760 Heater fan

[blurp]

Hi all,

I noticed this morning that the heater fan is no longer doing anything. I have checked the fuse and replaced it but still no action. I can hear the servo operating the gate in the system and the AC and Recirc lights come on so I know the control panel is getting power. Changing the temperature setting has no effect.

My Haynes manual doesn't mention any, but is there a relay I can check? There was no prior warning, it always blew strong, so I have to assume this is something electrical. I haven't worked on anything in its vicinity so I wouldn't have disturbed any wiring.

Is it possible that a weak battery would cause this function to be sacrificed? Or is there a relay I can suspect?

Thanks!
blurp

 

[blurp]

Well I believe I've interpreted the wiring diagram in the back of the Haynes correctly to indicate that there IS a heater fan relay, but which one is it?

If anyone has any recommendations on identifying it I would appreciate them.

Thanks,
Blurp

 

[Peter K L Milnes]

Blurp, the fan is fed via a combination bank of resistors which provide the various speed settings for the fan. The unit is usually mounted in the fan ducting (for cooling purposes) and I expect that IPD or Groton could supply the part if it proves to be duff. The early ones were separately wound resistors looking like loops of barbed wire without the barbs. There are several types as this form of fan speed control is used throughout the Volvo model range. Later units (such as the ones for 900 series) use high power resistors (similar to the dropper resistors in an old style TV). Before 1988 the heater fan was fed by a relay under the dash, passenger side, mounted very close to the fan itself. Under the fan relay is the resistor unit, screwed into the ducting from the fan into the heater/aircon. 1988 and after the fan is fed via the ECC power stage, a small unit mounted on a finned heatsink, fitted to the ducting in a similar position to the resistor bank on pre '88 cars. There are two relays inside the power stage, one operates the full speed of the fan by bypassing the electronic variable speed control in the power stage. The controlling signals come from the ECC Control Unit, at top centre of the dash.

Sorry for the complicated answer, but you forgot to mention the Model Year of your car.

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).

"blurp" wrote:

Well I believe I've interpreted the wiring diagram in the back of the Haynes correctly to indicate that there IS a heater fan relay, but which one is it?

If anyone has any recommendations on identifying it I would appreciate them.

Thanks,
Blurp

 

[blurp]

Blurp, the fan is fed via a combination bank of resistors which provide the various speed settings for the fan. The unit is usually mounted in the fan ducting (for cooling purposes) and I expect that IPD or Groton could supply the part if it proves to be duff. The early ones were separately wound resistors looking like loops of barbed wire without the barbs. There are several types as this form of fan speed control is used throughout the Volvo model range. Later units (such as the ones for 900 series) use high power resistors (similar to the dropper resistors in an old style TV). Before 1988 the heater fan was fed by a relay under the dash, passenger side, mounted very close to the fan itself. Under the fan relay is the resistor unit, screwed into the ducting from the fan into the heater/aircon. 1988 and after the fan is fed via the ECC power stage, a small unit mounted on a finned heatsink, fitted to the ducting in a similar position to the resistor bank on pre '88 cars. There are two relays inside the power stage, one operates the full speed of the fan by bypassing the electronic variable speed control in the power stage. The controlling signals come from the ECC Control Unit, at top centre of the dash.

Sorry for the complicated answer, but you forgot to mention the Model Year of your car.

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).

Peter,

Thanks for your detailed response. As it happens my 760 is a 1988 model so the answer is in there. I will take a look for the ECC powerstage and associated relays. Your post seems to imply that a separate relay is for full power but, since I get no action from the fan at ANY setting (including full blast) can I assume that the relays are not at fault, or does the action of one control the other? Also, is there a method for diagnosing relays?

This system went from working great to not working at all between drives so my wife's suggestion that the fan motor is "burnt out" seems unlikely and an electrical interrupt needs to be found.

Any chance this might be related to some stupid computer fault? How about the control unit, are they fairly robust?

I had suspected that perhaps some wire or connection may have been disturbed when I was fiddling with the stereo connections and the casing of the yellow fuelpump relay did pop-off on one of these in-dash excursions. But subsequent handling of wires and connections, jiggling and re-plugging, have yeilded no response at all from the fan. Nothing. Not a sausage.

