Hello All
I have a MCI 102c3 that I am converting. I am just starting my conversion. I removed the stainless registers at the floor. After removing the registers I started the bus to move it and I noticed the thermostat on the dash read -40. I think I might have removed the cabin temp sensor. Can someone advise me as to where this sensor is or how to replace it. Thanks
mine was on the driver side at the rear drive tires above the floor near the cold air return vents
dave
Do you know what it looked like or do you know where i can get a new sensor? Thanks
Jared
Quote from: sledhead on April 21, 2018, 04:25:00 AM
mine was on the driver side at the rear drive tires above the floor near the cold air return vents
dave
Does anyone know what this sensor is or what it might look like? I found what I believe to be the wire for the cabin thermostat but not the sensor itself. Please help me figure this out. THanks
The sensor in an old MC8 had 4 wires attached to it, mounted in the air flow, inside the piping... oh geez... somewhere... maybe a piece of panel came off to expose it?
Long time ago since I had to think about it.
Isn't it in Da Book???
Happy coaching!
buswarrior
The book shows the sensor but dosen't show the thermal coupler in the vent. Nor does it show the part number or which wires to wire in a new thermal coupler. The book is basically useless in regards to how the thermostat gets it's single.
Quote from: buswarrior on April 25, 2018, 03:38:21 PM
The sensor in an old MC8 had 4 wires attached to it, mounted in the air flow, inside the piping... oh geez... somewhere... maybe a piece of panel came off to expose it?
Long time ago since I had to think about it.
Isn't it in Da Book???
Happy coaching!
buswarrior
Mine had a miltery spec style connector, the ones with a screw down collar to lock the plug in place. Was about half back on the driver side near the floor. 1994 MC-12
Sent from my ONEPLUS A5010 using Tapatalk
Ah... it was a Carrier system...
I've always wondered if there was an obscure separate vendor manual back then...
Happy coaching!
Buswarrior
I have the sensor that broke off but it dosen't have a number on it. Does your book have a part number for the thermal coupler? Thanks
Jared
Quote from: buswarrior on April 25, 2018, 03:38:21 PM
The sensor in an old MC8 had 4 wires attached to it, mounted in the air flow, inside the piping... oh geez... somewhere... maybe a piece of panel came off to expose it?
Long time ago since I had to think about it.
Isn't it in Da Book???
Happy coaching!
buswarrior
My books are all packed up and remote to my location.
Anyone else have the book or a part number?
Happy coaching!
Buswarrior
You can download parts and service manuals from mci now. I can't remember exactly where but I believe if you go to mcicoach.com tgere is a link at the top of the page that will take you to support documents or manuals or something like that, then select your series etc. Etc.
Sent from my SM-G930T using Tapatalk
Does anyone have any idea where I can find a replacement temp probe? My parts manual dosen't have the part listed. It's the little probe that goes in the drivers side stainless duct. THe one that tells the thermostat the ambient temp. Any help would be greatly appreciated. Even if you have a manual that contains a part number that would be great. Or a idea of how to retrofit some other type of probe. Thanks
Quote from: Jcparmley on May 18, 2018, 05:33:07 PM
Does anyone have any idea where I can find a replacement temp probe? My parts manual dosen't have the part listed. It's the little probe that goes in the drivers side stainless duct. THe one that tells the thermostat the ambient temp. Any help would be greatly appreciated. Even if you have a manual that contains a part number that would be great. Or a idea of how to retrofit some other type of probe. Thanks
to feed a relay...??????? ???
https://smile.amazon.com/gp/product/B00V4TJR00/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 (https://smile.amazon.com/gp/product/B00V4TJR00/ref=oh_aui_search_detailpage?ie=UTF8&psc=1)
Hi Buswarrior
What would I call the "sensor probe" in the intake duct if I was to do a search on mcicoach.com? Thanks
Quote from: buswarrior on April 26, 2018, 06:23:34 AM
Ah... it was a Carrier system...
I've always wondered if there was an obscure separate vendor manual back then...
Happy coaching!
Buswarrior
Perfect timing, for a brief moment, I am where the books are!
