Strange sensor (?) on head, 73 small block

[tom3]

Getting started on an engine project, wondering what this sender is for. Just curious, never seen this one. On the head in an accessory bolt hole. Can't figure what this would sense or control. Anyone know? 400 small block out of a Caprice I think.

 

[rchydzik]

I believe it is a temperature sensor in the DC supply line to the AC compressor. It prevents the AC compressor from running on a cold engine.

 

[sandlapper]

WAG perhaps bubba thought it might signal his temp gage/lite? Or trigger the AC-on idle speed solenoid on carb? Regardless, doubt that'll help much.

g'luck on your 400 project Tom! which cast code block is it?

Don't scrap its short rods; someone on fleabay or craigslist may want em.

 

[DougD]

I believe it is a temperature sensor in the DC supply line to the AC compressor. It prevents the AC compressor from running on a cold engine.

We have a winner.

 

[tom3]

g'luck on your 400 project Tom! which cast code block is it?

Don't scrap its short rods; someone on fleabay or craigslist may want em.

Had this back in the corner for 20 years, finally got some time to play with it. Going to rebuild shortblock as stock, small cam, good heads, 4 bbl, exhaust. See what a mild 400 will do compared to a similar 350 thats in the 70 now.

Poor old small block was really neglected looks like. Got some work ahead, cylinders look real good so far.

 

[80Zcorn]

Good luck!

 

[ChevyReb]

Should not be any rust in that block...that's a good undercoating job!

511 block is it a 4 bolt main? I think those came both 2 or 4 bolt iirc.

Most people say best is 509, then 511, and 817 is preferred order best to not best.

 

[tom3]

It's a two bolt main, three core plugs on side. Still has plastic timing gear, or what's left of it. Kind of surprised that the head chambers and piston tops have very little carbon build up, stock bore, doubt it's been apart.

 

[FS87LT]

On many small blocks, there was a "metal sensor" on the rr of the rh cyl head, to take over from the normal heat temp sensor in the cyl head (coolant temp) so the gauge would read more accurately at higher temps. An old-line Chevy service manager told me that when I asked about that sensor on my '77 Camaro 305.

A/C compressor normally ran in the Defrost mode, to minimize fogging of the inner windshield initially. In that particular vehicle application, not sure if the metal temp sensor was on the front of the motor, adjacent to the normal sending unit, but it could have been. As a way to save money on wiring?

Happy Holidays!
FS87LT

 

[tom3]

Got out the multimeter and checked out the sensor. It was open circuit at about 40 degrees, then closed at something over 80 degrees which looks about right to control the compressor. I suspect GM didn't that big hoss A6 compressor running at low temps for some reason?