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Author Topic: MCI over the road AC question? UPDATE  (Read 3877 times)
jmblake
Jason & Martha Blake
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« on: April 22, 2009, 05:58:37 PM »

My bus ac quit working on our last trip, the blower runs and the condenser fan works it seams to me that the compressor is not kicking in to cool the bus. The breakers in the bay are not tripped is there a relay somewhere that controls the compressor that could be bad. I think it has to be something electrical because it just quit all of a sudden. a\Any help would be appreciated thanks in advance Jason.
« Last Edit: May 20, 2009, 06:57:34 PM by jmblake » Logged

buswarrior
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« Reply #1 on: April 22, 2009, 07:35:43 PM »

Do you have any refrigerant left?

Check the sight glass on the little tank in the condenser compartment.

Better, put a set of AC gauges on it to see what's what.

Belts are still on? Any loose wires hanging around?

Check to see if you have any voltage at the various electrical connections on the compressor.

A set of AC gauges and some basic AC maintenance knowledge is critical to a busnut to maintain the coach AC at a reasonable cost.

happy coaching!
buswarrior

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junkman42
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« Reply #2 on: April 22, 2009, 08:19:08 PM »

My mc7 1971 vintage OTR decided to quit one fine day!  What happened is that the controller which is mounted under the floor between My driver and co pilots seat decided to give it up.  I managed to add a switch to bypass the controller and basically control the temperature by turning a toggle switch on and off.  If You need a copy of the mod if it is applicable to Your coach I will copy and send it to You.  Regards, John
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JohnEd
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« Reply #3 on: April 22, 2009, 09:05:41 PM »

You need the gauges to do most any trouble shooting.  You can't check the freon level with the sight glass if you can't get the compressor to engage.  You can't use the gauges either.  You need to determin if you have freon in the system.  there is a little pressure switch somewhere that detects a low freon condition.  If you developed a serious leak and all the freon ran out you would see that the compressor clutch wouldn't actuate when the system was turned on.  Find the low pressure switch, see if the contacts are closed.  You can jumper that switch and see if any pressure develops but you can only test that way for a short period of time because with no freon the compressor will burn up if allowed to run without oil.  You should see freon gushing past the sight glass in just a matter of moments.  Breaking a fitting open is also a test but there will remain some small amt of freon under pressure that might deceive you.

No freon would be my first guess.  Get a basics AC systems book....it ain't rocket science but that experience is critical.  Nick!!!

John
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« Reply #4 on: April 23, 2009, 03:37:34 AM »

This happen to me on my OTR, it just stopped one day in really hot weather. My compressor has a low pressure and high pressure switch located right on the compressor. You can jumper them out just to see if the compressor clutch engages which is what i did. My clutch was fine, it turned out that I had one loose fitting and a leaking hose connection where it is crimped. Tightened one and replace the other, now we are putting in new compressor head plates. Hopefully this will get my system back up and running again.
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jmblake
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« Reply #5 on: April 23, 2009, 04:06:20 AM »

Thanks guys, I just had the freon toped off before our trip that is why I thought it might be electrical or a relay some where. I'll keep diging. Thanks Jason
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PADoug
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« Reply #6 on: April 23, 2009, 12:08:42 PM »

 Embarrassed I know I don't qualify to answer this post, but just an outside shot: The MCI 9 that I was looking at today had a tag that stated very clearly that air pressure should be at 100PSI or it won't stay on. Funny, I was going to post this question as part of a new thread anyway.

So what does air pressure hae to do with OTR AC?

Doug
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bottomacher
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« Reply #7 on: April 23, 2009, 01:07:59 PM »

I don'k know if this the reason, but air pressure keeps the belt tensioner cylinder extended.
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jmblake
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« Reply #8 on: April 23, 2009, 01:52:09 PM »

Yes the air is over 100psi and it does keep the tension on the belt. I called MCI Tech today and they don't think its electrical, they said it may be air locked at the compressor for some unknown reason, they sudjested a AC specialist. I'll have to contact my local AC guy and see what he thinks. Jason
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Nick Badame Refrig/ACC
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« Reply #9 on: April 23, 2009, 04:10:41 PM »

Hi Jason,

Your system could have a High PSI cut out safty switch that has a manual reset.

Your system could have been overcharged causing it to trip. Look through your manual for the location of this safty.

Let us know
Nick-
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jmblake
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« Reply #10 on: April 23, 2009, 04:52:45 PM »

Hi Nick
 I don't have a manual yet, Where would i look for a reset switch? MCI Tech wasn't the friendlyest since I don't have a fleet of buses. Any help is appreciated. Thanks Jason
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« Reply #11 on: April 23, 2009, 05:33:38 PM »

Hi Nick
 I don't have a manual yet, Where would i look for a reset switch? MCI Tech wasn't the friendlyest since I don't have a fleet of buses. Any help is appreciated. Thanks Jason

MCI tech support has always been quite helpful to me.  They even employ some of the engineers who designed the Dina and I have talked to them.  Maybe I get better service because my bus is a 1995. 
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
bottomacher
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« Reply #12 on: April 23, 2009, 05:54:56 PM »

I have a copy of the Greyhound factory a/c training and installation/service manual for the MC9 hvac system that I am going to sell when I remove my chassis air. It is about 400 pages of accurate information, and it is THE manual for these systems. Email me at bottomacher@hotmail.com if interested, and I will post it on the classified section of this board.
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Nick Badame Refrig/ACC
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« Reply #13 on: April 23, 2009, 07:46:38 PM »

Hi Nick
 I don't have a manual yet, Where would i look for a reset switch? MCI Tech wasn't the friendlyest since I don't have a fleet of buses. Any help is appreciated. Thanks Jason

Hi Jason,

Well, it would only be between the compressor and the condencer coil and it would be the smaller diameter tube.
Look for some kind of "TEE" with a device that has wires connected to it.
When in doubt, jump it out!
Just remember, that psi switch tripped to save your compressor from failure.

Good Luck
Nick-
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« Reply #14 on: April 23, 2009, 08:11:03 PM »

Jason,

Whatever is wrong with your bus must be contagious. When we first bought our bus a year and a half ago the air was really, really cold and slowly last summer it started to be less and less cold. I pulled the filter this spring and it was covered in dog hair, so I figured when i cleaned it the air would work fine. No such luck. On a test drive yesterday it blew warm, almost hot air. I checked the sight glass in the condensor compartment and it shows halfway up the sight glass but that is with the engine off and on a healthy driveway incline with the bus nose downward.

Do you check the sight glass on flat ground with the engine running and the ac on???

My next question is, do we ever stop spending money on these things we call buses??

I need a good old healthy gambling addiction...  just kidding. I gripe but I love my bus and the freedom and joy it brings my family.

Good luck Jason and if you find the problem keep me informed and I will do so for you as well.

Rick
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