"Sensing unit - coach temperature"
Fwiw, the MC8 part number was 16B-10-33 and is listed in the "heating and air conditioning" section 16 of the parts manual, under "miscellaneous valves, switches, heat and A/C control components"
Just to get some of the wording familiar.
Happy coaching!
Buswarrior
And in the MC8 maintenance manual, the sensor lived in 2 different places during this model run.
One accessible inside the coach through the heater duct at the floor, RH side #2 panel, and underneath in the LH #1 luggage bay, in the center control duct.
You need to be suspicious of the 102C models, there were big changes over the top of them, there is likely more than external appearance differences as the 4 stroke engines came onboard, and the HVAC systems continued to evolve.
In all things busnut, Da Books that have all the revisions for your unit number are critical to speeding the job!
Happy coaching!
Buswarrior
Thank you so very much
.quote author=buswarrior link=topic=32976.msg376190#msg376190 date=1526730322]
And in the MC8 maintenance manual, the sensor lived in 2 different places during this model run.
One accessible inside the coach through the heater duct at the floor, RH side #2 panel, and underneath in the LH #1 luggage bay, in the center control duct.
You need to be suspicious of the 102C models, there were big changes over the top of them, there is likely more than external appearance differences as the 4 stroke engines came onboard, and the HVAC systems continued to evolve.
In all things busnut, Da Books that have all the revisions for your unit number are critical to speeding the job!
Happy coaching!
Buswarrior
[/quote]
Ok, so I now have the new thermocoupler and I wired it where the old one was. Now the thermostat says 138 rather than -40. I thought perhaps it was set for Celsius or something like that but I can't figure out how to change it. Any suggestions? Thanks
Quote from: buswarrior on May 19, 2018, 04:45:22 AM
And in the MC8 maintenance manual, the sensor lived in 2 different places during this model run.
One accessible inside the coach through the heater duct at the floor, RH side #2 panel, and underneath in the LH #1 luggage bay, in the center control duct.
You need to be suspicious of the 102C models, there were big changes over the top of them, there is likely more than external appearance differences as the 4 stroke engines came onboard, and the HVAC systems continued to evolve.
In all things busnut, Da Books that have all the revisions for your unit number are critical to speeding the job!
Happy coaching!
Buswarrior
Does anyone know why my thermostat says 138 degrees after I installed a new thermal coupler?
Mismatched parts, or the unit is defective.
In fleet use, used to see a lot of changed out units for controlling the coach temperature back then, and that was in a first line fleet...
Don't care what the display reads, what does it do to the coach temperature? Numbers displayed are meaningless, set the temp comfortable, and whatever the display says, that's your setting.
Coach up to temp, see if it will cycle the valve that feeds the heater core.
Happy coaching!
Buswarrior
Here is the schematic for a post 1993 102A3 with the 65 stud junction box which I believe you have:
Group 6 Page A-2
I am watching this with interest, I have a 1989 96A3, the display on my dash also reads -40.
Before demolition the OTR Air worked, not now, everything seems to be in order, plenty of refrigerant, compressor engages, no cold air.
While I had the floor out I noticed (and tripped over a few times) a wire that leads up the central duct to what I believe is a thermal sensor. This sensor can also be accessed under a plate from the front driver's side bay.
In the top picture you can see where the wire runs from the central duct into the side.
In the bottom picture you can see where the access plate is for the sensor above the generator.
I will be looking at this over the weekend to see if I accidently pulled the wires loose or otherwise damaged it while the floor was up.
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fwww.peterbylt.com%2Fmci96a3%2Ftempsense1.jpg&hash=37abeb7a074265baaece5e24549f307d57bf9460)
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fwww.peterbylt.com%2Fmci96a3%2Ftempsense2.jpg&hash=8d1bed5276122a938ab96b9e5081f1e823ab0762)
Peter
That's what happened with me. Everything worked fine before I began the tear out. When I tore out the stainless duck I broke the thermal coupler. So I purchased a new thermal coupler, installed it and now my temp reading is -40. I will try to turn the heat on and see if it responds. If it does, then perhaps I won't worry about it.
