Heater/blower not working

[TimboTheKiwi]

Hey guys n gals...I have a 96 UCS69 4JG2 Auto.

A weird thing keeps happening in that the blower/heater will not be working when I get in the vehicle from time to time. It never actually turns off - it is either working when I get in the vehicle or it is not, then the next day or 2 it will spring back into life when I get in it. Over the past couple of months it has happened about once a week, but now is occurring more frequently. Reading around a bit I see there is a resistor in there somewhere which ppl say could be the issue. Anyone know where this is located? Note this is just the blower/heater - not the AC which is no longer fitted. The lights on the dials/buttons will illuminate and I can hear the motors for the different modes working as normal (ie changing from 'window defrost' then changing it to say "Legs")...but it just won't blow anything!

Wouldn't normally bother me but it is getting fresh down here in christchurch.

Anyone else experienced this kind of thing and perhaps found the problem? I know its a kind of 'how longs a piece of string' question but thought I would start here before ripping the dash to bits/going to a auto sparky.

Thanks in advance, appreciate it!

[stardog]

The resistor is behind the glove box in the 96 wizard they are different to the MU ones.
If I remember right you undo the screws on the glove box hinges and the glove box should lift out.

[TimboTheKiwi]

Cheers stardog - Im still not sure if this is the problem as the dial stays true to where you set it (when it does function) but will have a tinkle with what you have described

[DonaldNZ]

Also In chch. Mine is a 97 ucs69 wizard.

My cabin climate control and heater fan will only light up and work if the key on & engine running.

if your heater fan is running, key off, without the dials lit up.

I'd first be checking at the speed controller.
in olden days it was a fan speed resistor stack located in the airflow so its cooled as its very very inefficient and as a result gives off a lot of heat. Each additional resistor added to the stack added by the heater fan 3 or 4 speed switch to make it go slower. Fast was no resistor. Usually has 3-4 wires of similar thickness and a ceramic blob or nichrome wire same stuff as toaster and cig lighter. Usually located in the heater box handy to the fan motor as stardog said behind the glove box usually held in with two phillips screws. If you touch it when removed & select low or med speed it burns your fingers.

Resistor failure usually due to trash in the fan restricting its rotation increasing current consumption and not blowing the larger than specified heater fan fuse po [previous owner] fitted. Pens, broken glass from broken windscreen, spare parts, coins, leaves.
Blockages in the airflow downstream actually reduce the power consumed. {try it with you centrifugal bilge pump] Never failure to always on caused by this older resistor stack.

My 97 has Off / Auto / Lo to Hi heater fan knob with 11 speed selections.
If yours is like this then most likely an electronic version of the above resistor but alas a heater computer is involved to control the heater auto functions and tell the speed controller how much to turn on.
Located in the same place as the speed resistor because they are inefficient [=cheaper to make] The electronic version [of the above resistor] still controls the fan speed but usually by controlling duty cycle or portion of on to off time say 5000 times a second.
Difficult to test without an oscilloscope or voltmeter and factory service manual specification. We can guess though. If yours is the electronic version with the auto position on the fan speed knob,
I've replaced only two of these electronic speed controllers in 30 years, one in a Citroen and other a Nissan.
I'd start with looking at for thermal damage at the plug [causing the intermittent no go] this thermal overheat can cause a short circuit in the internal transistor latching the heater on.
Then pull the plug out of the speed controller behind the glove box and join the two thicker wires together {a split pin will do but a copper wire wont get as hot and melt the terminals], should make the heater fan come on fastest. Drive it like that for 3 or 4 different driving days in a row and see if it turns off while driving then report back.

This as you may have two different symptoms, staying on and not going.
So joining wires together is testing the power circuit and the heater fan motor. you may have to disconnect it each time you get in and out.

Do you have access to a dc volt meter [any cheap $20 digital multi meter will do it] ?
Do you have a 12v test light ? [12v 5w bulb with a wire attached ?

[turnturn]

viewtopic.php?f=24&t=332&hilit=+heater

[TimboTheKiwi]

Cheers for info Don.

Ill have a look at that resistor you speak of...and yes I do have a wee cheap multimeter

[DonaldNZ]

We have yet to establish if the speed controller or the heater computer is at fault telling speed controller bad info, fortunately I can measure mine to compare.

Check if you have a off / auto / 11 speed positions first

[TimboTheKiwi]

Yes it is the one you describe with off / auto / 11 speed positions

[DonaldNZ]

ok,
Unfortunately after looking at Isuzu fsm [factory service manual] for 96 to 02 last night, they all talk about resistors with a 4 speed switch so quite useless.

And for interest, the ceramic heater is quite different mode wise, mine comes on with fan at any speed and heater set temperature at anything [although I havnt tried it below 20 degrees C] Therefor I do suggest you charge your battery overnight with a quality charger once a month especially in winter unless you are driving to Dunedin or similar once a fortnight.
A fully charged battery has a lower freezing temperature and will last significantly longer as Flooded Lead Acid [FLA] batteries like to be at 100% state of charge.

I think the ucs69 heater is the best heater Ive ever owned. I do like the ceramic, it is better than noticeable, I use it on low fan speed. a seat warmer would be nice too.

meanwhile back to the heater fan
find speed controller in blower box same as resistor position as per above info.
check wires , probably two thick & two thin

Let me know colours and join two thick wires together and report

test it like this for several days driving to confirm a good fan run on high without hesitation.

An easier way might be wiring a cheap toggle on/off switch between the two thick wires to avoid shoving a wire in and out each drive cycle to avoid spreading the terminals and loosing terminal tension.

take multi meter and select DC volts 20 v setting or similar.test it by putting across battery terminals and it should read around 12-13v. test it half a doz times on battery and observe same result repeated.

With speed controller plug removed from speed controller I'd back {to avoid spreading terminals] probe the two thinner wires and observe voltage while key on engine idling select low through to high stopping at each spot for say 10 seconds and note voltage and report. you might see a gradual shift in voltage from low to high speed. dont bother with the auto position.

[TimboTheKiwi]

Thanks Donald - will perform what you have described at report back - it mite be a couple of days - need to replace a hot water cylinder which has started leaking dammit!!

Cheers for the help