aircon fan

[genpk]

Slowly getting though all the jobs to get my doer upper 75 back to top condition.Exterior of the car is almost show room (owned by a retied barrister) Finished re trimming the A pillars,put a new metal thermostat in,odd blown fuse, fix the VIS motor,just changed the engine and transmission oils,sorted the vibration out (exhaust vibrating against cross brackets),wrong exhaust rubber hangers)
Thought I had just about covered it all then I go to switch the aircon on, switches on but nothing but warm air blowing!!!
It has the old 3 speed fan,the fan is kicking in and out on the engine as per normal but does nothing when you hit the aircon.
Not sure which way to go, either a new original one (very expensive) fit a kenlowe system, or use a secondhand 3 speed I have out of a car with similar mileage (120,000km)

[john2443]

I don't think it's the fan causing the problem, more likely to be no gas in the aircon.

Have you tried the tests here? http://www.the75andztclub.co.uk/forum/showthread.php?t=35567

[SD1too]

I don't think it's the fan causing the problem, more likely to be no gas in the aircon.
That's only true of the diesel ECM John. The fan runs independently of refrigerant charge on the petrol engined cars.
... the fan is kicking in and out on the engine as per normal but does nothing when you hit the aircon.
On the face of it, that sounds rather odd. Just to be sure, test it using the windscreen demist button rather than 'auto', and ensure that the engine is running.

Also, activate the instrument pack diagnostics to display coolant temperature and go for a drive with air con. off (Econ mode selected). Let us know if the radiator fan starts running at 100°C.

Simon

[genpk]

I think the previous owner said he had it tested and was told that the system had gas in it but they couldnt figure out why it wasnt working.He thought it might be the compressor
Having said that I will get it checked.
Would the lack of gas stop just the aircon part of the fan activating ?
Further, when I switch the aircon on ,apart from hot /ambient air ,the weird thing is when I change the temp settings up or down seems to alter the blower fan speed. Not seen that on any of my other 75s.
Dont suppose the car using waterless coolant would be affecting anything as the radiator fan still appears to be working when required.

[SD1too]

Peter; please carry out the tests described in my last post and let me know the result. That is the way to find the problem with your fan.

Simon

[genpk]

Really interesting thread.Ill give the short circuit trinary switch a go tomorow and see what the deal is. Appears that the engine fan can still work but the other speeds may be worn out. I would have thought the main high speed used to cool the engine would have worn out quicker due to more use than the aircon related speeds though.
My last one that went faulty was the main hi speed fan brushes so I had no cooling to the radiator in stop start traffic thus it overheated.

[SD1too]

Ill give the short circuit trinary switch a go tomorow and see what the deal is.
You need to establish whether or not the slow fan speed is working. The trinary switch test will not do that.
Appears that the engine fan can still work but the other speeds may be worn out. I would have thought the main high speed used to cool the engine would have worn out quicker due to more use than the aircon related speeds though. My last one that went faulty was the main hi speed fan brushes so I had no cooling to the radiator in stop start traffic thus it overheated.
Peter, you are very confused. Please carry out the windscreen demist test as I recommended and tell me the temperature at which your fan starts running as described in my earlier post.

Simon

[genpk]

Hi Simon,im not really confused just trying to sort out the aircon.
Dont worry, life is really good !!!
I did the demister test and sure enough no fan activated
It is the older 3 speed fan.
So today, took the fan out,pulled it to bits,sure enough 3 half worn brushes and one totally worn down.
Explains why I still had the cooling fan but no aircon.
Just so happens I had a spare set of brushes I bought ages ago to do another motor rebuild.
Fan works great now and when I activate the aircon it comes on.
Only issue is the aircon is still blowing warm air and when I hit the on button both the aircon and recycle lights come onI,also notice that the outside temp sender is reading the temp as 20 to 25 c which today it is about 35 c ??
I have heard when you diconnect the sensor it can take time to recallibrate .
Mu question is,would the temp sensor affect the running of the aircon.

as a mater of interest ,a couple of great tips I picked up from other posters when removing the fan, you can replace the fan without taking the whole fan surround off or cutting anything around the aircon pipes, just pull the passenger side of the nylon surround forward and thers enough room to get to the 3 fan mounting screws and then you can feed the control box and wiring out the hole where the fan motor was.
The other bit of help is you dont need to remove your bonnet latches from the slam panel,just disconnect the two bonnet cables at the small connector box near the power steering resvouir .
Does the system do anthing to indicate low gas?

[SD1too]

Does the system do anthing to indicate low gas?
No. You'll need to book an air con. practitioner to attach a gauge set and examine the operating pressures.

Simon

[genpk]

Got the aircon regassed and all is good.Thanks for everyones help to understand how these aircon system works.
Aircon guy reckons the denso compressors hardly ever pack up as there built like tanks and top quality units.
The other interesting thing he mentioned was you should run the aircon at least once a month to keep the oil moving in the system to keep the o ring seals good and that even if the aircon does dry out,it will loose the gas but once re gassd the o rings will expand again and seal once again .
Aircon is icy cold !!! thank god, its been in the high 30s over here.
Moral of the story - on the old 3 speed fan, you can still have a working cooling fan for the radiator but a failed aircon fan and that will stop the unit from working.
As SD1too mentioned,the demist button will tell you wheather its working or not.
Further with low pressure in the system it will not trigger the switch to fire up the compessor.

[SD1too]

... sure enough 3 half worn brushes and one totally worn down. Explains why I still had the cooling fan but no aircon.


Moral of the story - on the old 3 speed fan, you can still have a working cooling fan for the radiator but a failed aircon fan ...
Yes Peter, your completely worn down brush was most likely the earth for low and medium speeds causing their complete loss. The remaining three brushes would have provided engine cooling but only at the alarmingly high temperature of 112° and with the motor rotating at medium speed rather than fast. Since this temperature is perilously close to official overheating with red lights flashing, it should not be described as "a working cooling fan for the radiator". It's a situation which requires an urgent repair to prevent a breakdown and possibly engine damage.

Thanks for keeping us informed Peter, and well done for repairing what is, after all, a perfectly serviceable motor. :D

Simon

[genpk]

Thanks Simon,thanks for your informative help on this,this motor had a perfectly clean armature ?,so was a great candidate to re brush.
The last one I pulled to bits had a great gouge through the middle of the copper from one of the brushes so wasnt worth re brushing.
As for a servicable motor,your dead right, Seimens certainly know how to build a good electirc motor.the bearings were still smooth.
After I had done the repair,a friend of mine who does electric motor servicing gave me a good bit of info if ever again doing it,clean down the copper armature and get a tiny screw driver and clean out all the carbon in between each of the copper plates on the conductors.

Onto the next job,getting a vibration under the floor pan when putting it into drive,seems to reduce alot when the engine gets warmed up.
The exhaust pipe was touching the 2 small cross bars under the car,put new rubber hangers on,its reduced it but think either rear engine mount or the engine mount under the battery box may be stuffed.
Onward and upward!!!

Finally got under the car today and found the vibration issue when in drive,the infamous lower engine mount was split in two.
Waiting for powerflex one to arrive ,meantime packed the old one with some rubber blocks had laying around and its running beautifully !!!!