OTR Thermostat

[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

[Jcparmley]

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]

[Jcparmley]

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

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

[Jcparmley]

Does anyone know why my thermostat says 138 degrees after I installed a new thermal coupler?

[buswarrior]

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

[jraynor]

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

[peterbylt]

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.








Peter

[Jcparmley]

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.

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.








Peter

[Jcparmley]

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.

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

[eagle19952]

  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

[Jcparmley]

Here is a pic of the wiring inside the first bay center tunnel.

[Jcparmley]

Here is a pic of the thermostat.

[Jcparmley]

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 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.








Peter

[Jim Blackwood]

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

[Jcparmley]

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?

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