exactly? Also, I get confused by what the purpose of a draft hood is. Can someone please explain to me. Thank you.


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