We will now begin to drill down further to another level so we can differentiate between the temperature control systems from a circuit perspective. This will allow us to start taking apart the two systems to get a better view of what is in stake.
First off, we will pull in both MTC and ATC circuits.
I’ve uploaded the pdf versions of them if you would like to have a cleaner diagram. They are at,
We will be using the ATC circuit diagram to mark up and denote the changes that will have to be made. But before we begin let us remove the right half of the diagram because it is exactly the same as the MTC and we will not be making any changes to that side anyway.
Now let us use some coloring to show the different parts of the circuit and what we have to deal with.
First off, those items in red can be wired in with simply tapping wires that are already in place.
• Thermo Control Amp – we can tap the original signal from the MTC side.
• Thermal Transmitter – we can tap the signal from the temperature gauge.
• Fresh vent motor – we can tap the signal from the pre-existing MTC side.
• Illumination - we can tap the signal from the pre-existing MTC side.
• Power – we will have to see where to get this unswitched power source from. But there are choices available.
From our initial assessment, those items in magenta will most likely stay in place. They are basically the motors. The wiring will have to be reworked somehow because there are some differences particularly with the feedback to the control unit from those motors.
• Air Mix Door Motor – the main issue is with the PBR. The ATC system uses +5VDC while the MTC use +12VDC.
• Mode Door Motor – the feedback switches are wired differently on both systems.
• Intake Door Motor – the ATC has two additional wires ??? We will have to come up with something here.
Update 3/15/2006: Confirmed that the motors will not need to be replaced after all!!! Also, the intake door motor does indeed have pinouts for two additional wires!!!!!!
Those items in blue will have to be purchased and added in.
• In-vehicle sensor (Part #: 27720-0E000 - $20.31)
• Sunload sensor (Part #: 27721-0E000 - $27.29)
• Ambient sensor (Part #: 27722-0E000 - $27.71 & mounting bracket 27715-0E000 - $5.23)
• Blower HI relay (Part #: 25230-79971 $12.10 w/ mounting bracket 25235-43L00 $1.64)
• Fan Control Amp (Part #: 27761-85E01 $57.25 w/ mounting bracket 27152-0E000 $6.20)
• Aspirator (Part #: 27726-0P000 - $5.00 & hose 27727-1E400 - $3.41) – not shown in the diagram because it is not an electrical component.
There you have it. It seems like, with the exception of those items that will need to be added in, a lot has to do with simply rewiring some stuff around. But the full truth will actually come once the work has begun.