So I'll go check this stuff out at lunch time and get back here with my findings this afternoon.

Cheers!
blurp

 

[blurp]

Peter,

Thanks for your detailed response. As it happens my 760 is a 1988 model so the answer is in there. I will take a look for the ECC powerstage and associated relays. Your post seems to imply that a separate relay is for full power but, since I get no action from the fan at ANY setting (including full blast) can I assume that the relays are not at fault, or does the action of one control the other? Also, is there a method for diagnosing relays?

This system went from working great to not working at all between drives so my wife's suggestion that the fan motor is "burnt out" seems unlikely and an electrical interrupt needs to be found.

Any chance this might be related to some stupid computer fault? How about the control unit, are they fairly robust?

I had suspected that perhaps some wire or connection may have been disturbed when I was fiddling with the stereo connections and the casing of the yellow fuelpump relay did pop-off on one of these in-dash excursions. But subsequent handling of wires and connections, jiggling and re-plugging, have yeilded no response at all from the fan. Nothing. Not a sausage.

So I'll go check this stuff out at lunch time and get back here with my findings this afternoon.

Cheers!
blurp

Well I got in there at lunch, took the glove-box out so I could have a truly unobstructed view and was able to find nothing apparently wrong or out of place. I was also unable to locate anything resembling a finned heat-sink but I did find a small flat black box (approx 2"x3" and .5" thick, near the top of the fan housing) with 2 plugs attached to it: a 2-prong black (of which one wire is blue-black) and a 6-prong yellow (of which one wire is purple). The plug for the fan motor is powered by two wires: purple and blue-black... coincidence? Finally the thin black box I mentioned has a circular pattern of small holes, likely for cooling.

So have I found it? If so now what? I suspect I need to connect a volmeter across something to see if charge is even getting here but where do I test? I connected the voltmeter across the fan plug and no power is getting there at any setting.

Thanks,
blurp

 

[Peter K L Milnes]

That sounds very like it Blurp, if it looks similar to the base of a pyramid with two sloping sides. The heater fan supply is from fuse 28, which also feeds the fan speed controller. The ground for the fan is fed through the controller. The current path is from the battery via the common power connecter to fuse 28. Then via a 2-pin connector under dashboard to the fan, the speed controller and the ECC control unit on pin 21 of the large connector. The small connector is only for Water temperature, In-car temperature, Ambient Air temperature and Solar sensor. Check back from the fan supply connection at the fan, to the fuse. If that reveals where the lack of power lies then check for continuity on the two purple (Violet) lines for fan and controller and also the line to pin 21 of the control unit. As the ground goes through the speed controller you need all connectors connected to enable power to be measured. On the speed controller the Green/Yellow wire (pin 2) is the feed for the compressor clutch, which is fed via the pressure sensor ( mounted on the Condenser with a two-pin connector). There are no relays external to the system, the only relays being the two in the speed controller. There are six solenoid valves controlling the Vacuum Distribution (for the air-con)
and a Servo motor.

Keep at it buddy, you are almost there.

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).

 

[blurp]

Peter,

I read your message, then read it again. Then I scratched my head for a while, and then I read it again. There are many different pieces of info in there and I believe I was able to act on some of them. The observations gained today are as follows:

1. I have determined that 14v flow across fuse #28 so power is getting there.

2. I disconnected the power supply from the fan motor and hooked it up to my voltmeter and took readings as I switched through the various fan settings. I obtained the following readings:

key out 9.7v
Fan 0 8.6v
Fan 1 8.6v
Fan 2 8.6v
Fan 3 8.6v
Fan 4 10.8v
Fan 5 13.9v + CLICK

3. Upon switching to power setting 5 I can hear the bypass relay you mentioned previously click (opening or closing).

4. With the only 2-prong connector pulled from the power stage all readings are 0.0v BUT there is still a click when you go to 5

5. With the only 6-prong connector disconnected all readings are 0.1v and there is no click in switching to 5

So that's what I've found out so far. What does it all add up to? Does the lack of variability in voltage indicate some failure in the ECC control unit? Or pehaps a failure in the relay that controls that part of the power range? Or something else that I have failed to examine? It seems that power is getting to the fan but the fan does not spin because something controlling it is telling it not to (or the fan is burnt out). It occurs to me that I didn't check that 4" length of wire that actually connects the fan to the power but I can't imagine why it would be defective. Now that will nag me all afternoon.

