SCS Basement Air problem and solution

[David and Teresa]

I have just had my basement SCS air fixed and the solution may be important to someone.

The dual compressor unit was giving us trouble recently, not blowing as cold as the single front unit and the fan wouldn't turn off. I called my house ac service company and persuaded them to service my coach. The tech traced the problem back to a faulty thermostat. I told him I would order one and call him back for the install.

Victory Climate (who has the remaining SCS inventory) sold the final 3 thermostats to Newell last year. I called Newell and the thermostats they have don't match my coach. I was told a Newell owner was able to make them work with a lot of effort but Newell didn't know how they did it. Newell knew of no other solution or replacement thermostat. Being 12 volts instead of the common 24 volts for home units seems to be the problem.

I then called PGS Controls (the thermostat manufacturer for SCS). They didn't have any units but the engineer looked at the original specs for the thermostat and suggested that a battery supplied house thermostat should work.

I called my home ac service company, told them, and their engineering department said it would work.

So, we purchased a Honeywell FocusPRO TH5000, a battery operated, 2 stage thermostat (uses 2 AA batteries).

We installed it and it works perfectly with one change. The old system had a 2 stage fan and this fix can only have 1 stage fan, which, because we're in Florida, we chose high.

Also, before my tech came for the final time, I made access to the basement ac on both sides by cutting out large access holes (covered by new aluminum panels with 4 screws). When he checked out the compressors, one had a burnt wire.

So problem solved, ac as cold as I've ever had, and way cheaper than a coach service center.

David

[tuga]

David,

I had an AC tech changing my circuit board on my SCS front unit, he told me that if I ever had trouble with the thermostat to just replace it with one from Camping World. He said that Coleman makes a 12 volt thermostat, but any brand would work as long as it is 12v.

Glad you found something that works. I am going to keep the model number you posted in my files, just in case the Coleman 12v thermostat doesn't work.

You never know.

Good Post, thanks.

[RussWhite]

"We installed it and it works perfectly with one change. The old system had a 2 stage fan and this fix can only have 1 stage fan, which, because we're in Florida, we chose high."

I think you probably lost a little more than just the low speed of the evaporator fan. The controls were designed to limit the compressors to only stage 1 when the fan speed switch was in the low position. This is explained in the manuals for the air conditioner and can be handy if one is trying to manage power consumption.

I did purchase a spare thermostate from Newell that was advertised as a replacement for the originals in my coach, but actually lacked the low speed fan option just as your replacement does. At least it works on 12vdc. I have tested it and know how to connect it should the need arise in the future.


"Also, before my tech came for the final time, I made access to the basement ac on both sides by cutting out large access holes (covered by new aluminum panels with 4 screws). When he checked out the compressors, one had a burnt wire."

This is interesting. So you found a way to access the compressors without removing the air handler, is that right? If so, I sure would be interested in your posting a picture of where you cut the access panel.

Thanks, Russ '99 #530

[David and Teresa]

Here's a photo of the Driver's side access. I'll post a photo of the other side when I finish.

[Lewis and Clark]

Hey guys,
I have a 1996 Newell #410 with the same basement AC set up. Everything was running fine until the other day. When the second compressor kicks in on the 2 stage unit, the condenser fan does not shift to high, it stops completely. I opened the unit up and took out the circuit board but did not find anything unusual, i.e. burnt connectors, etc. Do you think the problem is with the thermostat or the circuit board? Can someone explain exactly how the thermostat works? Any input is appreciated.

Thanks,
Nando Garbarino
Ft Myers, Florida

[Neweller]

Nando,

A thermostat's basic function is to regulate the operation of heating and equipment in your home. You set the thermostat to the desired temperature and the thermostat turns the equipment on and off to maintain that temperature. A thermostat is essentially an automatic switch. The thermostat senses the temperature and turns the air conditioner or heater on and off as required to maintain the desired temperature.


There are two basic types of thermostats: electromechanical and electronic. They both do the same thing but they do it in different ways. Additionally, of the two basic types, there are several varieties from which to choose.


An electromechanical thermostat typically uses a bi-metal coil or strip which moves as it expands and contracts with temperature changes. Mounted on the bi-metal strip is a glass vial partially filled with mercury. As the vial is tilted on the back on the bi-metal strip, the mercury flows to the end of the vial where two electrical contacts are exposed. When the mercury envelopes those electrical contacts, a low voltage circuit is made, thanks to the fact that mercury is conductive. This works just like a light switch and makes a circuit to turn on the heater or A/C.


An electronic thermostat operates in much the same way as an electromechanical model except that instead of the moving bi-metal strip and mercury switch, it uses a sensor to detect temperature levels. When the temperature differs from the preselected temperature the thermostat electronically makes the circuit to the heater or A/C.


