Hey,
Two problems, first the temp gauge goes where it wants(off position,9 o'clock,in the red)second, if I put the defrost on it blows out all the vents(except center console,which doesn't produce any air.)I checked the valve on the intake manifold and it has vacuum.I guess it's time to do open dash surgery.
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philvo

My '86 240 had an erratic temp guage. The cause was the temperature compensating board inside the instrument cluster, a common problem. The cluster needs to be removed and opened up and the board contacts (4) cleaned.

The other problem sounds like no vacuum to the heater buttons on the center console. Mine did that because of a split in the small rubber vacuum hose from the valve at the intake manifold to the vacuum reservoir under the dash. Once they start splitting, you need to replace the whole hose, easy job.

Jim,
What does the t.c.b.look like?I disected an '87 instrument cluster, but I don't know what I'm looking for.Is it behind the gauge itself?
I'll replace that vac hose with one out of my parts car.
Thanks, Phil
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philvo

Once you have the instrument cluster out, you remove the screws (6?) holding the back onto the front. When you separate these two, look just below the fuel and temp guages on the side of the main board which faces forward. The temp comp board is about 2 inches long, rectangular. Clean the pins by lightly scraping them. I use small dental tools. I also spray a little contact cleaner on a wire the size of the pins and run the wire through the 4 connectors on the temp comp board to clean them. I've had to do this twice on my '86 and '88 240s. While you have the cluster out, you can clean and tighten other electrical connections such as the guages and the voltage regulator.

thanks Jim,when it cools off here in Maine I'll give it a once over.I fixed the vent issue,the hose was pinched where it goes thru the firewall.
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philvo

Good for you on that vent problem! When you disconnect the instrument cluster be sure to write down what wire goes where. I forgot to do that once and had to think about it to get it back right. The PO of my '86 connected the instrument wrong and somehow burned out the speedo. The shop charged him about $200 to put in a used cluster!

I've had it out before to remove clock/install tach.I'm pretty sure I know what the temp comp board looks like as I 've got an instrument cluster out of an '87 apart on the bench for practice.It's about 2"x3/4" and has a bunch of diodes and resistors.I'll clean all the pins and contacts and see if any resoldering needs to be done and give it a try.Next is a prepump/sender transplant.
Thanks again, Phil
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philvo

Don,
Looks just like mine.. ie no board installed.. how does the board connectors attach to the main PCB?..soldered into the holes?... I do not think mine has any evidence of ever being soldered in.
Karl

I removed the temperature compensating board for the pictures.

The temp compensating board attaches to the main cluster PCB by four pins. I presume these are power, ground, signal in, signal out.

I've repaired several boards by resoldering the boards and cleaning and tightening the connectors (where it grips the pins).

But I've also repaired several other boards by replacing the integrated circuit and the transistor. I bought a bag of the ICs on eBay for a few bucks, so have a lifetime supply. However, in the past, I sent several of these ICs to another BB'er who was unsuccessful with his repair. So a bad IC is not always the reason for failure. (Even so, it only cost him $0 -- he had no reason to complain).

Others on the BB have described a means to bypass the temp compensating board. I've not tried this.
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Don Foster (near Cape Cod, MA)

Guys
Any idea why my cluster would not have the board in it? 86 245. I was chasing similar eratic temp guage readings, I found where the board should go (white plastic guides below temp and fuel guages) and the 4 holes in the main PCB but no board. Could it have been removed? do the guages work if you remove the TCB?
Karl