I feel that we're pretty close to a conclusion but I lack the understanding to identify it.

Thanks again for all your help,
blurp

 

[Peter K L Milnes]

When testing for voltage readings it is essential to have the system fully connected up otherwise you will not make sense of the readings you obtain. For instance when you mention 14V across Fuse 28 that would make me think that fuse 28 is blown. If you take a small test lamp and place one end on ground then probe both sides of the fuse with the other lead the lamp will light on both sides of the fuse. This tells us that the fuse is OK. transferring the non-grounded lead to the Violet wire at the fan motor plug should also light the lamp, as should placing it on pin 1 of the six-pin connector on the speed controller, also pin 21 on the 30-pin connector at the rear of the air-con controller. Connecting it to pin 7 (Yellow/White wire) of the 30-pin connector should give a lit lamp which proves that fuse 10 is OK. Connecting it to pins 1 & 2 (Orange wires) of the 30-pin connector should give a lit lamp proving that fuse 19 is also OK. Transferring it to pin 1 (also Orange wire) of the solenoid valve unit should also give a lit lamp. The speed information feeds from pin 8 (Red/Black wire) to pin 4 of the six-pin connector on the speed controller unit. Pin 9 (Brown wire) of the 30-pin connector goes to pin 5 of the six-pin connector where it switches one of the relays which controls 12V to operate the air con compressor clutch from pin 2 (Green/Yellow wire) of the six-pin connector. Pin 22 (Blue/Red wire) of the 30-pin connector, switches the other relay (via pin 3 of the six-pin connector) in the speed controller which gives full speed operation of the fan corresponding with position 5. Pin 19 (Pink wire, 30-pin connector) gives feedback to the ECC controller using pin 1A (Blue/Black wire) on the 2-pin connector on speed controller (which is the ground side of the fan motor) which is directly connected to pin 6 of the six-pin connector. when the engine is running there is a feed from the alternator output via a Red wire to pin 20 of the 30-pin connector. Pins 3 & 4 (30-pin connector) and pin 2A (2-pin connector) all three are Black wires, are connected to Ground point 31/14 behind the relay mounting at bottom side of console.

Hint, with test meter across the connected fan plug you will get a voltage varying between 0V and Battery voltage depending on speed setting signal (pin 4 of six pin connector). 0V corresponds to max speed and Battery voltage will correspond to zero speed; (Meter positive connected to Violet wire, negative to Blue/Black wire).

Please keep up the feedback as it will help us both.

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).

 

[blurp]

OK, I've made a chart of all the places I need to stick the test light and I'll go and do that at lunch time today. I have visually inspected all the wiring and, unlike in my 240, all of it is in excellent condition, all supple and flexible, no crusty or broken connections, no cracked or worn connectors.

My overriding problem with some of the advice below is getting the test light or voltmeter into some of the spaces described once the system is "fully connected". For instance, "transferring the non-grounded lead to the Violet wire at the fan motor plug" seems impossible because of the tight fit of all the plugs, there's just no crack to try to jam in the test light. Similarly I cannot test the fuse jack without removing the fuse. The 14v at the fuse was measured with the fuse removed and the two pins of the voltmeter plugged into each of the open slots. I suppose I could partially remove the fuse and make contact with the exposed metal (?).

Since I believe that the power stage has been identified, is there any way to simply remove it and visually inspect the relays contained within to determine a fault?

I will post whatever findings I can obtain later today.

