Cooling fan testing

[twoqu]

Just try and identify the relay that clicks when you bridge the middle terminal and substitute it wih an identical one to eliminate it!
Seem to recall that both the 1st and 2nd speed relays are in the fuse box under the bonnet. Think they are the 214 grey relays. If substitution works then you will have to decide whats better to do without temporarily .

[Error404]

sorry typo! Corrected!

Yeah bridging the afterrun pump switch should activate the pump and the low rad fan speed continuously until you separate them

[UrS4boy]

The new 2 pin MFTS will read two notches higher. This is not an accurate temperature measurement any more.

2 Pin MFTS?

Recently we talked about the old 4 pin being superceded (an long number of years ago) to 3 pin and now you are talking 2 pin??

BTW, I had to replace a failed 4 pin with a 3 pin around 2002 or 3. The coolant temp readings have been accurate since (checked against Ch.51 in the auto climate control head unit).

[UrS4boy]

Seem to recall that both the 1st and 2nd speed relays are in the fuse box under the bonnet. Think they are the 214 grey relays.

Yup, as shown in my after-run pump and fan post:



The one is clearly shown, front right. The other 214 (the Delay fan relay), is hiding behind the black 229 relay/module, middle rear.

[Monkeymagic]

I only way I can get a fan On is bridging terminals 1 and 3. I'll tmake a look at the relay in the fuse Box.
I'll assume the 324 module is functioning as the after run pump works but without the fan which looks to connected through the relay.
The lack of after run fan and seemingly 2nd stage fan the common part is the relay? I think.?

[Monkeymagic]

Ah yes just read the updates. As for the Mfts as the old one was goosed I'll assume the New one is accurate. Thank you all ste

[Fat Audi 80]

2 Pin MFTS?

Recently we talked about the old 4 pin being superceded (an long number of years ago) to 3 pin and now you are talking 2 pin??

BTW, I had to replace a failed 4 pin with a 3 pin around 2002 or 3. The coolant temp readings have been accurate since (checked against Ch.51 in the auto climate control head unit).

Sorry 3 pin, should not post from my 41 year old memory!

Yes there are documented instances of poorly calibrated MFTS' s, mine being one of them....

(Mine was replaced last year)

Cheers

Steve

[UrS4boy]

I'll assume the 324 module is functioning as the after run pump works but without the fan which looks to connected through the relay.
The lack of after run fan and seemingly 2nd stage fan the common part is the relay? I think.?

In reference to the diagram below (written for a C4 UrS4/S6 but the logic is the same for a B3/S4 S2 and RS2), try not to let your eyes glaze over, read through more than once, if necessary (you are the one who wants the answers) :

In general, the after-run pump and stage 1 of the rad fan only come on if the temperatures *AFTER* engine shut down exceed 110 C. If this happens the F98 Thermal Switch triggers the J155 After-run pump and fan control "324" module to fire up the pump and stage 1 of the rad fan until the temp drops to 97 C or 10 minutes have gone by, whichever comes first.

But that is skipping ahead. Backing up, the power for the after-run pump comes from the No.30 constant power bus in a red wire to the S61 fuse (a branch of that red wire also goes to the S26/102 ECU fuse that feeds pin T55/18 on the ECU (this is for the AAN, ABY/ADU different numbers but the same idea). After the S61, the wire is white/black and heads to the two pin After-run pump connector.

At the after-run pump connector, a second white/black wire branches off to the F98 thermal switch. When this switch closes at 110 C or above, the current flows to the J155 ("324") after-run pump and fan control module in a red/green wire going to pin 2/30 on the module. The module itself is energized by switch power from the J17 fuel pump relay via the S73 thermal fuse that also feeds the O2 sensor heater. From the S73, a yellow wire feeds the J155 (324) module at Pin 4/87F. This is a switched power signal so it must help the 324 determine whether the engine (and ignition) is off. If the engine is on, then even if the temps are up, then I don't think the after run-pump and/or fan will run because the 324 says, "Nope, not happening, let the water pump do its thing". (so to speak).

With the signal from the closed F98 thermal switch, the J155 (324) control module opens up a ground for the after-run pump at the module's Pin 8/87. Power flows through the V51 after-run pump in the white/black wire and out via the brown/black wire connected to the control module's Pin 8/87 (which then flows out to ground (earth) at the module's Pin 6/31).

In the meantime, the J69 (214) Stage 1 rad fan relay has been sitting with power (but no ground (earth)) from the S19 (AAN number) fuse via a red/white wire to J69 pin 2/30 and a red wire to J69 pin 5/85. When the J155 (324) gets the closed signal from the F98 thermal switch, a ground for the J69 (214) relay is opened at J69 pin 4/86. This pulls the relay on and power then flows through the S19 fuse, through the J69 (214) and out to the V7 rad fan (Stage 1) as a red/white wire from J69 Pin 8/87.

This continues on until the temp drops to 97 C and the F98 thermal switch opens again or the internal timer in the J155 (324) control module times out at 10 minutes. Presumably if the temp was not less than 110 C then, the process would repeat itself.

[Monkeymagic]

Urs4 boy. Trust me I've tried!
This morning I have bridged the thermostat switch for the after run pump and I only get the pump kicking in. No fan.
I definitely only get the fan On when bridging wires 2 and 3 for rad fan.
I've swapped the 214 relays of which I have 3 and nothing changed.
what's next the 324 control module? Sorry gguys its not my strong point

[Error404]

Can you hear the relays clicking when you bridge the rad thermo switch pins? I doubt the 324 module is faulty if stage 2 doesn't work either.
Check the fan connector, on the 3b there are 3 pins, two 12v supplies from the relays and an earth. Maybe the pin for the 2nd stage relay is damaged, loose, crusty etc
Check continuity between the thermo switch and relay terminals too

[Monkeymagic]

I can hear some clicking but I'm working on my own. I reckon I'm going to hand it to an auto spark. I get out my depth with these things.

[Monkeymagic]

I've checked the plug to the fan motor they look like New. I'll get some hired help later and see which relay click when bridging the middle terminal

[Mikes2]

There's also a resistor pack located down in the wheel arch close to the windscreen water bottle. Seen corroded terminals on this sometimes causing problems

I take it you are testing this with the ignition on for speeds 2 and 3

[Error404]

There is a resistor pack on the 3B?

[twoqu]

Of course its possible that the fans first stage has failed. That would leave you without the first and second stage fan speeds as the difference is speed is down to the resistor on the after run giving you less voltage.
You could check this by measuring for voltage at the fan terminal when bridging either the after run switch (first stage) or the rad switch. If you have voltage at the fan and its not working then we have eliminated all the other components. Electrics seems complicated but basically its looking for signal/voltage etc. Certaintly within the capability of most mechanically minded.