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Old 05-19-19, 12:41 AM   #2
jeff5may
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That's a 2 ton 10 seer unit. Not super efficient by today's standards. Not much better than a window AC unit. But, I'm assuming it was donated or a super bargain. I myself would add a reversing valve, a txv, and a defrost control and turn it into a heat pump for a couple bucks and a couple hours work, but that's me.

Before you start, look at a few other threads where others have been down this road. You will need some tools and equipment, and a few instruments to get it done. Start gathering tools and practice some methods on scrap if you aren't confident.

First thing you want to do is purge the plumbing. Make sure the cut lines are not full of bugs or other crap. If so, use some pipe cleaners or qtips and brake parts cleaner to get the funk out. If you suspect the unit is contaminated with moisture or dust or rust, you can get some "burnout cure" purging juice/system cleaner from your favorite local auto parts store or HVAC supply house. Pour some into the suction line, then blow it through with compressed air. Repeat a few times. Rinse with alcohol or brake parts cleaner.

Once the lines are clean, you can go at purging a few different ways. With ozone depleting and global warming gases, you should reclaim. With hydrocarbon gas, not necessary. Just don't make a fireball if you vent to atmosphere. The pros use compressed dry nitrogen.

Seal up the lines, pressurize the unit to somewhere near design pressure, and let it sit for a bit to verify that you don't have any leaks. If the pressure holds, then you can vent the charge and pull a vacuum. If not, find your leaks and eliminate them. If you don't have a vacuum pump, and don't want to buy one, the flaps rents them out for cheap or free on the loan a tool program. You'll need a refrigeration gauge and lineset and a micron vacuum gauge. Charge, purge, charge, purge, vacuum, charge, purge vacuum. Last charge, only put in like 10 or 15 psi.

Now you can connect the copper lineset and indoor unit with confidence that it won't be contaminated by the outdoor unit. Again purge, pressurize and do leak check. Most pros pull 2 deep vacuums on used systems to make sure that it is clean and void of moisture. Last charge, switch to the refrigerant gas. If you're going to use a filter dryer, put it in after pulling at least one deep vacuum on the whole system. Break the vacuum with purge gas, pressurize to like 5 psi, breach the liquid line and quickly install the filter. Pressurize, leak check, purge, pull vacuum. Lower micron reading is better.
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