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Author Topic: MCI bus AC  (Read 4960 times)
Nick Badame Refrig/ACC
1989, MCI 102C3, 8V92T, HT740, 06' conversion FMCA# F-27317-S "Wife- 1969 Italian/German Style"
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« Reply #15 on: July 16, 2009, 02:54:21 PM »

Hi Paul,

Justin is correct! Your low side at 80deg outside ambient should be between 35 to 40 psi. Your high side should climb at the same rate when adding R-134A.

 Your hot water to the heater coils should be turned off... Make sure of that or you will effect the gauge readings.

When you get to 35 psi on the low side, start looking for a sweat back on the larger/suction line into the compressor. Add accordingly

until you feel the cold vapor/sweat on the pipe. At that point, your are there... Some systems that have been converted from R-12, to

R-134A  seem to change the atomization of the refrigerant and render the sight glasses useless. So, Don't go by the sight glass with a conversion system.

Being low on refrigerant will cause the low psi switch to short cycle the compressor, thus giving you intermittent cooling.

Good luck
Nick-
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paul102a3
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« Reply #16 on: July 16, 2009, 04:32:50 PM »

Justin or Nick,

If I understand correctly, you feel the system is low on 134 is that correct? If I bring the system up to the correct charge how does that affect the "on" light at the temp control switch on the dash?

The compressor is not cycling on and off at this time and stays energized so I assume the pressure is not low enough to trigger the clutch to disconnect. Is that correct?

Thanks for your help and education.

Paul
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2001 Prevost XL II
Nick Badame Refrig/ACC
1989, MCI 102C3, 8V92T, HT740, 06' conversion FMCA# F-27317-S "Wife- 1969 Italian/German Style"
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« Reply #17 on: July 16, 2009, 06:45:33 PM »

Hi Paul,

Yes, you still need more refrigerant.

The light on the dash comes on when the low psi switch openes. Your system may activate the unloaders instead of disinguaging the clutch.

Hope this clears up your concerns.
Nick-
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RJ
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« Reply #18 on: July 16, 2009, 10:08:58 PM »


One last thing, and I donít know how significant this may be, but the hot water system for the bus is shut off. I was reading an article that stated the hot water circuit should be on in order for the system to work correctly.



Paul -

I don't recall if MCI's system is similar to GMCs (I think it is), but with a Jimmy, the HEATER actually controls the temp output of the AC system.  Might try turning your hot water systen back on and see what happens.

FWIW & HTH. . .

 Wink
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RJ Long
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« Reply #19 on: July 17, 2009, 03:55:42 AM »

Paul,

Send Doug (Doug1968) a message, he told me once that a valve has to be on in order for it to work. Not sure where it is though. It might be the same one RJ is referring to.

Paul
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« Reply #20 on: July 17, 2009, 04:40:26 AM »

RJ, You are correct, the heating circuit does need to be on to control the temperature inside the bus and I was not aware of this until a few days ago. That was my reason for questioning if this could have caused any damage. At least I now know it why it was so cold in the bus when the AC was working.

I am sure there is a reason but it seems odd that that you would ADD heat to the incoming cold air to adjust the temp rather than cycle the compressor.

Paul, I did send Doug an email yesterday but have not heard back as yet.

I will try to get my friend out here in the next few days to try and add more freon as both Nick and Justin have suggested. My thanks to Nick for the sight glass tip. As we were adding the freon yesterday , we kept checking the sight glass and there were no changes so we stopped.


Paul
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Nick Badame Refrig/ACC
1989, MCI 102C3, 8V92T, HT740, 06' conversion FMCA# F-27317-S "Wife- 1969 Italian/German Style"
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« Reply #21 on: July 17, 2009, 05:26:48 AM »

Hi Paul,

On my MCI 102C3, I leave the heat controls next to my seat on all the time. In summer time, I shut the main heat valve off at the engine

because several times in the past, I had hot water flowing when the A/C was on.... Not good! Maybe another problem but, I just assume

not having water flowing there.

Nick-

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justin25taylor
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« Reply #22 on: July 17, 2009, 04:30:54 PM »

My understanding of the reason you "add heat instead of cycling the compressor" is as long as the compressor is running the evaporator coil stays cold and removes moisture from the air (think water dripping under bus). If you cycled the compressor the humidity in the coach could get high causing folks to feel hot even thought the air temperature is correct.
Think about our coaches original design and 47 people on the bus talking, breathing, etc and how much moisture they add to the air.

I leave my water valves open for that reason I can't stand humidity. With the warm air mixing with the cold you get the temperature you want, keep the air moving, and keep the humidity down.

I understand I am going overboard but I hope this helps anyone who was wondering why.

