BAC Forum
General Boards => Technical Support => Topic started by: Dick Simonis on September 13, 2014, 11:49:11 PM
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Now that I'm moving closer to picking up the 2002 Marquis my mind is already looking at upgrades. At the top of my list are the thermostats.
The basement air and furnace has an SCS thermostat for controlling the fan speed and AC unit. While it has a set point display it does not have room temp readout which is annoying. Right beside the thermostat is a switch for AC high and low which I'm told controls how many compressors (1 or 1) are to be used.
I know I can substitute a heat pump thermostat to control the temp and fan speed (I did that on mt current PT) but would it be possible/practical to also control the compressors....say when the fan kicks to high speed it also turn on the 2nd compressor. Conversely as the temp nears set point the fan slows down the the second compressor stops.
Has anyone else upgraded thermostats??
Thanks
Dick
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Dick,
There are very few thermostats that are compatible with the SCS A/C unit. The thermostat not only controls when the second compressor is engaged, but it also controls the condenser and evaporator fan speeds. The second compressor only runs when the thermostat senses the primary compressor can not handle the load. If the interior temperature rises more than about two degrees above the set temperature the thermostat engages the second compressor and activates high fan speed if the thermostat is set to high fan. The fans only go to high speed when the second compressor is activated, regardless of thermostat settings. So in other words, leave the thermostat alone.
Gerald
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Well shucks, it looked like a good idea on the surface. Thanks for clearing this up Gerald and I will take you advice but still miss the ambient temp readout on the display.
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I have an indoor/outdoor thermometer placed where I can see it while driving and while watching the living room TV. The outside temperature sender is hidden inside the automatic Girard awning out of the sun and weather. Also, the Aladdin has a basement/outside thermometer on one of its screens. I have been thinking about putting another indoor/outdoor thermometer in the bedroom.
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Dick,
There were two different thermostats that Beaver used with the SCS units. The one that I have in my coach has the ambient temperature on the thermostat, but only when the thermostat is set to heat or cool.
Gerald
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Thanks guys I will look at it in more detail when I get back to bend this week. Honestly, this whole basement air thing has me a bit nervous but with good reports from other users I'm feeling a bit better.
Of course, the AC unit is not working and will be pulled for repair/replacement as part of the PDI so perhaps I'll get an opportunity to speak with the chap BCS uses for his purpose. I will speak with them about the thermostat options as well.
I do like the idea of the weather station and I never though about putting the temp sensor in the awning housing. Any more info on where that went would be appreciated. Speaking of weather stations, my Sliverleaf on this coach has the weather channel but the new one does not...I'm going to miss it so an aftermarket sounds rather attractive. Thanks for the suggestion Dave.
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Like David, I have an "atomic" clock with an in/out temp and humidity monitor (LaCrosse I think). I've had Oregon Scientific brand in the house, but recently they've gone to a screen product line-wide that is too dark for us to make out the digits on, so I won't buy their stuff anymore.
To get the outside remote sensor to a neutral position where direct sun or rain would affect it or its readings, I fastened it, via velcro I think, to the top of a frame brace alongside the genset. It's easy to get at for battery changes, is reading mostly shaded ambient air, and is protected from most harm. I don't really have the base unit where it's visible while driving because I use the Aladdin for that, but while camped it is handy to have on the buffet or a wall. The only minus is you obviously can't rely on the outside reading while the generator is in use and warmed up, but for us that is pretty infrequent anyway.
Joel
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I have an indoor/outdoor temperature fastened to the side of the bay that comes out with the slide. Its not a good place, because in direct sunlight (which seems to always be on that side in most campgrounds, the metal surface heats up and shows the ambient temperature as over 100 degrees.
I don't want to put it inside the generator housing either. Any good suggestions?
Stan
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As I indicated above my outdoor sending unit is inside the cover of the automatic Girard awning. Specifically, it is velcro-ed inside the trailing end of the cover that travels in and out with the awning when extended. While that is a good place because it's out of direct sun and weather, it is also adversely affected by the sun when it shines directly on the outside of the awning cover.
I was thinking perhaps placing the sending unit in an unheated basement storage compartment. I have two, both sides behind the AquaHot on the curbside and behind the propane access on the street side. Because those storage compartments are usually closed I would guess the temperature inside the compartment might be slow to change with the outside temperature though. But the sender in a compartment is out of direct sun and weather there.
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That's why I put mine on the front cap support frame alongside the genset. It isn't in an enclosed bay, but rather in a place where ambient air from outside can get to it being it is all open underneath. Yet it is not near an outside surface where its sensor gets compromised by the effect of sun, direct wind, or rain. The idea is to read as close as possible the actual, relatively uncompromised ambient air temperature. The only time that isn't the case here is if the genset is used, although some minor effect from wind, pavement reflected heat, and wet weather may be there when on the road. But as mentioned previously, I don't rely on the device while driving anyway.
I think we're getting off course from Dick's original post.
Joel
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For those that might be interested, I spoke with the tech that is repairing the basement air (control board relay) and asked about replacement thermostats. He has successfully used a Honeywell pro 5000 two stage unit that apparently works very well. Later today when he is here to install the board and test the AC, we will discuss this more. I just might have him do that before we leave.
