Thread: Thermos, A/c and temp senders....

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Could some one please help me with a huge favour, at the moment i am struggling with a wiring problem im having.......

I have a thermo fan installed on my car as the only sourse of cooling it has a temperature sending (Derale) unit to automatically turn on as well as a manual override switch however it also needs to tie in with the 3 speed A/C unit (5pin switch) i have installed......

I would like the thermo to have 1 relay, the A/C unit to have 1 relay only and only energise when the switch is turned on and the temp sender already has an inbuilt relay.... Would someone out there be able to do me a HUGE favour and work out a wiring diagram???

Thanks in advance!!

You will need to determine the hot wire to turn on the a/c and use that to trigger the fan to come on using the relay.....

The relay for the fan itself can use the same power wire as the other 2 relays.

The manual overide relay and all the others should be located close together as to minimize the wire distance and resistance.

Basically a hot wire of the proper guage to the first relay and then another short power wire of the same guage to the next one and then to the next one as the relays have power at all times, they only complete the circut when the switch wire gives the signal.
Each relay will need a seperate trigger/switch wire...one coming from the manual overide to one relay, one from the thermostat and one from the a/c compressor......

A good volt meter should help you find which wire is energized to the compressor when turned on.Use this wire to the switched connection on your relay.

Make shure to ground everything good also...A little dielectric grease goes a long way to help with all connections and prevent corosion too.

Hopefully this helps a little......

This should allow the fan to stay off untill the thermostat tells it to run or the manual switch is flipped or the compressor comes on.......usually the fan runs continuously when the a/c is on in most applications to help cool the a/c refridgerent temps rather than cool the radiator of the engine...this helps to keep the a/c cool inside during idle and low speeds.

I would also calculate the fans total amps and use a inline fuse on the hot wire powering all the relays..........or use the wire size you determine and use the appropiate fuse size...preferably a blade fuse...they make some nice ones with rubber around them and a little flap to sort of seal the fuse from weather.....I used a 50 amp one from a stereo shop and some pretty heavy wire for a high end stereo set up.

Also you can use the same outputs of the relays to power the fan..connect the main power feed from the fan to one of the relays and jumper the relays outputs from one to another.......this will allow the system to work automatically........I would not recomend having a main switch to activate all of these relays...........if you forget to turn the main overheating and engine death are likely.

The way I have described will allow all of the systems to work in unison and this is the recomended way..........In my opinion having a main on button to activate all of these systems is a race only deal....have heard many people forget to turn on fan power when it has a main to activate it....too many distractions on a street car to remember to turn the fan on everytime....sooner or later it will get forgotten...

Great advice, shawnlee.

Here's how I always wire radiator fans:



I would recommend using a trinary switch on the AC high pressure line to control the fan rather than just having it come on whenever the AC is on, or whenever the compressor is running.

If you already have a binary switch to keep the compressor from running if the pressure is too high or too low (most systems do, and all should), then the simplest way to do what you want is to replace the binary switch with a trinary switch. The compressor section of the trinary switch will be wired to the same wires as the binary. The additional two wires on the trinary switch (the fan section of the switch) can simply be wired in parallel with your over-ride switch...assuming that in your case the over-ride switch trips the relay in the thermo switch instead of bypassing it. Otherwise kindly disregard this paragraph, and use the trinary switch fan section to trigger your new fan (AC) relay.

Sorry I'm not familiar with the integrated switch/relay you speak of. I typically just install an OEM radiator fan switch (Standard Ignition TS-87) in the lower radiator tank and wire it per the above diagram.

Hope this helps....

Excellent diagram.......I learned something new.

Never thought about triggering everything from before the 86 terminal tied together like that......Makes for less wires under the hood and I am all for that!

Thank you.

Thanks, Shawn, and your welcome.

FATNLO,
I was just looking at the Derale Performance website. Looks like they offer a wide variety of fan controllers. They don't however, offer any wiring diagrams or installation instructions for download on their site which makes it difficult for me to work out an exact diagram for you.

What model fan controller do you have?

Thanks boys for your help so far, i really appreciate it like you wouldnt believe :-)
Im trying to teach myself how to do this wiring and so far this is the only hurdle i have had....
I should have added that the Derale unit is part number 16749 and the car is being wired with an EZ wiring harness...