Blower motor only functioning on high

[Franks944]

Hey guys, my 89 NA 944 Blower motor only functions on the highest setting (level 4). Does this sound like the blower motor resistor giving up on me? I checked it and saw a small amount of corrosion. I cleaned it to the best of my ability and still it only blows air at level 4, nothing before hand. Thanks in advance for the help!

[944 Ecology]

Try immersing it overnight in vinegar to remove corrosion.

[Monkey Wrench]

maybe you cna check the switch with an ohmmeter, I think ti changes resistance, idrect short is probably high if it goes through a resistor it increases the circuit resistance which lowers the current so it riuns slower..

not sure in porsch but in older volvos they had a great big ceramic wire wound resistor that was tapped for a few different resistances then motors became available that had more windings and I think the switch then selected or combined windings. if that type of fan motor was installed one would omit the wirewound resistor.. in my ford van it has some different resistance elements.

im not sure if the resistance coil is n the switch or maybe a separate part, others will know better.

a car with a non working fan is a non working car once you hit colder weather, because you cant clear the windows, immediately problematic.

[Franks944]

Thank you 944 Ecology and Monkey Wrench! I値l soak it first in vinegar overnight and see if that helps. I知 still not getting anything then I値l check the ohms and see if I have a wiring issue. If none of this helps, I知 going to just have to order a new one and hope it works!

[Jfrahm]

Best to pick open the thermal relay contacts with a sliver of wood or paper when you do this IMO.

[Monkey Wrench]

deoxit is the one spray that works, its a bit pricey, I uually get the little spray canand use it sparingly, I see they have a needle applicatoir now
https://caig.com/product/deoxit-d100l-25c/

vinnegar is cheaper

remember every circuit in the car depends on a good ground as well, It is easy to get fooled into thinking the positive supply is always the issue, but thats just half the circuit. in this case, a bad ground isn't going to make it always run full speed.

[Franks944]

@monkeywrench Yea I let it soak for 24 hours in vinegar and it did remove some corrosion. Used my wire brush again and it looked fairly clean but still the same result when I tried it. I値l check the ground too. By any chance do you know where the ground for the blower motor would run too? I know the car has multiple grounds throughout. The one by the headlight looks clean, battery ground is clean and the rear of the car ground looks good as well.

[Jfrahm]

A wire brush sounds too rough for those small bimetal thermal relays.
https://www.pelicanparts.com/techarticles/Porsche_944_Turbo/16-ELECT-Blower_Motor_Resistor_Replacement/16-ELECT-Blower_Motor_Resistor_Replacement.htm

[Monkey Wrench]

it doesn't looklike it has any moving parts, the pins just connect to the resistor, you could check it with a meter to see if the resistors are open.

it looks like the wires from the resistors connect to some brass parts, maybe crimped there as solder might melt the resistors are large because they are seeing a significant load ( high amps)

here's what a volvo 240 uses , you can google it for pics
Volvo: 1370240

if a resistor is open maybe you can sub in a volvo resistor or use a cermet resistor in its place?
( if you google cermet resistor you will see pictures of square resistors, they are generally made for higher load applications) they are made from ceramic material hence the name, cermet. one of those might work to replace a bad wire would resistor in there. If you want ot go into repairing the part.

we know the ohms, it was in the link, what we do not know is the maximum value( in ohms) of the coil wound resistors.

" The resistor values are shown on the wiring diagram in the manual: 0.25, 0.4, 1.0, 2.5 Ohms connected in series."


if you replce the resistor because it is open, then youd need to be concerned with the power rating of the resistor. if its is rated too high no problem, too low it will burn up. too large physically , maynot fit in the space .

how to connect it ? maybe a crimp ? that connection between the resitor and the plug in connector needs to carry quite high amperage. a solder joint could perhaps melt. it could be spot welded or crimped somehow, have a look?

it looks like these contacts on top may become corroded, not just the resistor the wires that plug onto that plug in thing might need some cleaning.. the wires there attach to a metal part, there you could possibly find an unnoticed bad connection.

in a car there are lots of those spade connectors, they are typically factory crimed onto the end of the wires, check there for signs of discoloration, if they look green you may have found an issue wiht a bad wire crimped connection.

I think with a meter, to check resistence of each winding, one could determine what is open there.

heres a handy tool, you can try that with vinegar or contact cleaner on it. most electronic stores carry them or ones like it, as the fibers break off you extend them. the glass fibers won't cause shorts.. stray brush fragments or steel wool can. a toothbrush might work ok. contact cleaner vinnegar sure, its is cheap, maybe alcohol.

https://www.amazon.ca/Hama-Fiberglass-Oxidation-Batteries-Electrical/dp/B00006IVJJ


its probably easier just to replace the part, sure..

it could likely be fixed if you encounter extreme pricing. I'd ohm it out, see where the break in continuity actually is, it may be a blown resistor, perhaps a bad connection. if the issue is a bad connection and not the part why drop 200 bucks or whatever it costs?

the ground location probably isn't so critical so if you suspect a bad ground just junp from the ground to a convenient ground location as a test, if that changes anything ( it should not) investigate the original ground..