Best,
Justin
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Doug1968
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« Reply #23 on: July 17, 2009, 05:06:47 PM »

Paul - Justin - Nick,

I have a friend with a 102A3 and during a conversation with him @ Bus N USA he told me that his OTR air conditioner would not work well unless he shut off the engine coolant return valve. This is the valve inside the R/H access panel at the back of the bus.

This is just as Nick is stating I believe.

Paul,

I just got your e-mail this afternoon and I plan on responding to you later this evening.

Doug

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1986 MCI 102A3 - 8V92 - 5 speed
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Nick Badame Refrig/ACC
1989, MCI 102C3, 8V92T, HT740, 06' conversion FMCA# F-27317-S "Wife- 1969 Italian/German Style"
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« Reply #24 on: July 17, 2009, 09:03:33 PM »

My understanding of the reason you "add heat instead of cycling the compressor" is as long as the compressor is running the evaporator coil stays cold and removes moisture from the air (think water dripping under bus). If you cycled the compressor the humidity in the coach could get high causing folks to feel hot even thought the air temperature is correct.
Think about our coaches original design and 47 people on the bus talking, breathing, etc and how much moisture they add to the air.

I leave my water valves open for that reason I can't stand humidity. With the warm air mixing with the cold you get the temperature you want, keep the air moving, and keep the humidity down.

I understand I am going overboard but I hope this helps anyone who was wondering why.

Best,
Justin

Hi Justin,

Any A/C system is a Dehumidifer.. Any dry heat system that produces temps above 120 deg's, is also a dehumidifer.
No need or reason at all to mix them!

Nick-
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justin25taylor
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« Reply #25 on: July 17, 2009, 09:33:35 PM »

I learn something every day here. Thats why I enjoy reading this great forum.

In Texas, after a rain especially when I used to keep my water valves closed in the summer and the compressor unloaded (turned off) because the thermostat was satisfied the humidity would rise. Then when the compressor came back on it would drop. Sometimes on a mild, but humid, sticky day I would get fog on the inside of my windshield.

When the valves are open so the a/c and heat blend I never have this trouble. The compressor will pretty much stay loaded (on) and the heat added will keep a nice even dry temperature throughout the coach.

My Ford Expedition works the same way: When you turn the climate control to auto, the compressor cycles anytime the ambient temperature is above 45 or so. It has a "blend door actuator" (that was a pain to replace) that allows warm air via the heater core to mix with the cold air coming off the evap coil. That way the temperature is easily regulated. So even though it can be wasteful by running the compressor when you don't have to have it it sure feels more comfotable to me.

My old bus 05 Eagle had a little problem regulating the temperature when I first bought it. It would blow ice cold then blow way too warm, back and forth. I replaced the valve that regulates the water to the heater core and bam problem solved.

So, The two things I learned is I am way more sensitive to humidity than most people and I should close the water valves on my bus.

Thanks, Nick for the info and I am sorry if I mislead anyone.
Best,
Justin

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RJ
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« Reply #26 on: July 18, 2009, 03:11:33 PM »


So, The two things I learned is I am way more sensitive to humidity than most people and I should close the water valves on my bus.



Justin (and others) -

I'm going to respectfully disagree with Nick regarding closing the hot water valves on an OEM factory OTR A/C system, at least on a GMC. 

And for those with other brands still running the factory HVAC OTR system, be they MCI, Eagle, Prevost, Setra, etc., might I suggest that you get out your Maintenance (Shop) Manual and thoroughly read through the HVAC section, especially the part where it talks about the system's design & operation.

Sometimes it pays to read "Da Book" first to understand why the factory does things the way they do.  Once you understand, then you can make correct decisions for YOUR application.

FWIW & HTH. . .

 Wink
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RJ Long
PD4106-2784 No More
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Nick Badame Refrig/ACC
1989, MCI 102C3, 8V92T, HT740, 06' conversion FMCA# F-27317-S "Wife- 1969 Italian/German Style"
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« Reply #27 on: July 18, 2009, 03:38:36 PM »

Hi RJ,

No Problem..   The only difference between Da Book and the way we use our coaches is about 45 less humans exhaling humidity into the coach.. Wink

Otherwise, your eating up horsepower with the compressor running fulltime! The A/C system in out coaches is a bit overkill for us but, it does pass

the air a bit fast through the evaporator coil for proper dehumidification. For us, it works perfectly with very low humidity because of usually only 4 or 5

onboard.

Nick-
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« Reply #28 on: July 18, 2009, 08:17:25 PM »

If you are running a stock HVAC, you are sucking in a fair bit of fresh outside air, which needs conditioning.

I'll stick with MCI, leave the water valves open and leave the temp controls to regulate what goes on.

As noted, you will fog up under the right conditions with the water valves closed.

Why mess with perfection?

happy coaching!
buswarrior

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