Quote from: peterbylt on October 05, 2018, 07:58:37 AM
I am watching this with interest, I have a 1989 96A3, the display on my dash also reads -40.
Before demolition the OTR Air worked, not now, everything seems to be in order, plenty of refrigerant, compressor engages, no cold air.
While I had the floor out I noticed (and tripped over a few times) a wire that leads up the central duct to what I believe is a thermal sensor. This sensor can also be accessed under a plate from the front driver's side bay.
In the top picture you can see where the wire runs from the central duct into the side.
In the bottom picture you can see where the access plate is for the sensor above the generator.
I will be looking at this over the weekend to see if I accidently pulled the wires loose or otherwise damaged it while the floor was up.
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fwww.peterbylt.com%2Fmci96a3%2Ftempsense1.jpg&hash=37abeb7a074265baaece5e24549f307d57bf9460)
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fwww.peterbylt.com%2Fmci96a3%2Ftempsense2.jpg&hash=8d1bed5276122a938ab96b9e5081f1e823ab0762)
Peter
The schematic shows a thermal coupler in the heat duct in the cabin (I replaced that) then it shows one also in the center control duct. I opened up the center control duck and there is no thermal coupler in there. It looks like the PO messed with it and rigged something up. I would post a pic but photobucket isn't working and I don't know of another app to post pics.
Quote from: jraynor on October 04, 2018, 01:05:08 PM
Here is the schematic for a post 1993 102A3 with the 65 stud junction box which I believe you have:
Group 6 Page A-2
Quote from: Jcparmley on October 05, 2018, 02:39:47 PM
I would post a pic but photobucket isn't working and I don't know of another app to post pics.
Look below thisthe dialogue pad and there is a BOLD ATTACH.
clic it and choose the photo from your puter...
It will appear :)
Here is a pic of the wiring inside the first bay center tunnel.
Here is a pic of the thermostat.
Hi Peterbylt
Did you ever figure out why your dash read -40? The snow is finally melting and I am looking forward to getting back into the bus to figure this out. Thanks
Quote from: peterbylt on October 05, 2018, 07:58:37 AM
I am watching this with interest, I have a 1989 96A3, the display on my dash also reads -40.
Before demolition the OTR Air worked, not now, everything seems to be in order, plenty of refrigerant, compressor engages, no cold air.
While I had the floor out I noticed (and tripped over a few times) a wire that leads up the central duct to what I believe is a thermal sensor. This sensor can also be accessed under a plate from the front driver's side bay.
In the top picture you can see where the wire runs from the central duct into the side.
In the bottom picture you can see where the access plate is for the sensor above the generator.
I will be looking at this over the weekend to see if I accidently pulled the wires loose or otherwise damaged it while the floor was up.
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fwww.peterbylt.com%2Fmci96a3%2Ftempsense1.jpg&hash=37abeb7a074265baaece5e24549f307d57bf9460)
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fwww.peterbylt.com%2Fmci96a3%2Ftempsense2.jpg&hash=8d1bed5276122a938ab96b9e5081f1e823ab0762)
Peter
When you say thermo coupler, are you really talking about a thermocouple? That should be the type of sensor used by that sort of temperature controller. Thermocouples are a little different from regular wiring. The thermocouple itself is made from two dissimilar wires welded together to create a junction. Usually one wire is copper and the other may be iron or nickel. The two most common types are "J" and "K" types, they have different temperature ranges but there are also some others. The thermocouple generates a very small current across the junction from the temperature difference from the tip on down the wires. This current is so small that even a small problem in the wiring will throw off the calibration. What most people don't realize is that you have to use the same wire that the thermocouple is made from all the way from there back to the controller. Every place that you have a joint there is the potential for another junction not much different from the one at the tip of the thermocouple and adding in any other metal can throw things off even further. So for instance, splicing in copper wires or using common butt connectors is a sure way to throw it all off. You can buy special plugs designed especially for connecting K or J type thermocouple wires and that is about the easiest and surest way to make your connections. Thermocouple wire is not particularly expensive and can be used to make the thermocouples as well. Widely used in industrial controls (which the MCI temp controller appears to be) and in science labs, they are a simple, reliable and highly accurate device.
