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Author Topic: What is the BTU rating of the A/C coil on MC7?  (Read 2415 times)
oldmansax
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« on: April 25, 2007, 05:10:32 PM »

Does anyone know what the BTU rating is for the front (drivers) A/C coil in a MC7? I know I can measure & rate it but I am hoping someone already knows the answer so I can remain comfortable in my laziness.  Grin

I am thinking about adding a condensing unit for the front to be used when driving into the sun. Coach air was removed when I bought the bus & the two roof tops don't do the job when facing the sun.

Just an idea. I am open to suggestions.
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'82 BlueBird WanderLodge PT40 being rebuilt
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mikelutestanski
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« Reply #1 on: April 25, 2007, 05:37:54 PM »

Hello:  I have tried and the answer is lost in the grey mists of antiquity. I tried carrier transicold and the archives are lost. THe best answer I received was from Lamarr Welch of Welch industries Stockbridge Ga   . He has done this before. You will need to change the expansion valve head assembly. Lamarr can help you with that. 
      You can get from about  9000 btu up to approx 15000 btu.  Thats the best that I could find .
         I have a dash air system in progress but I am using two evaparators . #1 is the original dash unit. #2 is a 17,800 btu unit from red dot which will be mounted in a kitchen cabinet. The condensor is a red dot unit mounted on the roof which is rated at 38800 btu.   I am using a sanden compressor mounted on top of the miter box .   Mr Welch said that this system should net me about 30000 btu in the coach.        Since it is a split system he could not be definite about how each unit would perform . The system is in progress so I do not have any results yet.    If you choose to rate the 7 dash  transicold evaporator I would be pleased to know your results.
    I to have faced the sun when heading through Louisiana and Texas and two roof units does not do the job...  My generator did not like the heat either.     Good luck with your system     mike     
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Mike Lutestanski   Dunnellon Florida
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« Reply #2 on: April 26, 2007, 12:19:12 AM »

I have a 10kw gen powering 3-13,500btu roof tops.  Two are sufficient to 100 degrees.  I have the front one mounted just behind the drivers compartment so I can aim the air right at me.  The biggest improvement for comfort in the drivers seat was a dash mounted 12v fan aimed right at me.  Very satisfied with the comfort of the roof tops.  Didn't put in engine driven A/C because I didn't want to run nearly 40ft of freon lines.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
oldmansax
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« Reply #3 on: April 26, 2007, 04:47:31 AM »

I am not planning on engine driven compressor either. I was thinking about a 110V condensing unit for the front A/C mounted in the spare tire bay. I have a 6.5KW gen so it will not support 3 A/Cs. I could run the 2 fronts while driving & front & rear while stopped. I could do the same, I guess, with roof mounts, but the front one would have to be mounted which means dealing with the three structural supports that are in the ceiling, cutting the hole, etc. I know I could offset the hole but I don't like how that looks. I am just explorering other options. If the original convertor had insulated better, I may not have had this problem. I had thought about a fan but thought a dash mounted one would just pick up the warm air. I may try that first. I would have to have two, one for the co-pilot.

I have a question about the three A/Cs you have. How do you have them wired? There are 2 hot legs from the generator. Do you have two A/Cs only on one leg, & one A/C and all other loads (invertor, charger) on other leg or some other arrangement?
« Last Edit: April 26, 2007, 04:51:21 AM by oldmansax » Logged

'82 BlueBird WanderLodge PT40 being rebuilt
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JackConrad
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« Reply #4 on: April 26, 2007, 05:00:56 AM »

We have basement AC with the closest discharge vent about 2-3' behind the drivers seat in the ceiling. We have a 12 fan installed above the windshield on each side blowing on driver and co-pilot. They pick up the cool air coming out of the AC vent and put it on us. Has worked good so far. Another thought I had, which we have not done, is to install a window AC in the former spare tire compartment and duct the cold air through the defroster vents putting a curtain of cold air between us and the windshield.  Jack
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« Reply #5 on: April 26, 2007, 06:15:15 AM »

Jack,

That is a neat idea. I had not thought of a window A/C in the tire bay. I may look into that.

That is what so nice about this board. Lots of good ideas!
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Delaware

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« Reply #6 on: April 26, 2007, 08:39:04 AM »

Using a window A/C is a cheap way to go.  I just saw a 5000btu (I know a bit small) for $60.00 new at Costco.  They had a 12,000btu for I think about $150.  If you do the window A/C in the bay, just make sure you separate the air intake and exhaust for the condenser well enough to keep from the hot air recirculating back into the unit.

My gen and bus is wired straight 120v.  I didn't want the hassle of constantly thinking about-am I balancing the load right?  The only disadvantage is that I can only use one leg of the 50amp plug.  So I only have 6000 watts of power from the 50amp plug.  But-for me that's enough to run the two A/C's (can run the 2 A/C's on 30amp if the fans are on low) and have power left over.  Have never blown a 50 amp plug breaker. 
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #7 on: April 26, 2007, 11:38:12 AM »

Tom,

There's no reason you can't have the generator wired for 120 and use 220 shore power.  It's all in how you wire up the transfer.

Len
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« Reply #8 on: April 26, 2007, 03:00:32 PM »

There's no reason you can't have the generator wired for 120 and use 220 shore power.  It's all in how you wire up the transfer.

