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Old 07-18-2022, 04:48 PM   #1
Mini-Skoolie
 
Join Date: Nov 2021
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A/C Carrier MC-3 condenser stuck on with key out

Noticed the relay going to the larger skirt mounted condenser was smoking and melting. Took the key out, and the condenser fans wouldn't turn off. Unplugged the batteries and then the fuse.
That's for the A/C in the ceiling mounted unit in the back. The OEM dash A/C still kinda works, but will blow hot air intermittently.
Does this indicate a common problem in the compressor or water in the lines?
The bus sat in Nevada over the winter, freezing and dust are both very likely.
Looking at new condensers, they are crazy expensive! Is there a good DIY way to fix this?
Or if I do have to replace it, is there a better aftermarket cooling option?

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Old 07-18-2022, 05:09 PM   #2
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Year: 86
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lets start with your bus model and type.
and then talk about where your relay is/was and then we need to figure out the fuse that feeds the relay and where the relay is getting its command/control signal from?
do you have a seperate control knob for the rear A/C?
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Old 07-18-2022, 05:21 PM   #3
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and its probably your fan control relay.
that condensor runs your auxiliary unit and the dash?
i am assuming you have a van cutaway chassis.
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Old 07-18-2022, 07:31 PM   #4
Mini-Skoolie
 
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Quote:
Originally Posted by Jolly Roger bus 223 View Post
lets start with your bus model and type.
2006 Ford e450 Eldorado 15 passenger shuttle bus
Quote:
and then talk about where your relay is/was and then we need to figure out the fuse that feeds the relay and where the relay is getting its command/control signal from?
do you have a seperate control knob for the rear A/C?
Relay is inside on this janky panel by the passenger side door. I found the fuse that runs to it and pulled it out so it would stop smoking. Happened to have a new relay of the same kind to replace it, but I haven’t put the fuse back in cause I figure the issue is the condenser drawing too much.
There is a separate on/off switch and temp control for the rear AC. It was set to “off” and the key was out of the ignition, but the fans on the condenser wouldn’t turn off.
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Old 07-19-2022, 03:42 PM   #5
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the condensor itself doesnt draw any power the condensor fans do.
with this being said?
sounds like a bad switch or control relay.
cadillackid/christopher will see this and jump on here at some point.
i only know how mine was setup but its demoed now.
and the controls for the rear unit was ripped out before i bought the bus.
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Old 07-19-2022, 06:44 PM   #6
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Year: 1991
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yep its a stuck relay... really common on these.. should be a standard relay.. most often though when i find the relay contacts fuse together is when there are one or more bad fans that are pulling way more current than they should.. some dummy will often stick a bigger fuse in the fusebox which gets the system to run.. not realizing he may heat up the wiring and cause nice current arcs on the relay or a welding of the relay contacts because its over the relay current limit.. the relay board on carrier systems is usually labelled as to which does what.. I would definitely check all the fans when its running to see if they all run normally and if when its shut off they al spin down nice and freely.. if you have a clamp meter you can measure the total current of the condenser .. I have someplace the service manual to these systems.. carrier is most common system out there it seems on older busses
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Old 07-20-2022, 12:31 PM   #7
Mini-Skoolie
 
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here’s a pic of the melted relay. The fans all sounded good, and yes it did seem like just the fans were running. I’ve already replaced the relay but haven’t put the fuse back in yet in case the same thing happened again. I guess I can spray the fans with duster or something to make sure they’re clean? Is it safe to open up a bit and be sure there’s no short in the wiring?
I guess i’m wondering; if this is common, is it an issue with the relay getting too hot on an already hot day after a long drive and melting, thus creating an internal connection, or is it debris getting into the condenser and causing a short?
Thanks for all the insight!
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Old 07-20-2022, 01:03 PM   #8
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that looks like it melted because the contacts got dirty / corroded and you had an external Arc.. id seriously look at the contact on the board itself..
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