AU Fans... Is One enough to cool the engine?

[ZZT231]

Hello All,

Is 1 AU Fan big enough to cool the engine as I'm thinking of hooking up the other for the Air Con or should I put a relay/diode thingy so when the A/C is switched on both fans come on, and when the thermo switch kicks in it will switch on but do nothing as it will not "override" the Air Con trigger?

Cheers.

[Mos]

Short answer: It should be Ok for radiator only.

Longer answer: Factory toyota setups in general run the two fans in series (low speed) when the A/C is switched on. The fans can then kick into parallel operation (high speed) when either (or both) of two things happens:
1) the A/C high pressure switch is activated (meaning the condenser is not getting enough airflow and the refrigerant pressure is rising).
2) the engine coolant temperature switch is activated (whether in the radiator or thermostat housing, depending on application).

The A/C condenser is probably more critical in having its full surface area subjected to airflow than the radiator. With only the MX83 factory condenser fan (front mounted, factory A/C high pressure operation only) the radiator was adequately cooled except on the hottest days, however the refrigerant pressure was rising outside normal ranges even on a moderately cool day (determined by monitoring of A/C refrigerant pressure gauges on a stationary vehicle at idle).

A factory cooling system in general has a very high heat shedding capacity. I don't know what the factor of "overrating" it is (anyone?) but even with a heavily (70%) blocked radiator it is able to provide adequate cooling in stock applications, in virtually everything but the extreme ambient temperatures. Duty cycle of full engine power will obviously affect this - the more power an engine generates the more heat the radiator will need to remove - if you're on full throttle say 60% of the time around a race track your cooling is a lot more critical than if you take part in the occasional traffic light grand prix (which none of us engage in of course) but otherwise take it easy.

Personal preference is to run two identical or similar fans in the toyota setup, because you're not wasting electrical power when you don't need to and you potentially increase the life of your fans.

Otherwise, hook up both fans in parallel and run them both if either the A/C is activated or the temperature of the coolant warrants their operation.

You can get away with running fans on all the time, as the engine thermostat will take care of temperature regulation, but generally this is considered a "temporary" solution until you fit a fan thermostat.

Mos.

[mrshin]

You can get away with running fans on all the time, as the engine thermostat will take care of temperature regulation, but generally this is considered a "temporary" solution until you fit a fan thermostat.

Mos.

Unless you're a Drift Kid, where is is absolutely necessary to remove your engine driven fan and replace it with a gutless Davies, Craig unit, which is wired to the ignition switch to run all the time (probably without a relay)

[mullett]

Well, as far as I understand it, if you don't stop or drive below 40km, you don't need a fan at all. So running it all the time would be pretty pointless. I guess it depends how much you need the cooling power. Try it and see!

RM.

[takai]

Speaking of thermofans, does anyone know what the tiny 8" one is for in the top passenger side of the MX83. I have never seen mine turn on, with or without aircon etc etc.

[Mos]

Speaking of thermofans, does anyone know what the tiny 8" one is for in the top passenger side of the MX83. I have never seen mine turn on, with or without aircon etc etc.

It runs in parallel with the one in front of the condenser - both of these only turn on when the A/C in on AND the refrigerant pressures are high enough to trip the pressure switch.
Mos.

[takai]

Ah, so the fact that half of my refrigerant has leaked out could be why it doesnt come on then. I assume ill want this as an extra input to the thermofan relays then

[Mos]

Ah, so the fact that half of my refrigerant has leaked out could be why it doesnt come on then. I assume ill want this as an extra input to the thermofan relays then

Yeah, amount of refrigerant has something to do with it

Well, depends on how you set up your fans. If you do the low speed series setup on A/C switch on, then definitely use the pressure switch to turn them on at full speed.
BUT if you run both thermos at full speed with A/C on then you won't have much available to you when the refrigernat pressure goes up (you are running two fans? - the el cheapo 14" supercheap auto fans fit perfectly)

Mos.

[takai]

Yeah, i was thinking of just getting two 14" supercrap thermofans. Wiring both up to the thermoswitch and one up to the AC relay.

That way i can keep the temps down, and also make sure that with AC on it will still not die, that and i can keep the fans on after the car has stopped after towing for a while.

[Mos]

You want to run both with the A/C... not just the one.. see second post in this thread.
Mos.