Jim
Thanks Jim, that is helpful. What I am trying to figure out is why everything worked fine before I pulled out the duct. I broke the original thermocouple and purchased a new one from MCI. However when I plugged it back into the "socket" it read -40. When I went down into the front bay and plugged it into the "socket" in the main tunnel it read 138 degrees. It's all very confusing. What are your thoughts?
Quote from: Jim Blackwood on March 30, 2019, 10:25:43 PM
When you say thermo coupler, are you really talking about a thermocouple? That should be the type of sensor used by that sort of temperature controller. Thermocouples are a little different from regular wiring. The thermocouple itself is made from two dissimilar wires welded together to create a junction. Usually one wire is copper and the other may be iron or nickel. The two most common types are "J" and "K" types, they have different temperature ranges but there are also some others. The thermocouple generates a very small current across the junction from the temperature difference from the tip on down the wires. This current is so small that even a small problem in the wiring will throw off the calibration. What most people don't realize is that you have to use the same wire that the thermocouple is made from all the way from there back to the controller. Every place that you have a joint there is the potential for another junction not much different from the one at the tip of the thermocouple and adding in any other metal can throw things off even further. So for instance, splicing in copper wires or using common butt connectors is a sure way to throw it all off. You can buy special plugs designed especially for connecting K or J type thermocouple wires and that is about the easiest and surest way to make your connections. Thermocouple wire is not particularly expensive and can be used to make the thermocouples as well. Widely used in industrial controls (which the MCI temp controller appears to be) and in science labs, they are a simple, reliable and highly accurate device.
Jim
You tore out the interior and the ducting.
You didn't do any of that gently.
the wiring has been jerked, all bets are off.
Did you cut the cable before or after the disconnect plug?
Was there a resistor taped into the sensor bundle wiring?
How many wires ran to the temp sensor that was installed?
Does the sensor version match the control version?
"D" model buses had several variations of controls retrofitted and re-developed, because they failed regularly. Even after-market ones were out there.
The first line carriers were changing these things out like mad, before the coach even made 8 years old... there's no telling what the lower tier operators did after that.
In some matters, the books for the bus aren't going to help when the bus doesn't match anymore.
It might be easier to design a fix and add it in, than trying to work backwards?
The displayed numbers don't mean anything anyway. Yeah, I know, that'll make some generations heads spin, just ignore the damned numbers after a lifetime of counting on them...
Can you get the interior to a controlled comfortable temperature by making small adjustments to the control and wait for the resulting change in performance?
happy coaching!
buswarrior
That's all very good points. I guess the numbers don't really matter for me. But try to explain that to my wife!! The idea of making a new system work rather than working backwards is also a very good point. All of this is moot anyway if the OTR system is removed. At the moment it dosen't work. I have read so many posts about wether to keep the OTR or remove it. Some say to get it working and others say it's not worth the cost to maintain especially if you aren't going to use the bus but for some weekends each year. I am seriously considering taking out the OTR AC and just leaving the heat/defrost function or the OTR. If that's the case then the numbers on the controller is even less important as long as I can turn the system on and produce heat. I haven't had the ability to test the heat yet.
JC, unfortunately I can't offer MCI specific advice but I do know these devices well from industrial use. If we could just make the assumption that MCI followed industry best practices it'd make things fairly easy but unfortunately we have seen that they may not have always done that. So bearing that in mind, and also considering that I have not yet been into the sensor side of my climate controls please take this in the spirit in which it is offered which is to say advisory but otherwise YOYO.
Good chance we can expect the connectors MCI used to be thermocouple approved, that is to say that they will not change the very small current generated by the thermocouple in any way. If the temp you are reading is abnormally high it is an indication of either a mismatch or a calibration error. Normally you would not have any resistors in the circuit as that would just degrade the signal.
If I recall correctly, the thermocouple requires a fairly specialized sort of balanced bridge circuit which is sensitive enough to tell if microcurrents are being generated and in which direction. Standard practice is to run single strand paired thermocouple wire but in a bus you might find stranded. So in your case what I'd do first is take the new thermocouple and see if I couldn't find a way to connect it directly to the back of the controller, or as directly as is practical and see what your readings are. Odds are good that you've damaged the wiring somewhere and this should give a proper reading, allowing you to track down the problem. Avoid using jumper wires to make your connections if at all possible other than to hold a couple of wires in contact with each other.