     That is how our bus is wired. The transfer switch is a 50 amp switch (2 hot legs). On the Shore Line connections: red on 1 hot and black on the other. On the Generator connections: black on 1 hot and a jumper to the other hot connection. The Load Center connection: red on 1 hot and black on the other. These 2 wires connect to the hot legs in the load center.
     I was told by a PowerTech service tech that unless you need 240 from your generator it is better to wire it 120 only. Our 10 KW will produce 10 KW on 120 only. If it is wired for 120/240 it will produce 5 KW per leg. They recommend keeping the load balanced to withn 20% if wired 120/240. On our PowerTech generator, the voltage regulator monitors 120 volt. If the generator is wired 120/240, the voltage regulator is monitoring 1 leg and will respond to the the load on that leg only. If the load is unbalanced and the voltage regulator is monitoring the heavily loaded leg, it will ask for an increase, causing a high voltage on the other leg. If the regulator is monitoring the lightly loaded leg, there not be an increase to compensate the the load on the heavily loaded leg. (this applies to our model of PowerTech Generator, your generator may operate differently)  Jack
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oldmansax
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« Reply #9 on: April 26, 2007, 04:34:42 PM »

I need to check how my gen set in wired. I know I have one neutral and two 110V legs, however, it is not 220V between the two legs. It is an Onan Marquis 6.5 gas and I have the book I just have not looked it up. Right now I have the 50 amp shore power wired as normal with each 110V leg going to one side of the 220V panel. As the gen has two 110V legs I just wired one to each side of the 220V panel as well. I am leaving out all the transfer switch wiring for the purposes of this discussion. I don't need 220V for anything. I will look at "da book" & see what my options are.
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DrivingMissLazy
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« Reply #10 on: April 26, 2007, 06:51:50 PM »

The Onan is a different breed than the Power Tech or Wrico. It is not a 120/240 volt winding. At least the one that I have installed as an emergency back up is not, and it is the same model of yours. There are two windings but they can not be connected in series or parallel like the more standard generators can.
Richard

I need to check how my gen set in wired. I know I have one neutral and two 110V legs, however, it is not 220V between the two legs. It is an Onan Marquis 6.5 gas and I have the book I just have not looked it up. Right now I have the 50 amp shore power wired as normal with each 110V leg going to one side of the 220V panel. As the gen has two 110V legs I just wired one to each side of the 220V panel as well. I am leaving out all the transfer switch wiring for the purposes of this discussion. I don't need 220V for anything. I will look at "da book" & see what my options are.
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« Reply #11 on: April 26, 2007, 09:19:04 PM »

I had every intention that as soon as I get that far to use the old 24 volt  2-hp blower motor with a belt to run a smaller sanden
a/c compressor and spin a small fan all in a box that would sit in the spare tire compartment.

I figured the OEM a/c blower power lines would be enough to handle the motor and spin the sanden fast enough to get about 6 to 10k /btu air in the factory drivers air coils. I checked the ratings and the smaller compressor appears to be capable at a 2-hp input, Just haven't got it all built yet. Have the parts, hoses, compressor, pulleys and motor, Just no time to dive into another project yet. Hey it may not work but worth a try just for fun. I figured a condensor off a toyota or something would work also.

Sorry, Just rambling...

Some of the Onan 6.5's were not wired for 220 and only 120 with 2-breakers on the same leg. Something cheap about that deal.
I think that was prior to the new wave of true 50 amp ~ 120/240 coaches. ie; Some MH uses had 2- Roof airs but only a 30 amp cord and panel. There were switches inside that worked only when you had the generator running that allowed both roof airs to function. If you had shore power you could only switch on one air at a time , either front or rear.
I saw this in a 1986 Pace American motorhome and again in a 1988 model. A guy rewired his rig for 120/240 50 amp and proceeded to foul up his entire electrical system until I rescued him. He was still using the switches and backfeeding his generator.

Sure let the smoke out...... Shocked
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« Reply #12 on: April 26, 2007, 10:03:34 PM »

If you do an electrically powered compressor I have a couple of suggestions since I tried it on my truck with a 1.5hp 120v motor, but gave up and belt drove it off the generator.  Only drive the compressor to about 900rpm, put a small fan facing the motor and compressor to further cool them.  I would use a receiver/dryer from Red Dot that has the trinary switch (three way switch) built into the top of it.  One switch is for low pressure cut out when you have to low of freon; the second is for medium high pressure to turn on the radiator fan (on a truck); the third is the high pressure cut out.  I wired mine so the compressor cut out when the radiator fan would come on, keeping the pressure in the system relatively low and the draw on the motor less.  Also I would suggest using a condenser that is twice the size suggested-also to keep the pressure in the system down and not overheat the motor.  It might work for you, but I was the most pleased with the compressor being driven off the generator directly.  Good Luck, TomC
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« Reply #13 on: April 27, 2007, 07:20:23 AM »

Some of the Onan 6.5's were not wired for 220 and only 120 with 2-breakers on the same leg. Something cheap about that deal.

I have an old ('80's model) low hours Onan 6.5 NH.  It can be set up for either 120 volt, 240 volt, or 120/240 volt.  There's a removable access panel that has a wiring diagram for each of the configurations.  I have mine wired for 50 amps @ 120 volts.  I have an auto transfer switch that will use the shore cord at 120/240 (both legs) or generator at 120 volts (connected so both legs are powered).  It works fine and I don't have to worry about load balancing, etc.  I'm sure a little research (google) can shed some light on the issue.  I found and downloaded a couple manuals for mine - a parts manual and a service manual in pdf format. 

David
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« Reply #14 on: April 27, 2007, 10:04:47 AM »

I will throw my support behind setting the generator up for straight 120 AC.

I have seen fascinating voltage drops and less than rated performance when trying to draw off one side.

And when you figure what percentage of your generator one air conditioner draws as it cycles through out the day, with the one on the other leg cycling to its own tune, balancing the loads is impossible.

And the spouse is not amused by all our fooling around and inane directives to operate things in certain orders...

I wonder if there is any measurable difference in heat build up in the gen head if it is run hard on one leg versus being loaded equally?

happy coaching!
buswarrior
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