Aircon Help

[Colin P]

Hi all, my aircon is making strange whoop noises which i am led to believe is quite common. Is there an easy way to check the system is working properly or is a case of simply re-gassing.
Thanks
Colin.

[bl52krz]

Take it to an aircon specialist. Prob wants a regas as you said, and no harm done if it has a vacuum out and a regassed. Don't use one of the regas efforts from Halfords because you will not get a proper result. Our cars are getting on a bit now, so a good vacuum and check for leaks before the regas can only be a good thing.

[Colin P]

when i look through the front grille i can see the big fan. When the aircon is turned on the fan does not work could this be the reason?

[SD1too]

Yes Colin. You'll need the ignition on, when the radiator fan should run continuously at slow speed after pressing the windscreen demist button.

Can you see a silver resistor through the grille? If so, that will be the culprit, probably. ;)

Simon

[Colin P]

Yes Colin. You'll need the ignition on, when the radiator fan should run continuously at slow speed after pressing the windscreen demist button.

Can you see a silver resistor through the grille? If so, that will be the culprit, probably. ;)

Simon

I cant see the resistor at 2.00 on the fan where it should be.

[SD1too]

You could have a 3 speed fan then. Either way, you'll need to remove the front bumper to make repairs, and all will be revealed then!

Simon

[Colin P]

You could have a 3 speed fan then. Either way, you'll need to remove the front bumper to make repairs, and all will be revealed then!

Simon

If i have a 3 speed fan do i still need to change the resistor or is it a new fan.

[SD1too]

3 speed fans don't have a resistor. The slow speed stops because its earth brush wears down to nothing. If you catch it in time, a new one can be fitted very inexpensively if you're a keen DIY type!

Simon

[Darcydog]

I will bow to others greater experience here re the cure - but I have exactly the same issue.

3 speed fan - not working on low speed when it should.

My air con does work but i make sure I am doing over 30mph when I use it.

Re the cure - I am going to try replacing the motors brushes first

I cut and paste this a while back re checking the fan - not done it yet but I must get round to it


The fan speeds for the diesel are controlled by a PWM waveform from the main ECU. This signal is sent on a single wire and is processed by a PCB in the control box. The relays are then energised accordingly. The only component in the control box which you can realistically check are the relays.

The most likely cause of failure though is one or two of the motor brushes. You can run the motor directly from a battery as Stocktake has advised:

1. Connect the black cable to battery negative for the duration of the test.

2. Connecting the slate (grey) cable to battery positive should cause the fan to run at low speed (my guess is that it won't).

3. Leaving the slate cable connected as above, add the red cable to the positive battery terminal. Medium speed should be the result (again, I suspect that you'll get nothing).

4. Leaving all the above cables connected as described, connect the purple cable to battery negative. The fan motor should then turn at high speed (and it will!).

But as advised earlier, you'd be better off removing the motor end cap as I'm sure that you'll find a worn brush or two or, if you're unlucky, a scene of more serious destruction.


I have the brushes - you can get them here:-

http://www.engineeringcarbonproducts.com/rover75-carbon-brushes.php

And there is a stunningly good "How To" here:-

http://www.the75andztclub.co.uk/forum/showpost.php?p=387615&postcount=10

[suzublu]

Moved to Technical help :}

[TomRS]

My fans dont work on either of my diesels... worth just replacing with a Revo fan or similar?

[Colin P]

My fans dont work on either of my diesels... worth just replacing with a Revo fan or similar?

Is that an easy job to do?

[SD1too]

It's about the same as renewing a motor brush or two Colin. Here are the differences:

New brushes

Remove motor end cap by bending back securing tabs. Lift off.
Place socket over the commutator and remove worn brushes. Cut braiding.
Solder in new brushes.
Refit end cap.


Replacement system

For Revotec, I understand that the shrouding needs to be modified.
Modify wiring to change from 3 speed operation to 2 speed.
For second-hand MGR 2 speed, fit gold resistor in place of silver.


That's not a comprehensive list, just to give you an idea. A replacement Revotec is considerably more expensive than fitting new brushes on your motor which is probably perfectly OK.

Simon

[Colin P]

It's about the same as renewing a motor brush or two Colin. Here are the differences:

New brushes

Remove motor end cap by bending back securing tabs. Lift off.
Place socket over the commutator and remove worn brushes. Cut braiding.
Solder in new brushes.
Refit end cap.


Replacement system

For Revotec, I understand that the shrouding needs to be modified.
Modify wiring to change from 3 speed operation to 2 speed.
For second-hand MGR 2 speed, fit gold resistor in place of silver.


That's not a comprehensive list, just to give you an idea. A replacement Revotec is considerably more expensive than fitting new brushes on your motor which is probably perfectly OK.

Simon

Thanks for your help appreciate it. I havnt used a soldering iron before but i,ll try anything once lol.

[kboy]

is there a guide for modify the wiring from three to two speed pls.

[Sector-9]

For soldering the brushes, you'll need a high power iron (maybe a gas one would work better) - I found my 100W gun was smoking before the solder had melted, and a standard 35W wand on it's own just couldn't get the joints hot enough. Thankfully using both at the same time got the job done, though this would be best with an assistant unless you're like that Hindu god or an octopus!

[SD1too]

is there a guide for modify the wiring from three to two speed pls.
Here you go. (http://www.the75andztclub.co.uk/forum/showpost.php?p=1936633&postcount=1) This is for the MG Rover system. For Revotec, supplier Jules provides installation instructions.

Simon