Advice on A/C?

[Fred Conte]

I want to put central a/c in my shop and there are several used units for sale locally. I estimated that I would need a 3 ton unit for my 24x60 shop, 24x48 enclosed.

My question is how would you check the unit before purchasing? Essentially, what should I look at/for, how would I inspect it? I know very little about these large units. What tools should I bring - a/c gauges, ohm/volt meter, etc?

Thanks for your assistance and advice!

Fred

[Frank Guerin]

Fred. I hope you get some responses because I really have nothing of value to add. A few years ago I was searching for something simular and only one was on line so for the rest the only thing I beleive you could check is for continuity and that nots much.
Buying used AC not on line is in my opinion not a good bet because of possible compressor problems but at the same time the price should be at the very bottom. Freon is a given to be replaced and electrical is not a killer with a little shopping but you may wish to check on the compressor replacement.
Hope you find a good deal. I,m sure they are there and if your like me too afraid to take the chance.

[Tom Godley]

The only way I would ever reinstall a used unit is if it was removed working and I knew how old it was how it was used and that the condenser and evaporator matched.

Many years ago my oil furnace died, I decided to switch the house over to natural gas and to also replace the a/c unit. The a/c unit was about five years old at the time -- I put it into a rental unit that was getting a new heater.

I was advised against this by my A/C guy for a few reasons - but we went ahead and it actually worked fine for over fifteen more years.

There have been many improvements in the efficiency of A/C units in the last few years. You are in Florida -- any used unit will have had a tougher life than the one I had in NJ -- plus you will have to pay to run a much less efficient unit.

The cost to install the units will be about the same -- if you can get a new unit at a good price that uses 410 vs R12 the cost will be even less because R12 is getting very $$.

I know you can buy Goodman units online as kits -- You would be better of with a simple new unit than taking the chance on an old one. Goodman sometimes get a bad rap because they can be purchased without going through a distributor and are therefore some are not installed by qualified A/C people.

Go to hvac-talk.com -- you will get a lot of help on this.

No matter what the charging is not a DIYS.

[Fred Conte]

Thanks for everyone's input!

I've been having a similar discussion on the shopfloortalk forum. And have decided to stay away from used units.

I've decided to go with three new window units: 6.5K in my machine shop(12x12), 8K in my hobby area (12x24) and 12K btu in my woodshop area(24x24). I'll loose 3 of my 4 windows but I rather be able to use my shop then sit in the house because of the heat and humidity.

Lowe's is having a sale on Frigidaire units which I like some of the features: 10.8 efficiency, all are 120 VAC, 24 hr timer, brownout protection just to name a few.

I attached a simple floor plan so you will see the layout.

BasicLayout.jpg

The woodshop area has 14' ceilings and the hobby, machine/garage area have 8' ceilings with lofts above that open into the woodshop area.

HTH - Fred

[Rob Russell]

If you're going with window units, I'd put a furnace filter over the intake on the one in the workshop to help capture shop dust before it clogs up the AC. That will slow down the airflow and effective cooling capacity of the AC unit.

A benefit to your approach is that you can cool just the area you'll be working in.

[Fred Conte]

If you're going with window units, I'd put a furnace filter over the intake on the one in the workshop to help capture shop dust before it clogs up the AC.

I do have a CV system but dust still gets in the air!

Excellent suggestion Rob, I will do that - thank you!

[Rob Russell]

I do have a CV system but dust still gets in the air!

If "dust still gets in the air", I would suggest upgrading your DC system. Long term exposure to fine wood dust isn't a good thing.

If you have a CV - Central Vac - system, I'd rather see you put your $$$ into your lungs than AC.

[Fred Conte]

When I said CV (central vac) I meant a dust collection system, I always use the terms interchangeably.

No matter how good your CV/DC system is a small amount of dust will still get into the air. I wear a Trend Airshield when doing alot of cutting, turning, sanding, etc. I also have a dust filter system that I made using a discarded squirrel cage from a HVAC system which works really well.

I agree lungs are more important thanks for your concern!

Fred