If it still reads high then I'd question the new thermocouple as possibly being the wrong type. If you have the remains of the old one and the junction at the tip is still intact you can still use that to double check, it doesn't make any difference how long the wires are.
Now, each type of thermocouple uses a distinctive wire cover. Most common (K type I think but it could be J) is brown with a black stripe woven through it, then one wire has red insulation and the other has white. These are woven heat resistant insulations. See if your new part uses the same colors as your old one, if not, there's your problem.
Jim
Well hello there everyone!
I have missed you all.
FWIW...the book for the MC8 has a split year for locating those sensors, and not a lot of detailed information. Mine was on the passenger side sitting on the floor.
But...would that particular sensor cause a -40 reading on the dash?
I know the buses are different, but I figured it can't hurt to ask.
And my 2 cents on the OTR air: Keep it! I have found it to be worth it's weight in gold when driving in the summer, into the sun whilst getting sunburn.
8)
Quote from: Jcparmley on March 30, 2019, 04:13:38 PM
Hi Peterbylt
Did you ever figure out why your dash read -40? The snow is finally melting and I am looking forward to getting back into the bus to figure this out. Thanks
I have not got it to work yet, What I have done so far.
I pulled the sensor mount out of the top of the first bay (shown in picture) only to find just the holder, no sensor.
Contacted Luke, who tracked one of the sensors down for me (expensive little buggers!)
I installed the sensor into the holder and reinstalled it into the Duct.
End result, no change still reads -40 .......
Peter
Pete, have you tried hooking it up backwards? (Can't hurt it by doing that.)
I'll be hooking up an Omega controller in a couple days so I need to review the books anyway. The thermocouple colors are:
J= red and white (2nd most common)
K= red/yellow (most common)
T= red/blue
E= red/purple
N= red/brown
R=red/black
S=red/black
B= red/black
So most of these you can differentiate by the wire insulation color. The red is always the (-) terminal.
Jim
Quote from: Jim Blackwood on April 02, 2019, 06:17:23 PM
Pete, have you tried hooking it up backwards? (Can't hurt it by doing that.)
I'll be hooking up an Omega controller in a couple days so I need to review the books anyway. The thermocouple colors are:
J= red and white (2nd most common)
K= red/yellow (most common)
T= red/blue
E= red/purple
N= red/brown
R=red/black
S=red/black
B= red/black
So most of these you can differentiate by the wire insulation color. The red is always the (-) terminal.
Jim
So, I went back in and checked to see if I had installed the sensor reversed as suggested, Found you could only install it one way, wide and narrow connectors.
The wire is a "J" red and white.
I traced the thermocouple wire back up to the dashboard where the display/controller is.
This is where it gets interesting, I found the other end of the thermocouple wire, with special connector, not connected to anything and no place to connect it into the display/controller.
I examined the controller and current wiring, all look to be nice tagged MCI wiring, I cross-referenced with the MCI wiring diagrams, It looks like my bus has the AC wiring and controllers of a three year older 96A3 that uses a different type of cabin sensor.
That is why the sensor was missing.
To further complicate the matter, when I purchased the Bus it had a Welch Industries Auxiliary air conditioner in the back that I removed, that is probably when the problems started, the Air Conditioning worked great on the initial ride home before I started tearing things apart.
I did not run the bus for at least a year after I purchased it while I did a lot of the heavy conversion work.
I now believe Welch changed out the controller and some of the wiring to conform to wiring they had for the Auxiliary air conditioner they installed.
I now have to figure out what Welch used for a cabin temperature sensor, and any other changes they may have made, I would currently settle for bypassing the temp control and running the AC full on, controlling the temperature with the on off switch.
Peter
You can get small and relatively simple temperature controllers on ebay for about 10-15 bucks, or more complex and complicated ones for about 25, both of which can use thermocouple inputs.
Jim