1989 temperature switch on Optional A/C system

[tmsnyder]

I recently swapped out my old crudded up 4 core brass radiator for a new aluminum replacement from RockAuto.  It fit fairly well, dimensions were all correct except the upper tranny cooler line was further up on the radiator, just needed a short extension to make that work.


It's also missing completely a port for a thermal switch which activates the twin electric fans in front of the radiator.  It's a pipe threaded plug, the chevy diagram says it closes to ground at 221F.


Any suggestions on where to relocate this?


One option I'm considering is to use the thermal switch on the passenger side head which when hot, it closes to ground and activates a warning light and beeper on the dash.   If they're both switching at 221F, then I could just use one switch to run both.  But I don't know, maybe that switch activates the warning light at higher than 221?  Anyone know?


Also, I'd like the fans to come on a little sooner than any warning light. 


Could also put a manual switch on the dash for the driver to turn on the fans whenever they want.


Anyone know at what temperature a 'high temp' idiot light comes on?

[Rickf1985]

Usually there is a blank plug in the thermostat housing or if there isn't you can get a housing with one. At that temp the thermostat would be wide open and full flowing so that would be a good time for the fans to come on.

[DaveVA78Chieftain]

Here are a few ideas
https://www.summitracing.com/search/part-type/fan-switches-thermal

[tmsnyder]

Thanks Dave.

Hi Rick, that was a good idea, I tried the thermostat housing fitting, it has a thermal vacuum switch in it leftover from the emissions system. Even with a 1-1/4" wrench on it, it wouldn't move and I didn't want to break the housing so I moved on. 


Definitely could just order an aftermarket one with the port I need, but instead found a port on the back side of the water pump that was unused.  Managed to get the switch installed there with a 3/8 to 1/2 NPT bushing.  Extended the wire a bit and all done.


I think that engine overheating warning light switch I mentioned earlier comes on at around 250F.   This fan switch comes on around 221F, so I could not have used the same switch for both uses, I'd either be listening to the buzzer way too frequently or the fans would come on way too late for an overheating motor. Neither would be a good scenario.

[Rickf1985]

If the buzzer comes on at 250 all it is telling you is to get out quick before the flames come through the dogbox!!! If it is that hot there is no water left and it WILL be lighting off shortly due to heat soak with no coolant. I don't know the specs but I am sure it is a lower temp than that.

[tmsnyder]

I know, right?   Too dang hot!   If I ever hear the alarm going off I'm headed to the side of the road b/c there's probably no coolant left in the head where that switch is located!  Warped head time most likely.


According to Prestone though 50/50 antifreeze and a 15psi radiator cap gets the boiling point to 265F, this jibes with where I see the redline on my vehicle gauges.