Thanks for your continued interest.

blurp

 

[blurp]

Today's test results with the system fully connected up:

Voltage ACROSS FUSE 28:
Could not check without removing fuse, fuse tested fine elsewhere

TEST LAMP PROBES:
BOTH SIDES OF THE FUSE
Both ends of fuse lit up

VIOLET WIRE AT THE FAN MOTOR PLUG
Test lamp lit up

PLACING IT ON PIN 1 OF THE SIX-PIN CONNECTOR ON THE SPEED CONTROLLER Test lamp lit up

PIN 21 ON THE 30-PIN CONNECTOR AT THE REAR OF THE AIR-CON CONTROLLER. Don't exactly know where this is but if it's on the back of the ECC then I have not removed it. NOT TESTED

CONNECTING IT TO PIN 7 (YELLOW/WHITE WIRE) OF THE 30-PIN CONNECTOR SHOULD GIVE A LIT LAMP WHICH PROVES THAT FUSE 10 IS OK. Fuse 10 is also instrument lights, which do work, proving fuse 10 is OK

CONNECTING IT TO PINS 1 & 2 (ORANGE WIRES) OF THE 30-PIN CONNECTOR SHOULD GIVE A LIT LAMP PROVING THAT FUSE 19 IS ALSO OK. Fuse 19 is also power mirrors, which do work, proving fuse 19 is OK

PIN 1 (ALSO ORANGE WIRE) OF THE SOLENOID VALVE UNIT
Test lamp lit up

PIN 8 (RED/BLACK WIRE) TO PIN 4 OF THE SIX-PIN CONNECTOR.
Yes

PIN 9 (BROWN WIRE) OF THE 30-PIN CONNECTOR GOES TO PIN 5 OF THE SIX-PIN CONNECTOR WHERE IT SWITCHES ONE OF THE RELAYS WHICH CONTROLS 12V TO OPERATE THE AIR CON COMPRESSOR CLUTCH FROM PIN 2 (GREEN/YELLOW WIRE) OF THE SIX-PIN CONNECTOR.
Tested at pin 5: Test lamp lit up weakly + audible click

PIN 22 (BLUE/RED WIRE) OF THE 30-PIN CONNECTOR, SWITCHES THE OTHER RELAY (VIA PIN 3 OF THE SIX-PIN CONNECTOR) IN THE SPEED CONTROLLER WHICH GIVES FULL SPEED OPERATION OF THE FAN CORRESPONDING WITH POSITION 5.
Tested at pin 3: Nothing with speed set to 5, otherwise test lamp lit up weakly + audible click

PIN 19 (PINK WIRE, 30-PIN CONNECTOR) GIVES FEEDBACK TO THE ECC CONTROLLER USING PIN 1A (BLUE/BLACK WIRE) ON THE 2-PIN CONNECTOR ON SPEED CONTROLLER (WHICH IS THE GROUND SIDE OF THE FAN MOTOR) WHICH IS DIRECTLY CONNECTED TO PIN 6 OF THE SIX-PIN CONNECTOR. Tested at pin 1a, 2a and pin 6: Nothing at any speed setting

HINT, WITH TEST METER ACROSS THE CONNECTED FAN PLUG YOU WILL GET A VOLTAGE VARYING BETWEEN 0V AND BATTERY VOLTAGE DEPENDING ON SPEED SETTING SIGNAL (PIN 4 OF SIX PIN CONNECTOR). 0V CORRESPONDS TO MAX SPEED AND BATTERY VOLTAGE WILL CORRESPOND TO ZERO SPEED; (METER POSITIVE CONNECTED TO VIOLET WIRE, NEGATIVE TO BLUE/BLACK WIRE). My results are the exact opposite:
Speed 0=0.1v; Speed 1=6.1v; Speed 2=7.4v; Speed 3=8.5v; Speed 4=9.5v; Speed 5=12.4v

So that's what I've discovered. To me the lack of response from the wire that gives feedback to the ECC and the other wire in that 2-prong connector seems most significant but I'm not sure why. I can hear some clicking in the power stage but without looking inside it's hard to say if it's one relay responding or two.

I eagerly await your assessment of this data.

Regards,
blurp

 

[Peter K L Milnes]

Will try to send you the relevant diagrams as attachments to your personal e-mail address within next couple of days.

Theoretically the fan will give full speed when 14V is across the fan wires. Thus as the ground portion of fan current is regulated to give speed of fan, fan will go fastest when 0V is on the Blue/Black wire as 14V will be on the Violet wire. This corresponds to position 5 and "defrost" (IIRC) when full speed is required of the fan. The two relays in the speed controller could be labelled as "Compressor Clutch" and "Defrost" if they were labelled on the diagrams, which Sod's law says they are not. It is difficult to see what should happen when referring to volt readings alone or test lamp indications alone.

