dead Friedrich AC unit, Model KM18J30B-3

[paulcats02]

Unit is a Friedrich Quietmaster Model KM18J30B-3. It doesn't turn on (doesn't work in "cool" or "fan only" modes). I have measured voltage at the outlet I am plugging into to make sure that is not the problem and there is 110V there. I opened up the unit and tested the switch, it appears to be fine (switched "off, I measure no continuity where in any of the "on" position, I have continuity). There is a big metal dual AmRad Ultramet capacitor that looks to be for the compressor and fan, I could measure the capacitance on that but am not sure what #'s to look for. On the cap it says 30.0/7.5V, I'm guessing that the former is for the compressor and the latter for the fan. Thanks.

[paulcats02]

thats MF microfarads not volts, as jkirksey1889, pointed out.

attached is image of capacitor

[paulcats02]

here is 2nd image of the cap... and i'm thinking to get the multimeter out, fired up and get testing

[paulcats02]

measured about 6-12nanoFarad between the test point(s) and common when it should be 30 and 7.5MicroFarad; basically nothing. it's about a $15 part but i'm not a big fan of shotgunning it so maybe i'll double check continuity on the switch to make sure that's not the prob...

[ACtechGUY]

Replace the capacitor. It is dead . they go bad quite often. expect to replace the new one in a few years as well.

A very easy indicator that a capacitor is bad is a bulging top. it should be totally flat. if it isn't it is bad.

[paulcats02]

actually i bought a replacement capacitor which i measured the capacitance of (right out of the box); it measured fine as expected:bananadance:.

prior to replacing the "suspect", for grins and giggles i measured it... lo and behold, it measured fine; when i measured it previously i had only removed the wires from the common terminal and left the wires on the fan and herm terminals so maybe that threw off the measurement? :?

so, at this stage of the game, i guess i need to look at the schematics and recheck the switch (maybe it's bad after all though it seems to test fine) as well as measure voltage at various points to see where it's dropping off.

 :nerd:

what's throwing me off is that neither the fan nor the AC work, that's why I was suspcious  that there was a commonality that was/is the culprit but i just don't know which way to go...

[appl.tech.29501]

bypass the cold control (thermostat) by tying the 2 wires together and see if the compressor comes on when the units is turned to cool. you may have more than one problem or you may have a bad selector switch.

[paulcats02]

>bypass the cold control (thermostat) by tying the 2 wires together and see if the >compressor comes on when the units is turned to cool. you may have more than one >problem or you may have a bad selector switch.

thanks for the reply by the way. was away for a while and now we're back it's hotter than heck here in NYC. what 2 wires am i to tye together, i have an alligator clip to alligator clip cable ready to go...?

regards

p

[appl.tech.29501]

I dont have a diagram for this unit. How many wires do you have attached to the temperature control switch?

[paulcats02]

>dont have a diagram for this unit. How many wires do you have attached to the >temperature control switch

 

thanks for the post

 

i've got four wires attached to the temperature control switch

 

the thermostat sensor has 2 wires (one goes to the temperature control switch and the other to the control switch) 

[RegUS_PatOff]

 

similar model wiring diagram

[paulcats02]

great, thanks!

now i believe i am close to cooking with gas... or cooling with gas but not quite yet.

it looks like what i am calling the "thermostat sensor" is actually known as the "anticipator resistor" on this schematic; it looks like that is wired to to the system switch and the thermostat (temperature control). the thermostat is also wired to the compressor via the compressor wire harness and the system switch.

so maybe i need to tie those 2 wires together (the last 2 mentioned above)?

 

 

[RegUS_PatOff]

[user=51113]paulcats02[/user] wrote:

... (doesn't work in "cool" or "fan only" modes) ...

would seem to be a problem with the System Switch

[appl.tech.29501]

Jump Line voltage Black to black, blue, or red on system switch and see if the fan comes on... (based on diagram above)

[paulcats02]

tried your suggestions for jumping the wires, appl.tech, and nothing happened... no fan.

since that effectively takes the switch out of the equation, my guess is that the switch is not defective as RegUS PatOff suggested.

looking at the schematic it looks like i have a bad compressor; not sure what else there could be that would fail since i have ruled out the breaker, power outlet, capacitor, the switch, and the thermostat.

not sure how exactly to confirm that, and if i could is it a readily available part, how much does it cost, do i need to take the unit out of the window to replace, etc...

:violin: 

[RegUS_PatOff]

If the Compressor was bad, the Fan should still work

check the voltage at the 2-position Fan/Rocker Switch

center Terminal (Brown) to chassis (a good ground)

Test the voltage with the Switch in each position

 

If no voltage:

test for voltage at each of the outer 2 terminals

Grey to chassis (a good ground)

Purple to chassis (a good ground)

[paulcats02]

thanks for the reply.

not sure if i understand though.

the fan is on a 5 position "Mode" switch (lo cool, med cool, hi cool, fan only, and off). then there is a 2 position rocker switch but that is for the "Moneysaver" feature (yes/no).

hey if it is just a bad switch i'd be happy as a pig in a sty but i still need to proof it out...

[RegUS_PatOff]

[user=3641]RegUS_PatOff[/user] wrote:

... check the voltage at the 2-position Fan/Rocker Switch

[Bobice]

[user=51113]paulcats02[/user] wrote:

thanks for the reply.

not sure if i understand though.

the fan is on a 5 position "Mode" switch (lo cool, med cool, hi cool, fan only, and off). then there is a 2 position rocker switch but that is for the "Moneysaver" feature (yes/no).

hey if it is just a bad switch i'd be happy as a pig in a sty but i still need to proof it out...

The purpose of the "money Saver" switch is when it is on it will cycle the fan (shutting it off) with the compressor.

Therefore you may have two problems.

1. Bad selector switch

2. Bad "Money Saver" switch.

Unfortunately the computer here at the health care facility I am in will not allow me to open the diagram. (Adobe blocked)

[paulcats02]

sounds like i need to test these switches again!

[RegUS_PatOff]

[user=3641]RegUS_PatOff[/user] wrote:

If the Compressor was bad, the Fan should still work

check the voltage at the 2-position Fan/Rocker Switch

center Terminal (Brown) to chassis (a good ground)

Test the voltage with the Switch in each position

 

If no voltage:

test for voltage at each of the outer 2 terminals

Grey to chassis (a good ground)

Purple to chassis (a good ground)