Also, here is a link to an online circuit board repair center. As I understand it, you just send in your circuit board and they will test and repair it, and then send it back to you. They have a pretty good turn around time.

http://www.acsindustrial.com/printed-circuit-board-repair.php

Let us know if any of this helps.

[RussWhite]

Nando,

I am an electrical engineer and have repaired my circuit boards and understand the system fairly well. With the information you have given in your original post I am fairly certain the problem is not with the thermostat. That leaves the board and its components and the motor itself. My experience has been the circuit board is not well designed and is boarder line for switching the current loads that it is required to control. I have replaced the switching relays and repaired circuit traces that were burned with additional wires and solder. It is easy with my background, but not so easy to detail in a post. I was able to find the relays that were used on the board on the internet and obtain them at a very reasonable price. My A/C manual included a schematic and wiring diagram for the circuit boards and well as an english language description of the proper sequence of operations. Should you desire to attempt to troubleshoot the board and repair on your own I would be glad to try and assist. Good luck. Just remember if you can use a voltmeter you would be able to determine if the board is bad, or the motor has the high speed winding burned open. Russ

[Lewis and Clark]

Thank you all for your responses. Today I determined that the winding on the motor are working. I connected 110V directly to the condenser plug and achieved both low and high speeds. I guess I am at the point of removing the board and sending for repair to the site that Ken suggested.
With your knowledge of this board, is it possible to jump or connect directly the high speed fan?

Thanks,
Nando

[RussWhite]

Nando,

Congrats on learning the fan motor is okay - I suspected it would be. You are probably looking for a way to stay cool while the board is out for repairs and I think that will be difficult. If you just wanted to leave the board installed you might be able to solder a jumper across the high speed condensor fan realy contacts, but the problem could still be somewhere else like at the connection between the board and the condensor fan connector. It would be a major expense, but you could purchase a board from Newell and install it and then have your board repaired. Then you would have a spare or at a later date I suspect you could sell the board for what you have to invest now as the boards become harder to find. I would not want to be without my A/C right now for sure! Russ

[Lewis and Clark]

Checked with Newell already and they have no more boards. Their solution was for me to install roof mounted units.
Therefore, the only solution is to repair the one I have and keep looking for another board to have repaired and keep as a spare.

[Lewis and Clark]

FYI... ACS does not repair circuit boards for AC units. I have contacted U.S. Electronics Repair in Baltimore MD and will keep you posted on the out come.

Nando

[RussWhite]

Nando,

If you can't find anyone, I will do the repair for you.

Russ

[Lewis and Clark]

Thanks Russ, hopefully I will not have to bother you. I will post the results when I hear back from Baltimore. I sent the board today overnight should hear results on Wednesday.

Thanks again for you offer,

Nando

[Lewis and Clark]

Received the board back Friday, installed and still no high cond. Fan. Sending board back to US Electronic for another look. Keep you posted.

Nando

[RussWhite]

Nando,

That was disappointing I am sure. My setup uses two identical basement systems as it is easy to swap parts when one needs to prove a point. If you could swap circuit boards and the fan then ran on high everyone would know the board was the problem.
Did you send a schematic with the board to the repair folks? If you need one, let me know and I will email in pdf format to you.
Good Luck, Russ

[Lewis and Clark]

Hello Russ,

Yes I sent a copy of the schematic with the board, I spoke with the owner of US Electronics Friday and he himself will check the board Tuesday. He is sure it is in the board seeing that the 2nd compressor comes on and the only malfunction is the condensor fan stopping. Hopefully he is correct and can repair. I will keep you posted.

Thanks,
Nando

[tuga]

Nando,

That was disappointing I am sure. My setup uses two identical basement systems as it is easy to swap parts when one needs to prove a point. If you could swap circuit boards and the fan then ran on high everyone would know the board was the problem.
Did you send a schematic with the board to the repair folks? If you need one, let me know and I will email in pdf format to you.
Good Luck, Russ

Russ,

I would like a pdf copy of the schematic for the AC.

tugagaidry@bellsouth.net

[Lewis and Clark]

Hello Russ, I got the board back again. I installed it and everything is running as should.
The only issue I have is when the single unit and double unit is running for an extended period of time (2 to 3 hours) the breaker at the pole trips and is every hot. I switched poles but the same outcome. When the single unit and the low side of the double unit are running it will not trip the breaker.
The temp. is 96F outside and I am in the direct sun with no shade if that has anything to do with it.
The double unit it pulling 28 - 30 amps. and the single is pulling 16 - 17 amps.
Any thoughts?

Regards,
Nando

[RussWhite]

Nando,

Well the second time was the charm and I am glad they got your board fixed.

I need you to answer a few questions before I can give any thoughts.

