Brisk Air conditioner not running HELP

[borgy]

I have a truck camper that has a brisk air unit and when I turn it on all I get is a very slight hum. work nothing comes on, no compressor or fans work. Anyone have any fix or may no the related problem? Thanks, Tim

[j-d]

ScottG wrote:

A blown cap doesn't have to look like the images I provided but if it does look like them it's bad.

If you can provide a pic of the caps, I may be able to tell you if it's blown for sure.

Scott

Absolutely! Some caps have a little blowout plug that'll show electrolyte when they fail.

I carry a spare for the RV A/C. Compressor was running hot (cycled out and had to cool) and didn't sound right. Decided to swap the spare in and the thing sounded right again, didn't cycle out. Fluke DVOM with Capacitance said the original was OK. This confirms what Scott is saying, just replace after awhile.

I'd have to go back and try to research, unless somebody here knows this cold: There's an "hours" rating as well as the uF and VAC spec for capacitors. I was paying twice at one appliance parts shop, for caps that weren't rated to last as long as the less expensive ones at another shop.

[ScottG]

OK, to clarify...
A blown cap doesn't have to look like the images I provided but if it does look like them it's bad.

Also, I would never replace an AC because of a simple failed cap, which is a normal failure. In fact, in home AC systems the caps are a maint. item that should be replaced periodically. Probably should be done in RV units as well.
BTW, How old is the AC unit?

If you can provide a pic of the caps, I may be able to tell you if it's blown for sure.

If you want, I can PM you my Ph# so you can send me a text/pic.

Scott

[j-d]

A failed capacitor doesn't have to be bloated like the pix in the link. Can look great and just not work. The pic following is a RUN Capacitor. It is actually two capacitors in one, serving both Compressor and Fan. It'll be labeled with two values in MicroFarads, such as 40 MFD and 5 MFD for Compressor and Fan respectively You can tell it serves both because it has a total of three terminals. One is Compressor (may be marked HERM), the other is Fan, third is common to the other two.
The plastic one is a Start Capacitor, serving only the Compressor and should look about like this.
Some meters will measure Capacitance and give a pretty good idea if a capacitor is good or bad. Many techs will simply substitute a new or known good one.
Does this A/C use a Wall Thermostat, or does it have just a couple control knobs? I ask because I'm not familiar with the control boxes that go with wall thermostats. A bad part in the control box could be doing nothing but make a hum, not even trying to run the A/C itself.
If it's knob type, like ours, I'd suspect that dual capacitor had failed in a way that killed both Compressor AND Fan. What are the two MFD (might be expressed as uF) values, and the AC Voltage, marked on it?
Another test you might try, is find a clamp-on Ammeter. Amprobe is the name brand. Measure the current draw by clamping over a power wire to Fan, then to Compressor, when you are trying to start the system. Best to have somebody on top with the meter, helper to turn system On and Off. Don't leave it straining to start (showing AMPS) very long. If the Capacitor is bad, AMPS will exceed the spec on the labels of Fan and Compressor. Sure, they could both be seized, but you can eliminate that for Fan if it spins.
Just for me, if an A/C has refrigerant leaks or bad compressor, it's junk. If it needs Controls, Fan Motor, Capacitors, etc. then it's repairable.

[time2roll]

How old is this unit? I honestly think you are looking at a new one.

[ScottG]

Yes! Look at the caps where the wires connections are. Often when the cap has failed, there is physical damage to it. It may even puke its guts out!
Here is a link to what some types look like when they let go or are about to.
If the end that has the connections isn't flat, it's probably bad.
Some also have a little rubber plug in a hole. That's a vent and stuff will blow out of it at death.

If you could post a pic, we could probably tell you if they've failed.

[borgy]

Tried that on top andvtge fan was a bit tight but freed right up quickly, I thought I had it but still nothing after it was free. Ok there are 2 what look like capacitors. 1 large silver one with lots of wires and 1 smaller black with 2 wires comking to it. Would one or both of these be bad?

[ScottG]

borgy wrote:
So should I try the squirrel cage fan first or fan on top unit first?

Same thing - they're just on opposite ends of the same shaft.

[borgy]

So should I try the squirrel cage fan first or fan on top unit first?

[ScottG]

I should add that it will also do exactly as you describe if the start cap pukes. So if the fan isn't stuck, that would be my next thing to look at.
By the way, you can use the fan to check it but don't use either fan (in or out) to force it. It will break.

[pianotuna]

Hi,

With the power off (unplugged) remove the inside cover of the AC. Put your hand in and give the squirrel cage fans some help turning. It doesn't take long for the fan bearings to be an issue.

[ScottG]

I always have to climb up on the roof every spring and break the fan shaft free. It rusts up just enough that it wont turn. Oddly enough, my last unit worked fine for 13 years of doing this.
So first thing to do is crawl up on the roof, remove the AC cover and see if the fan spins. If not, break it free with some vice-grips and lubricate the bushing as much as you can.
Then it will be fine for another year.