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Working on window AC unit. Capacitor question.

JoeE.

Titanium
Joined
Aug 31, 2006
Location
Kansas
Watched a guy take out a window unit and replace it with a new one. Put old one out at the curb for scrap, so I picked it up.. a challenge to see if I could make it work.

It's a 2003 18,000 btu 220vac Sears. Digital, pushbutton control panel. It was a middle aged lady's, and it was basically clean... no dust in the filter... everything clean.. the condenser face that the fan blows on had some corrosion and the 2 condenser coil/case attachment points were rusted apart..but anyway...

First thing I did was plug it in, push the Cool button and the compressor tried to start, the overload clicked and shut that down... and the fan just hummed.

I pulled it's 35/6 370vac capacitor and replace it with one that wasn't an exact match. I think it was 30/3.5 or something like that.

Turned unit back on... compressor started right up, as well as the fan~ but the fan spun the wrong direction. The fan motor is a 220 volt motor, and was not the reversible type.

The only other cap I had was way larger in numbers (can't remember~ maybe 60/8 or something like that.. but, anyway, both motors started up and the fan ran the right direction with it. I'll go buy a O.E. part replacement when I get a chance. I don't think the machine had ever been taken apart or had any parts changed.

I let the unit run for a while and checked the running amps. I'm not there looking at it right now, but it seems like the data tag said the cooling amps were 9.5... It ran at that figure for about a minute or two... then it climbed up to the 10.5 to 10.7 range, and then I stopped the test run.

It was blowing cold air.. blowing heat out the condenser, but the darn compressor was getting reallly hot, in my estimation.

I know it's not an ideal situation to be testing it in... setting on the tailgate of a truck setting in the 97 degree heat... but the fact that the running amperage was that high and the compressor was so hot makes me question whether something's not right with the refrigerant charge or it was just the wrong conditions to be running the unit and expecting it to function properly?

So, my question: would the "too small" cap cause the fan motor to spin the wrong direction like that?

Not sure if I want to keep this thing or not, but a capacitor is small change to replace in the big scheme of things.. but without putting it in a window in a room and letting it run for a long time to see if it calms down and doesn't catch fire...I don't see any way to verify it's worth keeping.

There are no old school heat and air guys left around here who would take the time to put on some test ports to check the freon charge in this thing, so....
 
The smaller cap on the compressor would cause it to draw increased amps, but much of that amp draw is not "real" and does not reflect the true load on the motor. 60uf would push the motor into saturation and it would also overheat, not just due to the copper losses in the windings.

but it is most likely a rolling piston compressor and the entire shell of the compressor is the high pressure discharge side, it would not supprise me if it will reach 180F on a cheap 18000 btu window ac unit in 97F heat. Running inside at 70F air temp and 97f outdoor temps would be a significanly less loaded state.


Fan running backwards is interesting to me, but those motors are not particularly efficient and as a result can behave strangely with too few or no capacitance
 
I don't know why it's running reverse.
But I've had two window units that stopped working, and I replaced with a new unit. I went to scrap the old units, and found both had extreme dirt on the condenser, that could not be seen without the fan plenum removed. The condensate is by design ran to the outside fan, which has a dipping ring to spray it on the condenser. This will enable air born dust and pollen to glue to that surface.
Are you sure it's not running the right direction? It's intended to push that water spray onto the condenser as it helps remove the heat by the latent heat of fission from the water evaporating.
I suggest you take the screws out holding the condenser assembly with plenum in place and move it away from the fan to see if you have extreme condenser plugged by dirt and lint on the inside surface.
 
Update:
I bought the correct capacitor and the amp numbers got down where they belonged. I let it run for about 10 minutes on the tailgate, admiring my work.

It was rather cold air being produced, but I didn't notice much condensation on the evaporator coil, for as humid as it is.

I reached in and felt the copper tubing bends on the end of the coil, and noticed that the top and bottom thirds of the coil was cold, but the center was not.

For some reason there seemed to be no refrigerant flow through that part of the coil.

Since it wouldn't be worth the time or money to have it worked on.. I just pulled the new cap out, took it back to the hardware store and got a refund and scrapped the unit...
 
Update:
I bought the correct capacitor and the amp numbers got down where they belonged. I let it run for about 10 minutes on the tailgate, admiring my work.

It was rather cold air being produced, but I didn't notice much condensation on the evaporator coil, for as humid as it is.

I reached in and felt the copper tubing bends on the end of the coil, and noticed that the top and bottom thirds of the coil was cold, but the center was not.

For some reason there seemed to be no refrigerant flow through that part of the coil.

Since it wouldn't be worth the time or money to have it worked on.. I just pulled the new cap out, took it back to the hardware store and got a refund and scrapped the unit...


The evaporator has a multicircuit feed. If you looked it has a capillary tube feeding each of the circuits. Most likely wax from the oil has plugged off one of the tubes. The typical fix for that is to heat the tube while it's running with a torch to melt the wax plugging it.
 
Well, crap... I didn't think of that? Wax from the refrigeration oil?

It's too late now.. the unit went bye bye
 








 
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