SCS Basement Air Owners Question

RussWhite · 07-03-2010, 12:30 AM

If one of the compressor in the dual compressor configuration on each SCS basement air was not running, how would you know?

I just stumbled upon the fact that one in each of my units was not working by using a clamp on ampeter on the breakers. Not something most folks would be doing.

Russ

Richard and Rhonda · 07-03-2010, 11:01 AM

Russ,

I don't have the SCS units, but if you do have a problem, they are literally right down the street from me. If I can help in any way let me know.

I don't know how the SCS dual unit is supposed to work. I am curious if the control unit was calling for power on the second compressor. In my pea brain, I am thinking if there is a problem with the compressor, it will either show locked rotor amperager or trip the breaker. Of course the windings in the motor could be shot and it's not making a circuit. I would verify how and when the second compressor is supposed to kick in before I decided I had a problem.

RussWhite · 07-04-2010, 02:47 AM

Thanks! Always nice to know someone involved in the RV game is still in business. I'll tell you what I think is happening, and later follow up with whatever it turns out to be.
The thermostat is a two stage one that has an output for compressor one and a second output for compressor two. When the setpoint and actual temperature diverge too much, the second compressor is requested to run. The second compressor will be prevented from running if low speed for the fan has been selected on the thermostat. Having taken all that into account my second compressor will not run when called upon by the thermostat to run. Using a voltmeter I can see there is no voltage going to the compressor so that is why it could not possibly trip its breaker. I am guessing that the relay that should energize to start compressor number two has burned contacts. It is an inexpensive printed ciruit board part and I have it on order. I'm hoping once it is installed compressor two will at least get voltage and then we'll see if it runs or has some other problem. Stay tuned...

Richard and Rhonda · 07-04-2010, 04:34 PM

A Ha.

Even though I have Dometic basement air, I had exactly the same issue. Contacts in relay mounted on circuit board were toast. I confirmed by apply voltage to relay trigger and ohming out the relay. I got through the weekend by bypassing the relay.

I ordered spares and keep them in the coach along with a soldering iron. You may or may no have removed something from a board before. For those who have not, buy soldering wick at Radio Shack or some other place. Put it between the iron and solder joint. It will suck the solder out of the hole. The part should literally fall off the board if you have done it correctly.

Russ, you might also want to check something while you're in those control boxes. For some reason, the wire splices where 120 was going to the compressors were loose. I had a melt down in one my three boxes. Obviously bad connections at that juncture drop the voltage and up the amperage. I suspected that may have been a contributor to my burned relay. Anyway, check those wire nuts while you're in the box.

express1 · 07-04-2010, 05:17 PM

You guys are way to deep for a holiday weekend!!!
Have a safe 4th!!!!

tuga · 03-24-2011, 12:45 PM

I found a burnt wire on my rear AC (SCS basement unit) circuit board. Can anyone tell me where I could find a new plastic connection (I already have a spare c.b.). Looks like the circuit board is finished. The burnt wire goes to Comp 1 on the c.b.

Also, why would the wire that is connected to the circuit board burn?

What should I check?

Richard and Rhonda · 03-24-2011, 02:23 PM

Tuga,

Can you post a picture?

The burned wire is caused by high current. High current can be caused by loose connections. Check all the wiring connections to AC power in the control box. I have found all of mine loose. It seems to be a common problem with the era in Newells. I had melted wires in two of my three control boxes. In two cases it caused the relay on the circuit board to overheat.

RussWhite · 03-25-2011, 02:07 AM

Tuga,

I would put it a little differently.... The burned connection is most likely caused by normal current, but high resistance. When a connection's resistance increases due to insufficient contact area or contact contaminates, the resistance increases and you are in trouble. Once the connection gets too hot the resistance only increases and this snowballs with the result often a total failure of the connection.
If you can identify the maker of the connector you should be able to purchase from the many online electrical suppliers. I don't have the connector in front of me at this time, but another options may be to just purchase new pins/sockets and replace them in the plastic unless the plastic itself has been damaged. I was able to improve the connectors by resoldering the portion that attached to the circuit board. You always have the option of purchasing a better quality connector with pigtails on both halves and solder one set to the board and splice the other set to the existing wires and then just plug and unplug near the board rather than at the board. Without seeing the damaged board I can't be sure, but it would have to be very severe damage that would keep the board from being repaired. Even when a "land" is burned open one can solder a wire in its place and return the board's functionality. Good luck and if you get stuck let me know, and when I get a chance, I will pull mine apart and see if I can suggest a supplier for the connector. Russ