Cheap Central Air Conditioning

[daveshoe]

How does $350 plus a day of work sound? I have a rental unit with a 30 year old furnace[read huge in size]. The cold air return plenum had enough room to install a 17000 BTU window unit into it . I merely cut the cold air return and installed the room side of the unit into the plenum. i also fabricated a primitive air scoop in front of the unit so it can draw relatively still air across the coil. Without the air scoop, the unit would short cycle and not do it's job, but with it , the compressor is running continuously. The thermostat has a range of 66 to 75 degrees, so I need to find the right setting for it

Just powered it up this afternoon and I will return tomorrow to see how it is working. It exhausts into a cool basement,but it would not be difficult at all to use a duct system to exhaust the hot air to the outside. I expected problems with noise and such with a telegraph effect thru the ductwork, but that is not even noticeable.

Wish me luck

 

[The patriot]

NICE!!!

Mine cost me $3000 last year.

Window units were annoying, had to get rid of them.

Eric

 

[HoleshotHolset]

Cool! (pun intended)

That sounds like something I would try...



I bet you even got to use some duct tape on this project! :-laf



Matt

 

[TORQUE THIS]

I remember seeing a pic of a pick-up with a 5000 BTU mounted in the rear window... Can't find it now...

 

[daveshoe]

Problems develop

I need to do some more work on this thing. The window unit is in the plenum with air rushing past it and my efforts to create a dead air zone have not worked yet. I tried a new way to block the air today, but I think the furnace fan speed[air handler] needs to be decreased. I have purchased a smaller pulley to change the fan speed. The trick will be to have just enough speed to distribute the air without allowing the unit to cycle on and off too much.

The unit is easy to experiment with as it sits on a shelf supported by the main furnace frame. It is easy to slide in and out for filter cleaning and adjustment. The downside to this system is the fact that there is no thermostat in the conditioned space--just an on--off switch and the circulating switch will be a double throw to place the fan in constant on for the air cond. and furnace mode for winter.

If this all works out, i'll post more details on how the problems were solved.

 

[Skydiver]

Dave,

Is the outside (rear) of the A/C able to get enough fresh air from the great outdoors?

I ran up on someone doing this same thing last week.

My trade school instructor once told me "Son a refrigeration unit does not cool,it transfers heat. "

Tim

 

[daveshoe]

Originally posted by Skydiver

Dave,

Is the outside (rear) of the A/C able to get enough fresh air from the great outdoors?

I ran up on someone doing this same thing last week.

My trade school instructor once told me "Son a refrigeration unit does not cool,it transfers heat. "

Tim

The project is not that far along yet. I am planning to make an exhaust plenum that will force the exhaust to the outside if the basement that it exhausts into now gets overheated--it should if the unit operates like I hope. I need to get a smaller furnace fan motor drive pulley as I think the problem is that there is so much suction/turbulence by the AC unit that the cold air is not coming out of the unit. Sort of like running the air flow backwards thru the unit.

 

[daveshoe]

Update

Since the function of the air conditioner was OK and was pumping heat out of the condenser,I just could not figure why the COLD was not coming out of the ductwork. I started checking all the return lines coming into the ductwork and it turns out that there was one open to the basement and four others open to the second apartment. I buttoned them up and am seeing a one to two degree drop in air temps in the ducts versus the room air temps.

When I left the apartment ,Temp was 72 and you could feel that the air was less humid. The unit is set at 66 degrees, and if it cools to 70, I will consider this a success. If I have time, I will force vent the waste heat to the outside as it would surely help a little.

 

[Peter Campbell]

The unit will also discharge its moisture out of the condensing side. This will make the basement more humid, and could cause a mold/rot problem. Central air units take the water from the "A" coil ( evaporator ) and pump it to drain or outside to the condensing unit.

 

[daveshoe]

Thanks, Peter

My previous post described what I thought was going to be a success. After letting the unit run all night ,nothing much happened. The way I see things now is that there are three air streams to manage. Stream 1 is the ''room''air going into the air conditioner. This air needs to come from a duct coming from the conditioned space. Stream 2 is the output of the air conditioner. this will be pulled into the furnace return side under vacuum from the furnace blower. I probably need to put an adjustable damper in this line to regulate the flow so as to duplicate what the window unit puts out in its normal usage. Stream 3 is condenser side which needs to be ducted outside. I will take some care with this as condensing water vapor will have to be controlled.

My failure so far is that stream 1 and 2 were both in the ductwork and in turbulent air. Results were reduced output .

If I cannot get this to work soon ,I guess I will just use the thing as a window unit and connect the furnace fan to come on when the unit is used to even out the temps. ----------OR put the beast in the Dodge Garage. 17000 BTU's would make changing the oil an easy job

 

[daveshoe]

Busted out

Do not try this at home! Common sense says it should work , but it does not. After many attempts to isolate the incoming from outgoing air flow, everything should have worked, but did not. Just mounting the unit in a bedroom and using the furnace fan to circulate the air worked much better.

Sometimes the best education is learning the hard way

 

[HoleshotHolset]

I would have thought that this could work - you even did things 'right'...



Oh well - at least you learned some new things.



Matt