if you like and it will reach just try using a battery cable and go from the battery negative to the wire location, then you have assured you provided a good ground. or clean the ground up. it won't hurt.

you can put the meter on ohms from the ground point it has to the battery negative should be very low resistance.

check across the battery, note the battery's voltage, now you can check across from any point that should have 12V to the negative terminal of the battery itself, it should be similar, if not you have resistance in the hot wire from the battery.

with the meter referenced to the ground post the other end should be the same or close to the same to the red or hot wire. ( as across the battery)

if you see less voltage then you have resistance between your red battery post and that hot location.

put a different way, you have a hot wire, it goes to various points and the wire should be low resistance, the wire itself has some resistance. if the power goes through a point of resistance like a bad connection then there is heat being dissipated by the connection.. and there you can measure a voltage drop ( when the circuit is in use)

picture that bad connector as a load, , it goes through the actual load ( the thing it runs) and back to ground. youd then have two resistances in series. there is a voltage drop at each resistance and they add up to the 12 V or what you read across the battery.

say for example that resistance is a bad crimp or a bad connection then you can find it by its voltage drop by following the circuit and checking the voltage at various points through the circuit back to ground..

a bad connection generates heat, heat can remove the temper ( springiness) from brass or bronze connectors and such parts. it can also cause blackening from any arc. that becomes a slippery slope as the connection can't improve itself and the bad connection means heat is produced and heat makes things worse not better. if spring tension is lost theat can harm the ability for the connector to work properly.

through any wire run, the wire itself has resistance, the wire itself produces heat but it should be negigable and not high enough to cause the wire to overheat and ruin its insulation.

if you have a direct short then yea the wire will burn off its insulation. a fuse will normally protect it from a melt down like that , if the circuit is engineered to be fused.

if the blower motor is fused and the fuse is making a bad connection this can be a problem as that alone can create resistance. this could slow the motor and also further damage the already bad connection at or near the fuse.

the fuse is in essence a little resistor, it is engineered not to fail with a normal load. it is engineered to fail if the load is excessive,
it is possible to measure across a fuse that is under load and you'd then see a voltage drop across the fuse. there are charts that can help determine what the load is, by knowing the voltage drop across the fuse.

keep in mind if you use these charts that the type of fuse is important and you need to be within the chart that matches the type of fuse that you are looking at.

with this, you can determine the load that is put upon a certain fuse or if that fuse is powering something with resistance. if the wire has a break there is no load across the fuse as it has gone open cuircuit then, if the circuit can't complete its path it has no load as it is then open circuit.
no load , no voltage drop across the fuse. if it has load there is a voltage drop across the fuse.

this can be handy in troubleshooting becuause can determine then if the fuse is actually running anything just by putting meter probes across the fuse.

https://www.scribd.com/document/473107484/Fuse-Voltage-Drop-Chart-Mini-Fuse

if you replace the part and then find that the issue is actually not the fuse but maybe a bad wire connection then you wasted your money. thats why Id determine the actual cause if you can.

it could be a bad connection, it might be an open ( failed) resistor. maybe the switch itself could be to blame? following voltage drops through the circuit pathe and checking connections should determine the real cause.

shotgunning the part may or may not fix it. hard to tell until you know the actual cause. you can order one if it helps simplify things for you.

[Monkey Wrench]

ok I missed the thermal resistors, so there are moving parts,probably a bimetal strip there and a contact point.

with relays and such those contacts may be plated with silver? so if you clean them tye may fail more quickly next time.

If I want to clean relay contacts Il fold a tiny strip of 400 grit sandpaper in half like about the size of a matchstick. put it between, apply pressure if you can, and pull the strip out, that fits the two surfaces so they conform..
Problem is, it wont replace any lost silver plating from the contacts. unit replacement with a new set of contacts might be more reliable. cleaning like that, may be a quick fix to resore operation.

I see what is happening now when the thermal strip gets hot it probably closes the contact allowing a speed change of the motor as compensation.. when it opens there is a spark after time, the contacts erode.

in a older volvo heat control is done by way of a thermocouple which affects flow through the heater core. there is a coil in the heat path, the end of the thermocouple is in a heat control regulator, normally operated by a choke type cable.

it seems porsche did it differently by regulating the fan speed? does a 944 regulate the water flow through the heater core?

a quick and dirty volvo heat regulator is a typical water tap installed in the rad hose to the heater core., you have to open the hood and turn the tap to regulate it, ok in a pinch, but not really correct. the thermal heat control can be a little expensive .. If its a beater, theres a cheap and dirty fix.
in a 944, I know it has heat control slider, does it have a ( choke style) cable that regulates the water flow through the rad?

[Franks944]

@monkeywrench, believe it or not, I did some work today on the 944 replacing a fan sensor along with some other little things. I went to start the car up and the blower motor started working on all speeds now! I guess the vinegar removed the corrosion enough and it just had to dry for longer, not fully sure how it happened but it痴 all functioning and I didn稚 have to spend $200 on a new one! A win in my book

[Monkey Wrench]

good probably bad cotacts, if it happens again you can still spend money ;-)