I understand the outside temperature and your lack of shade - makes sense that this would require most is not all of your coach's cooling ability.

Do you have two SCS basement units, each with two compressors? That is my setup. If so, these are two stage units with identical compressors and two speed fans. When second stage cooling is called for - and that happens anytime there is more than a two degree difference between actual and setpoint temperatures, both compressors run and both fans run on high speed. This assumes you have the thermostat set for fan high.

Now the fans draw about 2 to 3 amps on low and 4-5 on high. Each compressors draws around 11 - 12 amps. So one unit running on high is in the neighborhood of 27 amps or so.

With that I need to know what kind of service you have at your power pedestal. If it is just a single phase 30 amp service you are obviously in big trouble and the breaker tripping is just what it is designed to do. But, if you have two phase 50 amp service we need to dig a little deeper as that should support two units on high assuming you do not have any other big loads at the same time. My coach is interlocked such that I cannot run my airs with the AquaHot on electric as this with other loads could trip even a fifty amp service.

Get back to me with a little more detail and we will go from there. Russ

[tuga]

Nando,

I might add to Russ' post. Check your inverter charging setting. There are 3 levels of charging your house batteries using a Link 2000 remote display (usually it is located above the microwave or across the hall from the microwave). 30, 20, & 5 amps.

The first choice is to charge at 30 amps, this is where most systems are set. If yours is set at 30 amps, try turning it off completely and see if you trip the 50 amp breaker outside. I'll bet you the ACs will run all day without tripping. If your ACs are using 27 amps on each leg that only leaves you 23 amps per leg. You can now see where having the battery charger in the inverter set at 30 amps is tripping your breaker.

During the summer months, I keep my inverter/charger set at a 5 amp rate of charge. That enables me to run both ACs on high without tripping the outside breaker. You can change the setting using your Link 2000 very easily. If I remember correctly, you press and hold the setup button until the display starts to flash, then you quickly release the button. The current setting will display (let's say it is 30 amps); press the button and toggle thru from 30 to 20 to 5 and then let the system automatically go back to the regular display. Your charger is now set to charge at 5 amps instead of 30 amps.

Verify my instructions above with your owner's manual - all set ups are different.

Keep in mind that your stove, washer/dryer, refrigerator, TVs, etc. all draw amperage. You only have 100 amps total to use 50 on each leg; actually, it is more like 80 amps total 40 on each leg. Watch your amp meters on the panel above the driver's seat. When you are approaching 40 amps on each leg it is time to turn something off.

[RussWhite]

Tuga,

You proabaly are clear on how your charger functions, but I'd like to clarify a few suggestion you made. The power supplied to a bank of batteries to charge them is measured in amp-hours. The process of charging is necessary to replace amp-hours used from the batteries when not connected to an AC source, either the pedestal or your generator. The only other need is the very small amount to replace internal loses within the batteries and maintain the float voltage. The paramaters you are suggesting to change determine the MAXIMUM current that will be delivered to charge the batteries. This means that if you have been dry camping and your batteries are in need of charging the time it will take will be very long due to a very low charging rate. Conversely if you have not been dry camping and your batteries are charged ( like almost everyone plugged in ) they will not be using any signifcant current regardless of the MAXMUM setting on the inverter. Once the charger reaches third stage ( float ) a bulk charge that could be affected by the settihg of the maxium charge amps paramater will not be initiated except by a power interruption. This all assumes a healthy battery bank. A bank with bad cells might not reach full charge normally and could just waste charing current as it is turned into heat in the bad battery bank. Whith my battereis full charged ( as they are almost all the time ) changing the maximum charing amps paramater makes no difference what so ever on my power consumed. Russ

[RussWhite]

Nando,

Watch your amp meters on the panel above the driver's seat. When you are approaching 40 amps on each leg it is time to turn something off.

I was disappointed with my coach #530 when I did not have meters to observe amps used in each leg of the power system. Mine was dumbed down to just idiot lights that are on when power is on. I still remember the fist Newell I ever saw year and years ago and how impreseed I was with all the meters in the electrical controls panel. I wonder if the meters have come back in later coaches. I chose to install a power management system to provide some protection and that included a remote display panel that shows amps, volts, and frequency for shore power. The idiot lights have black tape over them:D

[rheavn]

Russ,
"No two Newells are the same". What you have in your coach was decided on by the original owner and not Newell unless yours was one of the few show coaches. Ours were built at the same time & mine has the amp and voltage meters for each leg and the idiot lights. If you got the original build sheet with your coach it is very informative in seeing the many choices & decisions they had to make. These things are so custom that the chance of two owners making exactly the same choices is probably in the one in a million range. One thing about buying used is you don't get EVERYTHING you want--there are things in mine I would have ordered differently.

