Fan speeds/ aux rad

[dan_b]

Hi gang
Today I got my aircon fixed, hooray! Sweat-free motoring has returned!
I am now worried about the cooling capacity in my 3B, boo...

I've been running without my aux rad for quite a while now and without aircon, it hasn't shown any signs of thermal stress whatsoever. Low speed fan comes on fairly regularly but always cycles off again after a short time. Nicely controlled thermostatic temperature, no worries.

Sitting in traffic today for about 20mins on not exactly the hottest summer's day with the aircon on, I heard for the first time since I've owned it the car switching the 2nd speed on the main cooling fan. And it stayed on for a long time.

Should I be worried? Do other people get the 2nd speed fan coming in whilst in traffic regularly? Should I be thinking of putting the Aux Rad back in?!

[S2central.net]

How fresh is your thermostat ?

[porkkis]

There is a high pressure switch for the fan after the condenser. If the weather is hot enough the condenser can't cope with it and then this switch indicates that condenser needs more air flow -> high speed on.

Completely normal.

[S2central.net]

Porkkis could be on the money here !

[dan_b]

I replaced the thermostat when my main rad went kaput about 3 months ago.
I guess I'm just paranoid now that having fixed the aircon to keep me cool, having removed the aux rad there's now not enough cooling headroom left to keep the engine cool!

Glad to hear it's completely normal, I was getting worried. Does this mean that people with aircon on the S2 in hot countries (eg. Spain) where you'd be wanting the aircon to be working when the weather is at its hottest that you get this even with the aux rad in?

[porkkis]

Even I have the fan running on high speed sometimes and our weather is not generally exactly hot...

It usually happens when the car is not moving -> heat soak in engine bay etc. You know.

[Pete_RS2]

Does this mean that cars without aircon only have two fan speeds, i.e. main speed & a lower speed for after-run ?

[porkkis]

With high speed I mean the "main speed".

Fan speeds and their usages vary a bit between model years etc so there is no easy explanation how all s2's use the fan.

3B 91 has 2 main speeds hi/lo and lo is normally used with aircon and without aircon when coolant exceeds temp x (can't remember), hi is used when aircon condenser needs it or coolant is very hot. Then there is a much lower speed for after run cooling.
One 92 car I looked at used the after run speed when aircon on..
ABY/ADU cars have different setups to 3B as they have a single speed fan motor (3B has internally 2 speeds). ABY/ADU use an external resistor pack. Don't know how the different speeds are used on these.

I'd think that the high speed is used by all A/C cars if necessary.

[audiman]

Thats right Porkkis. ABY/ADU has a seperate resistor pack. Speed 1 is after run, speed 2 is normal cooling and speed 3 is AC condenser high temp.

[dan_b]

High speed fan on the 3B is VERY loud! This is great though, puts my mind at ease a lot: I was starting to think of having to buy a new aux rad etc.

[sailaz]

Thats right Porkkis. ABY/ADU has a seperate resistor pack. Speed 1 is after run, speed 2 is normal cooling and speed 3 is AC condenser high temp.

I can confirm 100% that on ADU you won't find 'AC condenser high temp' switch/sensor. There is A/C high pressure switch for electric fan 8A0959482AB & safety switch for refrigerant compressor 8A0959482AA

when A/C high press. switch for electric fan is activated it's kicking in 2nd speed, NOT 3rd, I have confirmed that by bridge pin 2 to pin 3 on temp switch on the radiator and the 2nd stage fan was still running because of activated A/C high pressure switch for electric fan, then I bridge pin 3 to pin 1 and the 3rd stage was kicking in.

for reference from post #24

http://www.s2forum.com/forum/showthread.php?t=61194&page=2

[sailaz]

accidentally found this info: http://forums.quattroworld.com/s4s6/msgs/334580.phtml



A/C refrigerant high pressure switch -F23- Function

Switches coolant fan -V7- to 2nd speed operation.

Switch identification: green housing with bonded wire connections

Switch located on left side of condenser

Switch closes (2nd speed ON): 14.2-17.4 bar (206-252 psi)

Switch opens (2nd speed OFF): 11.7-15.0 bar (170-218 psi)

Removing and installing

Remove electrical connector and unscrew high pressure switch -F23-.

Refrigerant system remains closed (Schrader valve under switch)

Install new O-ring -A- (7.6 mm x 1.8 mm), lubricate with refrigerant (PAG) oil and ensure proper seating in groove.

Torque switch to 5 Nm (44 in lb).



A/C refrigerant high pressure switch -F118- Function

Switches A/C clutch OFF if system pressure is too high

Switch opens (compressor OFF): 28.2-31.0 bar (409-449 psi)

Switch closes (compressor ON): 10.3-17.3 bar (149-251 psi)

Switch identified by red housing, located on left side of condenser

Removing and installing

Remove electrical connector and remove high pressure switch.

Refrigerant system remains closed (valve under switch)

Install new O-ring -A- (9.3 mm x 1.8 mm).

Tightening torque: 5 Nm (44 in lb)