See if it is clearer when I get the diagrams to you.

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).

 

[blurp]

Thanks Peter. Please send the email to <blurp at austinpark dot com>. I will be taking digital photos as well and posting them to a website.

Perhaps I should add that some months ago when I got the car, since I was hearing the fan but getting no air, I removed the evaporator which was gummed up solid and with it the drier under the hood. The compressor has not had a belt on it in the time that I've had the car. After this it has worked beautifully for about 8 months before the fan just stopped turning and we find ourselves here.

Based on your comment about the fan giving full speed, is there a way I could simply apply full power directly to the fan just to ensure it has the capacity to spin? Just as one might apply 12v to the window motor and bypass the switch. That would eliminate a suspect or identify the problem in one motion. Perhaps I should pull the fan motor out... I recall reading on the brickboard about someone getting something sucked in there when the recirc was on.

It should be so simple.

Thanks again,
blurp

 

[blurp]

I got the fan out. It's dusty but otherwise unobstructed and spins freely. Can I just apply 12v direct from the battery to it?

Thanks,
blurp

 

[Michael Pardee]

I got the fan out. It's dusty but otherwise unobstructed and spins freely. Can I just apply 12v direct from the battery to it?

Thanks,
blurp

Yes - it is a 12 volt motor.

Mike

 

[blurp]

Hooked 12v to the fan and it runs like a dream. Back to the drawing board!

So with the fan eliminated as a suspect and the belief that the wires themselves are in good condition and have been mostly undisturbed, it leaves us with the relays in the power stage and ECC control unit as possble points of failure.

Right?

blurb

 

[Peter K L Milnes]

Hopefully diagrams should have reached you and will be of use.

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).

 

[blurp]

Ok, I have looked at the diagrams ad-nauseum and, while I still have some facility with such diagrams, it's the process flow that has me a bit hung up.

To this end I have slapped together a web page that includes another wiring diagram I received (similar but not identical to the one Peter sent me) and lists my assumptions and what I tested.

http://home.eol.ca/~clubshub

Of special note is that at pin 7 of the 30-pin connector to the back of the ECC controller the test light DID NOT light BUT the fuse (#10) was tested and replaced and the other system that relies on that fuse (instrument lights) is working fine. Peter indicated that it should light but no dice. The diagram doesn't show what else this pin is connected to or what it feeds (except maybe that it powers the lighting of the dials when the instrument lights are on). Is its failure relevant?

The power stage is quite difficult to get to and I have it partially unscrewed but, considering how much more difficult it will be to reattach, I'm not sure if I'll be able to determine anything by removing it and not sure if it's worth the scored knuckles to remove if the relays contained therein are fine.

Next step suggestions? Corrections to my assumptions? Other things I might test?

Thanks for all your help,
blurp

 

[blurp]

("Why won't that guy with the heater fan problem just go away?")

Hi all,

The heater fan mystery persists. Over the weekend I examined the diagrams associated with the Power Stage unit and tried to eliminate the relays entirely by pulling the incoming wire and connecting it where the outgoing wire should go at the fan itself. For a better explanation of that please take a look at the bottom of the updated web page:

http://home.eol.ca/~clubshub/

So all of this is based on my interpretation of the diagrams (also detailed on the web page) and I don't know if I'm thinking right. If I am then I believe I have just eliminated the Power Stage as a point of error.

This leaves only the dashboard controller as a suspect. If I cannot rely on my results based on eliminating the Power Stage please let me know.

Thanks very much,
blurp

 

[John Robertson]

How about a dirty switch or a tired fuse or maybe a loose fuse .Has the fuse any discolouration around it so as to suggest over heating ?

 

[blurp]

I've checked the fuses, first by trying them in other applications, then by replacing them entirely. The system seems to respond to the action of the switch insofar as some voltage regulation is taking place, just seemingly not enough.

I've added a photo of the suspect part to the bottom of the page at home.eol.ca/~clubshub

I'm waiting to hear back from some scrappers re: that part. It's a pain to get at so haven't seen it on eBay, Groton doesn't carry it.

Dealer wants more for it than I paid for the whole car. LOL

Know anyone parting out a 88+ 760?

blurp