The slim units are notoriously expensive to repair and the indoor unit should not be more than 25 feet from the outdoor unit so as not to burn out the compressor. They are more efficient than an in-window unit but start out at 12,000 btu and above - so they require more power overall.
My suggestion to the cheapest solution would be to ventilate the closet in the back of your rack with a ceiling exhaust fan and run the exhaust air via a round duct outdoors. The heat build up from your equipment rack is contributing to the load that your present a/c system cannot handle. By exhausting the air from the closet, you reduce the air temp back to the a/c unit since the make up air is taken from the conditioned space inside the house.
Broan (www.broan.com) makes a "LoSone" fan that is dead quiet. I would use a 200 to 300 cfm fan in the closet ceiling with an 8-inch flex round to a wall jack outside the house. If you can spend a little more, wire the fan with a dedicated circuit to minimize electrical noise.
This is the way telephone/network server closets in buildings are ventilated; it seems you have a similar heat load.
My suggestion to the cheapest solution would be to ventilate the closet in the back of your rack with a ceiling exhaust fan and run the exhaust air via a round duct outdoors. The heat build up from your equipment rack is contributing to the load that your present a/c system cannot handle. By exhausting the air from the closet, you reduce the air temp back to the a/c unit since the make up air is taken from the conditioned space inside the house.
Broan (www.broan.com) makes a "LoSone" fan that is dead quiet. I would use a 200 to 300 cfm fan in the closet ceiling with an 8-inch flex round to a wall jack outside the house. If you can spend a little more, wire the fan with a dedicated circuit to minimize electrical noise.
This is the way telephone/network server closets in buildings are ventilated; it seems you have a similar heat load.