Thanks, Rio Dan ... great information! I've previously replaced capacitors on pump motors and that's not to difficult. Is this capacitor something that I can replace myself? If so, where can it be accessed ... from the top or bottom of the unit? Is the capacitor something that can be purchased online? I assume that it can be tested for a short thru the use of a multimeter ... an ohm range for a good capacitor and it's bad if it tests outside of that range, correct?
Thanks again!
First let me qualify: I'm not a TM owner yet, hence my guest status. And it's been a while since I've had an RV rooftop AC unit open. I work on bigger stuff.
Safety first: Make sure power is disconnected to the AC before removing panels! Capacitors are like batteries and can hold a charge. Always discharge the capacitor by shorting the terminals before touching them. You may even see a small spark when discharging a capacitor. This is normal.
I'm not sure if the capacitor(s) are accessed from the top (removing the exterior cover) or the inside (removing the interior cover plate). It may vary by manufacturer as well. There may be two capacitors, one for the compressor and one for the fan/blower motor. Or there may be one dual capacitor. If so it would have three terminals as opposed to two for individual capacitors. They usually have push-on terminals. When you open the unit find the wiring diagram. It will be helpful in locating and identifying them.
Testing a capacitor with a volt/ohm meter can be tricky. Unless you have a capacitance meter you can't directly measure a capacitor’s value. Unless the capacitor is dead shorted a digital meter is mostly worthless. If you have an analog meter (sweeping needle type) you can see if the capacitor is "good or bad".
Discharge the capacitor by placing something metal across the terminals. Remove the wires and discharge the capacitor again. Set your meter to ohms and place the leads on the terminals. If the needle swings up from infinity and then back down the capacitor is working. It may still be out of range of it's intended value but it's working as a capacitor should. If the needle doesn't move try some different ohm scales on your meter. Be sure to discharge the capacitor between checks. If it still doesn't move it's bad/open. If the needle moves all the way to 0 ohms and stays there it's bad/shorted.
On dual capacitors one of the terminals is common and should be marked with a "C" or Com. When you test this type one meter lead will always be on the common terminal.
If you find a bad capacitor Google the part number printed on it and you should be able to find at least one or two suppliers.
If your capacitors test good you can always take them to a variety of electronic repair places and ask if a technician can measure their values to see if they match the values printed on the cases.
If the capacitors are good and the compressor still won't start check the tightness of all the electrical connections. When the compressor hums and then goes silent it's tripping a thermal switch inside the compressor on the motor windings. It takes a few minutes after the switch trips for the windings to cool down and reset. The more you trip it the longer it takes. So if you energize the compressor and nothing happens the windings are still too warm and the thermal switch hasn't closed yet.
If all is good and the compressor still won't start then the compressor motor has likely suffered some damage. There is one last thing you can try before condemning the unit. HVACR supply houses sell something called a start kit or hard start kit or boost kit that can be added to the unit to help the compressor start. They cost more than capacitors but way less than a new unit. Tell the counter guy what it's going on and if he’s good he can recommend the appropriate size start kit. Install it per included instructions. It's not a repair, it's a patch. But I've used start kits on verified damaged compressors that wouldn't start and several of these compressors are still running many years later.
Hope this helps.