I'll keep you posted.
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Dick,
Did you have the thermostat replaced? If so, does it work well?
We had a weird AC problem today and it seemed to be caused by the T'stat, although I don't quite understand how. We're in a park on 30A service. This afternoon the breaker on the power post tripped. I reset it and it blew again as soon as the AC (basement air) kicked on. I turned the AC off at the T'stat and at the breaker panel, reset the power post CB and checked the ac readings on the CMP. Saw 115V on both circuits and AC 1 drawing 16 amps & AC 2 at 12 amps. I fired up the generator to see what kind of draw I'd get with 50A available and saw no difference in the readings. Went to T'stat and worked selector switch up and down a number of times and the CMP readings became normal; AC voltage & current on Circuit 1 and nothing on AC 2. Killed geni and went back on shore power and all is normal with working AC. Not clear to me how T'stat causes this but?? Will replace T'stat when we get home. Anyone know what direct replacement is, if not the Honywell 5000 Dick referred to?
Thx, Steve
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Steve,
There are some delay cycles built into the control systems to protect compressors. They usually occur after the compressor shuts down and will prevent it from coming back on again for a few minutes. In your case you lost power and then could not shut the compressor down immediately. Due to the loss of power you may have been in one of the delay cycles even though the compressor was running when you restored power and the thermostat could not force the shut down. You may want to see if all is working and repeatable with normal power for awhile before replacing anything....you had a strange power event and the control systems may not be designed to handle it.
Later Ed
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Steve,
I have not done the thermostat replacement yet but it's on my list. I'm still pondering just how to incorporate all the functions but may either dig into it more during our 2 month stay in OR or wait until I get home and get some help from Fred.
As to your problem, I'm almost betting you have a weak 50 A breaker on the pedestal. The time delays Ed mentioned don't seem to be an absolute and, on mine, the delays only occur when initial starting the AC unit. If the cool switch was "off" than it delays when starting. After that both fans and compressors may start simultaneously. In that case, the surge current may be more than the breaker can handle.
Just a guess of course but if this is the first time it's happened on this pedestal than I might not get too concerned.
Keep us posted and good luck.
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Problem occurred again today. Found that neither AC breaker in the AC panel had any effect on current readings, but water heater breaker dropped AC 2 current to 0. Then I remembered reading someplace that the # 2 compressor would turn on if set temp was 2 degrees below ambient. This was the case in our situation. Reset power post, turned off water heater, and started AC with set temp 1 degree below ambient. It has continued to run. Reached set point and I reduced set point another degree. Still running.
Can't believe that there isn't a relay to keep compressor 2 off when on 30 amps. Also don't understand why water heater breaker apparently supplies AC to air cons and air con breakers have no effect. Wiring diagram sure would be nice.
DW not happy.............. :(
Steve
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Steve, I currently struggling with the 30A thing. I found that you can not turn one breaker off...it appears each breaker provides some necessary power and the high/low switch doesn't do anything that I can figure out. Right now I'm running the system with the switch set on low and being careful not to let the temp get above 2 degrees from set point. I also keep the fridge on gas and the aqua hot on diesel only.
I have found the Marquis to be a real AC power hog.
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Dick,
Good to know someone else is "sharing the pain". I'm going to dig into this when I get home and try to find out why comp #2 gets any AC when on 30 amps. Doesn't seem to make sense to me.
Thx, Steve
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Steve,
You have that ability with your thermostat. Just set the cooling fan selector on low speed using either auto or on position. On low fan speed the unit will only run one compressor. You can also just go to the breaker box in the rear closet and turn off the breaker for the secondary compressor since the fan motors run off of the same breaker as the primary compressor.
Gerald
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Gerald,
Thanks!
Steve
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Dick - Our Marquis is "a real power hog" too, as you put it. Many times the generator auto start will activate before we can get set-up when boondocking.... and this is immediately after a couple hour drive, so all the batteries are charged up when we park. The six-pack of golf cart batteries supply a lot of power, but it seems not enough to run the coach for very long... maybe 45 minutes.
We don't know where all the power is going. Over the last couple years we have adjusted to it by unplugging the insta-hot and tried to keep other plug-ins at a minimum... like the computers and phone chargers.
What we have finally done to adapt is to defeat the problem as cheaply and effectively as we can. We purchased a 3,000 watt, 75' remote start, 4.6 gallon fuel tank capacity generator which is kept in the back of the toad. The Marquis's power cord reaches the generator easily with the toad hooked up in tow. We can park, hook up and start the remote generator, extract the slides, level the coach, etc. and leave the generator running. Obviously, when we boondock we park such that the running generator sitting on the tailgate of the Avalanche will not bother other campers. This generator soon settles down to generate only 20% of its capacity - enough to have power for two TVs and the fridge on 110v. The 4.6 gallon gasoline tank will run for 20 hours or more if I leave it on. It's cheaper than paying to stay in a $30 per night RV park. The downside is every couple days we need to fill our gas cans.