[Lewis and Clark]

Hello Russ,

My coach has 1 single unit (for the front) and a double unit (for the center and back).
Each leg of the pole is 120 -125 volts and 50 amps.
I have the gages above the driver’s seat that I can monitor the incoming volts and amps usage.
With the single and double unit running, line #1 reads 28-30 amps used and line #2 reads between 16-18 amps used. Voltage on both lines reads 120-125. I understand the comments regarding the inverters and since I am able to monitor the incoming and usage, it is not a problem. Also, I never have a problem while on gen.

Thanks again for you help,
Nando

PS. just today I added another battle to the list when I noticed the steering gearbox leaking. Have gotten so far as to determine that it is a TRW TSA 85 now I have to crawl and wedge myself up there to see the last 3 remaining numbers to identify the correct part. At least I am not getting bored, always something :)

[tuga]

Nando,

Just a friendly reminder, whenever you crawl under your coach be sure to block the chassis up with wooden blocks or steel jack stands (20 ton) or use a 20 Ton bottle jack to jack up the frame. If an air bag blows or an air line burst you could be killed instantly.

I knew a fellow who lost his life like that.

Please take the proper precautions to protect yourself. If you are unsure of where to place the blocks call Newell and they will tell you.

[Lewis and Clark]

Tuga Thanks for the heads up.

Nando

[RussWhite]

The only issue I have is when the single unit and double unit is running for an extended period of time (2 to 3 hours) the breaker at the pole trips and is every hot. I switched poles but the same outcome. When the single unit and the low side of the double unit are running it will not trip the breaker.
The temp. is 96F outside and I am in the direct sun with no shade if that has anything to do with it.
The double unit it pulling 28 - 30 amps. and the single is pulling 16 - 17 amps.
Any thoughts?

Regards,
Nando


Then later you say "I have the gages above the driver’s seat that I can monitor the incoming volts and amps usage.
With the single and double unit running, line #1 reads 28-30 amps used and line #2 reads between 16-18 amps used. Voltage on both lines reads 120-125."

This is very puzzling and I am not sure what is going on. A good 50 amp breaker should carry continously most of its rating. Even at a very low 80% that is 40 amps all day long. So why does your breaker trip if you are actually below that amount. If I actually had the same situation as you are describing and I was sure of my current load I would opt to have a new double pole breaker installed. Most campground managers are willing to do this if you are in good standing. I did once have a problem and requested the change and got a less than enthusiastic response that he did not think it could be the breaker. After changing everything was back to normal and I even got an apology. Yes, I read where you tried another pedestal, but it is not for sure that breaker was in good repair either.

Tuga beat me to the advice for supporting the coach. It's a risk not worth taking.
Keep us posted.

Russ

[Lewis and Clark]

Russ, thanks for the response. I agree with your suggestion of changing the breakers. I just wanted to eliminate any unknown to me potential issues.

[encantotom]

circuit breakers can get weak....or break and cause arcing to happen inside which could trip when under heavy load.

where it is most common is if they are

1. used as a switch....they are not designed for that. in a pedestal at an rv park they are turned on and off constantly.

2. overheated by drawing right at capacity. our big rigs can push these things to the max. i bet your coach inside has a 60 or 70 amp breaker and the pedestal has a 50 amp.

as we all know, our house breakers tend to last forever, but generally they are not used as switches and are never under near to capacity loads.

my two cents worth and i am sticking to it.

btw, i recently replaced my swimming pool 220v breakers that had gone bad.

tom

[Richard and Rhonda]

You might want to check both the connection at the pole and the innards of your 50 amp plug I had the same thing happen only to discover I had corrosion within the plug and although the coach was pulling less than 50, the added resistance at the plug was driving the breaker at the pole into overload.

[Lewis and Clark]

Richard, Thanks for the suggestion.

Nando

[JohnC]

Once again, Thanks Russ. Checked with Newell already and they have no more boards. Their solution was for me to install roof mounted units.
Therefore, the only solution is to repair the one I have and keep looking for another board to have repaired and keep as a spare.

As of 11/15/2011 Newell has a limited supply of rebuilt boards for sale. The single control units are $159 plus a $100 core deposit, while the dual compressor control units sell for $189 plus a $100 core deposit. We are temporaily asking you to limit your orders with no core, to one board, so that toghether we can help those whose systems are inoperative. If you have any spare boards needing rebuilt, please contact Creslie or John to make arrangements.

The rebuilt boards come with a limited one year vendor warranty, and have been modified to better handle current flow.

We hope to have 'new' boards available soon, and will keep you posted.

JohnC

[folivier]

John, are yall rebuilding the boards for the old Dometic basement units?
I have 3 old boards that I recently replaced and have no use for them.

[Richard and Rhonda]

Forest,

If Newell, doesn't want them, I would like to have them.