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[General] How To Diagnose HVAC Fan Problems VT - VZ

Nut Kracker

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THIS "HOW TO" IS ONLY FOR THE MANUAL HVAC SYSTEM AND NOT FOR THE AUTOMATIC CLIMATE CONTROL.

I've been looking around this Forum and I have found that alot of responses as to why the HVAC
(Heating, Ventilation and Air Conditioning) fan is not working, is that the resistors have packed it in.
This is not entirely true.
The fan switch is divided into two parts. Firstly, the lower speeds, 1,2 and 3 run through the resistors to the fan. The 4th speed (High) by passes the resistors and runs directly to the fan via the blower relay. There is NO resistance on the 4th speed.
That means you can pull the fuse or remove the blower relay and the 1st, 2nd and 3rd speeds will still work.
If the fans don't work at all, it is very unlikely (however possible) that both the blower relay and the resistors have failed simultaneously.
It could be...
1) The Blower Inhibit Relay. This relay turns on when the car is started, regardless if the fan is switched on or not.
2) The Fan Switch.
3) The Fan Motor it's self.
4) The BCM.
5) Wiring faults (Shorts etc.).
6) The Blower Fusible Link/s
7) The Main Fusible Link. (That would mean NOTHING on the car would work). Hey, Don't laugh!
8) Fuses.
If only the first 3 speeds aren't working and the 4th speed IS, then yes, it could be is the resistors, the BCM, the fan switch is faulty or faulty wiring.

If only the 4th (High) speed isn't working, then the Blower relay may be faulty, The number 13 Blower Relay Fuse (7.5 amp) VT-VX or The number F22 Demister Fuse (20amp) VZ may be blown (The VZ F22 fuse protects both the Blower and Demistor Relay circuits),
again the fan switch and again faulty wiring.

The HVAC is not really a complicated circuit compared to other circuits on these cars. It's physically finding the fault as you all know is the problem. It's not as easy on more modern cars as it is on older ones. It's just a matter of "process of elimination". Start with the easiest solutions first and then work your way towards the harder ones.

Anyway, I hope this helps anyone with these problems and if there is anyone who can add to this, please do, as it's late and my brain is a bit fuzzy.
 
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jughead1

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Hi,

In my VX Series II when we use the 4th setting on the fan, sometimes cuts out, then will come on again after a little while. Looks like the fan cuts out under heavy load. Could thsi be the relay or is it a design feature to give more poertr to the engine (turn off AC) under heavy engine load?

Cheers,

JG
 

Nut Kracker

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By heavy load, you mean engine load (revs)?
I would say it's possibly the blower relay breaking down. Or it also could be the blower inhibiter relay.
Also check the voltage at higher rpm (about 2500rpm) just to make sure your alternator is not putting out too much voltage.
They are both under the steering wheel in the fuse compartment.
The fan wont turn off under load.
The A/C compressor is designed to turn off a high revs such as wide open throttle (WOT) so as not to over rev the compressor, but the fan will stay on.
 

jughead1

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Thanks for that.

My alterantor could be the problem. Recently the battery light has been coming on after the car has been in city traffic, but rarely comes on after a 45 km jaunt doen the freeway.
I changed the regulator and battery, and the problem went away for a few weeks, but now is back.

At idle, the alternator puts out about 14.6 v (at the battery). Someone mentioned that it should be 14.3 v. Would that make a difference?

BTW, th efan issue has been happening since we bought the car 6 years ago, but the battery light issue only started a couple of months ago.

Cheers.
 

Nut Kracker

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Yeah 14.2 / 14.3. that should be the limit. That extra voltage could make a difference. Remember that the relays are rated at 12 volts, so any extra could do some damage.
 

mpower

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helpful thread, sometimes my high speed cuts out in my VXII Clubport. I think it might be the switch as you flick it to 3 and back and it comes back on going off what I's reading here though it might be the relay - food for thought.
 

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helpful thread, sometimes my high speed cuts out in my VXII Clubport. I think it might be the switch as you flick it to 3 and back and it comes back on going off what I's reading here though it might be the relay - food for thought.
Even though your relay is clicking, the other contacts in it may not be working.
Try taking out the relay and powering up pins 85 and 86 to 12 volts, this will "click the relay". Then put a multi meter across pins 30 and 87, there should be continuity.
 

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my vz commodore fan speed works, but at half the speed or less, affects the aircon in keeping up, also high fan speed has huge noise coming from motor. What could solution be , have had suggestions to clean out debris from fan motor ?
 

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my vz commodore fan speed works, but at half the speed or less, affects the aircon in keeping up, also high fan speed has huge noise coming from motor. What could solution be , have had suggestions to clean out debris from fan motor ?
The suggestions to clean or replace the fan motor is what I would do.
The fact that it is not only running slow on the low speeds, as well as being
very noisy on the high speed, suggests the motor is clogged or is on the way out.
Not only does the fan blow out hot/cold air, it also has to draw that air in to blow it out. In doing so, it picks up all sorts of dust and rubbish which gets caught up in the guts of the motor.
I remember I had a noisy fan in an old EF Falcon. Turned out a chocolate bar rapper got sucked up into it.
You have to remember that the fan motor does have a hard life and in the cars on this forum, they are up to and over 30 years old.

Edit:
I personally wouldn't use the fan if it is running that slow and noisy.
It will put a heavier than normal load on the motor, which could shorten it's life dramatically. Especially if it decides to start to overload the circuit.
I know the fuse will blow, but the fan is connected to a 60 amp fusible link and alot of damage can be done before that blows.
 
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XOFICR

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1st speed is working but number 2 3 4 isn't.

The suggestions to clean or replace the fan motor is what I would do.
The fact that it is not only running slow on the low speeds, as well as being
very noisy on the high speed, suggests the motor is clogged or is on the way out.
Not only does the fan blow out hot/cold air, it also has to draw that air in to blow it out. In doing so, it picks up all sorts of dust and rubbish which gets caught up in the guts of the motor.
I remember I had a noisy fan in an old EF Falcon. Turned out a chocolate bar rapper got sucked up into it.
You have to remember that the fan motor does have a hard life and in the cars on this forum, they are up to and over 30 years old.

Edit:
I personally wouldn't use the fan if it is running that slow and noisy.
It will put a heavier than normal load on the motor, which could shorten it's life dramatically. Especially if it decides to start to overload the circuit.
I know the fuse will blow, but the fan is connected to a 60 amp fusible link and alot of damage can be done before that blows.
What do i look for if the 1st speed is working but 2 3 & 4 isn't, this started after I had a led conversion done to the controls.
 
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