Install Manual Cooling Fan Switch

[fatsodoctor]

Lots of posts about baffling and aggravating overheating issues. Probably a variety of causes and a variety of solutions.

I'd like to install a manual cooling fan switch on top of the existing fuse/relay system, so that the engine temperature and the ECU and whatever else is involved still operates the fan as designed, but I will be able to turn the fan on and off manually when I am stuck in traffic during another Memphis heat advisory.

I understand one method is to splice into the green wire of the temperature switch, send the splice to a switch in the cab, and the switch to ground.

But I'm not wild about splicing into wires.

What's the simplest, most unobtrusive way to manually operate the cooling fan?

(Can you 'splice' into the cooling fan relay, itself, with a wire inserted into one of the relay's connectors? That would avoid altering any of the engine's wiring--but which of the relay's pins?)

 

[guynlidia2006]

Easy way is to splice into the ground wire on the fan switch, when you lick the switch it just completes the ground and turns the fan on and you done have to worry about fuses or relays...

 

[fatsodoctor]

Right. I understand that I can splice into the wire on the fan switch.

What I'm wondering is whether it's safe to insert a new ground wire into one of the cooling fan relay connections, and, if so, which of the relay's connectors do I want? (#86, maybe?)

 

[fatsodoctor]

The answer to my question turns out to be 'yes'.

You can slip a wire into pin #85 of the cooling fan relay. You run this wire to a switch. Run the switch to ground. Then you have a switch that will turn on the cooling fan without changing any of the car's hardware. The relay still tells the fan to go on and off, according to the signals it receives from the ECU, the thermoswitch, and from wherever else. And you can turn the fan on and off yourself, besides.

Don't, whatever you do, touch the wire to the receptacle for pin #30. That's a very angry receptacle. Have plenty of 7.5 and 20 amp fuses on hand if you decide to go hunting for the right pin (there's a diagram on the relay itself that identifies the pins).

The switch doesn't change the fact that there's something wrong with my car. I understand that I haven't solved any problems. But having replaced switches and radiators and thermostats with no luck, I have to be able to keep driving this car while I continue diagnosing it. The switch helps me keep it going while I keep looking for the problem.

Speaking of which, here's another symptom:

I'm driving in the afternoon. The engine is well warmed up, but not overheating. I come to a stop at a stoplight, and, out of curiosity, I turn off the air conditioner, turn the cab temperature to as-hot-as-possible, and turn the blower on high.

No hot air. Cool air (not refrigerated by the AC, but definitely not hot).

The light goes green. As soon as I start moving, hot air comes through the blowers.

So, at the next light I do the same thing, only this time, I set the parking break and rev the engine. When the engine is idling, no hot air. When I give the engine some gas (whether or not the car is moving), hot air.

What little I know about this car tells me that the hot coolant is not circulating through the heater core, hence, no hot air.

But what's the mechanical problem that circulates coolant through the heater core only when the engine is revving?