[Chester Stone]

When I turn on my front air, it operates and cools for awhile, then it quits cooling, but is still blowing air into the coach. Then strange noises are emitting from the A/C bay. Sometime, it blows both breakers for compressors 1 and 2. I looked into the control panel and found nothing burned. However on the control board, it has a label that says 20 amps for both compressor 1 and 2, but the breakers in the back of the coach are only 10 amp. I am scheduled to see Eddie in Texas on May 20, but I will need A/C for the 10 days before. Any help or suggestions would be appreciated.

[Chester Stone]

Checked more closely and found that the front A/C cools when first turned on, but observed that the condenser fan is not running at a high speed. I now suspect it is the fan or as Tom suggested, the starting capacitor may be bad. I will attempt to check them out tomorrow. In the meantime, Tom stated that both he and Russ had four 20 amp breakers for the two A/C units. We have the same units. I would appreciate it if anyone who has these same units would post the size of their breakers. Also, has anyone taken the A/C unit apart to remove the condenser fan? If so, please confirm is the top of the unit has to be removed for access. Looks like a big job.

[folivier]

Just looked and all 4 breakers are 20 amp.

[Richard]

Is the sound you hear a loud buzz? You already said the condenser fan is not turning. Replace the start cap as you already figured out. A quick and dirty way of checking it is to start the fan spinning by hand if you can do that safely with a stick or other help. If you spin it and the fan starts and runs then almost always is the start cap. Before you remove the start cap. Turn off all power to unit and confirm with voltmeter. Then take a screwdriver and short the terminals of the cap. That will save you a nasty shock. Take a picture and draw yourself a wiring diagram. Most ac supply houses will have what you need. There are two ratings on most caps. Try to match both.

[encantotom]

i replaced all 4 starter/run caps when we had the circuit boards out for replacing the relays (thanks to russ)

i think i paid 5-6 bucks apiece for the caps at the local hvac wholeseller.

they were not bad, just preventative since i am sure they were original.

tom

[RussWhite]

Chester,

Nameplate data, documentation, and current measurements all show that the current draw for an A/C compressor is greater than 10 amps. So, 10 amp breakers would not support the load and would just trip. I'm not sure what is going on, but I will wager the breakers are rated above 10 amps. You also said the condenser fan was not running at high speed. Does this imply it is running at low speed and you are not convinced it is switching to high speed on stage two cooling? If that is the case, then the starting capacitors are not an issue, although changing them out for new is both easy and inexpensive. The difference between low and high speed on the fan is mostly easily observed by opening the bay door and running the unit in stage one cooling. Do that by making the thermostat setpoint only 1 degree above actual temperature. Then, move the T/S setpoint several degrees above actual and you have 3 minutes to get in position at the unit to hear the change in fan speed. You should hear the second compressor come on as well. I found the change in fan speed to be smaller than one might imagine. The fan current changed only about one amp as I recall.
You didn't mention it, but do the breakers ever trip? If the breakers don't trip and the fans run at all I would lean toward circuit board relay problems or connector problems. As you gather more information I hope we can be more helpful. Russ

[Chester Stone]

Thanks to all. I will change out the breakers today and do the testing that Russ suggests. Will report back.

[Richard]

So this may or may not be the problem, but this is a common situation so let me explain. If the condensor fan does not come on, the compressor will come on but in short period the pressure will spike on the high side of the compressor and the high pressure limit switch will turn the compressor off. The current is still on to the fan, after a while, one of two things will happen. You will overheat the breaker and it will trip or you will burn up the fan motor.

Before you start replacing breakers, hang the ammeter On the circuit and see what it is drawing at start up.

[Chester Stone]

I replaced the breakers to 20 amp. The back a/c works great. The front a/c compressor, on high fan, runs for a few minutes, then the condenser fan starts up and everything runs for about 20 minutes, then everything shuts down except the fan pushing air to the coach. While running this 20 minutes, the condenser fan seems to put out substantial air, but has a high pitch noise reminding me of a bad bearing. The breaker did not trip. Richard, I will work on it tomorrow and try to pay attention to the amp draw. Russ, I followed your instructions on the rear a/c and it performed as you suggested. I will attempt to do the same tomorrow on the front air.

[RussWhite]

Well Chester that sounds like progress. I think you have picked the low hanging fruit and it may get tougher from here.

It may help to try and take it slowly a system at a time. By that I mean just start trying to figure out what is going on with the stage one components - that's low speed on the evaporator fan, low speed on the condenser fan, and compressor number 1 running. Remember, if you have not changed thermostats, just select AUTO Low Fan and you get only stage 1. It is not easy to get a clamp-on amp meter around the wires going to each of those motors. Do you think you can do that? If so that will help you understand what is really stopping after that 20 minutes. You know the evaporator fan is still running, but it would be difficult to tell when the condenser fan stops if the compressor motor has stopped or not. Probably you could tell by listening outside at the unit, but a meter would be better. As Richard already said, if the condenser fan does stop with the compressor still running this will eventually overload the compressor motor due to high head pressure. I wonder if those motors have any kind of internal thermal overload protection. If they do it is probably self resetting as there is no way to get to a reset button that I know of.
It would be nice if you had a spare control board to swap into the front unit to see what that would do.
The high pitched noise can't be good. I have posted below current readings taken from my units that are operating normally.

Compressor #1 8.7 amps Compressor #2 9.0 amps
Evaporator fan High speed – 3.4 amps Low speed 1.7 amps
Condenser Fan High Speed - 2.8 amps Low speed 1.9 amps

Russ