Help wiring electric fan to turn on with air conditioning

[HelpIAmAParrot]

I'm following the Volvo electric fan swap on my 92 Ranger. I got it all installed and went to test it last night (fans never did come on, thinking I need to recheck my grounds) and while the truck was warming up in my driveway it triggered the relief valve in the AC compressor (scaring the bejeezus out of me). I hadn't realized my AC was running, and I realized it was because with no airflow the refrigerant wasn't cooling off enough in the condenser and therefore couldn't go back to it's liquid state, over pressuring the system and blowing out the relief valve. It happened at a relatively low temperature too, I suspect lower than the 195⁰F that would trigger the low speed fan.

So I got to thinking, it would probably be wise to wire in a way to override the temp switch that I plumbed into the upper radiator hose so that any time the AC is on, the fan will come on low speed. When moving obviously it wouldn't be much of a problem anyway, but if I were for example sitting in a parking lot with the AC on in the summer, the same thing would happen.

I'm following the below wiring diagram- would it be possible to do the wiring I described with the relay built as it is? I'm still a beginner when it comes to engineering my own electrical diagrams, so thought I would check with the experts.

 

[RonD]

This is a more detailed diagram of Volvo Relay assembly: https://www.therangerstation.com/tech_library/images/volvo_diagram.JPG

So its basically 2 relays in a "box", one for low speed one for high speed
Relays get 12v with key on
Then each relay is Grounded to activate it by a Temp Switch on heater hose or upper rad hose
Make sure Temp Switch is always in contact with Coolant or it can't work

And manually Ground each temp switch wire to see if fan comes on, engine on or off doesn't matter, but 12v must be on


Easiest way to add AC on/fan on is with another relay
AC Compressor clutch gets 12v to turn AC on
Splice into that wire
Low speed fan is activated by Ground wire at Temp Switch, splice into that wire

Relays use 85 and 86 to activate, no polarity, as long as one is 12v and the other a ground relay closes
Standard automotive Relay Diagram here: http://www.gtsparkplugs.com/images/mini-automotive-relay-wiring-840x.jpg

Connect Low speed ground splice wire to 87
Connect chassis Ground to 85 and 30
Connect 12v AC splice wire to 86

When AC is activated the 12v closes the relay
87 and 30 are then connected, grounds the Volvo Relay
Low speed fan turns on same as if Temp Switch Grounded it

If low or high speed was already on it wouldn't change anything by ground that Temp Switch wire


I personally don't think you should have a on/off switch for the fan, just key on power
If you want the on/off switch then make sure you wire in a bright RED Light to notify you when fan is switched off

 

[HelpIAmAParrot]

Update: I drew this on a napkin at a certain Owl-themed wings restaurant. Would this work without burning my truck down? My thinking is I want the low circuit on with AC, but if temps climb high enough I want the low circuit to kick off and normal Hi circuit operation to take over.

 

[HelpIAmAParrot]

Thanks for the reply! The fan switch is supposedly for if you go through a high water crossing, which I don't foresee doing regularly but might be a nice feature to have nonetheless. I added another post without seeing your reply but it seems like we may be close to on the same page, though I like your solution of using a single additional relay with the temp switch ground wires better. All the wiring knowhow I have comes from experience/my own research so I'm sure there are gaps in my knowledge and I wanted to make sure I was at least somewhat on track.

Edit: if I'm understanding you right, it would look like this?

 

[RonD]

Yes, that would be correct

In general high water crossings are not a surprise, so you could just unplug fan connector or pull fuse when you need to
Forgetting to turn the fan on would be the more apparent danger


If you decide to use a switch in the cab then use the Ground on that relay for it's on/off control, keeps the 12v wiring shorter and all in the engine bay
1 small wire from ground pole(85 or 86) on relay into the cab to the switch, ground the switch locally(cab ground)

You can get key on 12v from IAC valve, EGR solenoid, coil pack even fuel injector wire, and these do not have 12v in ACC
Relay control circuit is 0.5amp(500mA) so can be added to any fused circuit without an issue