|
|
|
The passenger compartment heater/AC fan in my '94 850 sedan works fine. However, the expensive resistor, Volvo part #9137937, that varies the voltage for speeds 1-3 has just died again within days of being replaced. That resistor has a single-use thermal fuse, which has now blown.
Here are my questions
1. Is the fuse really set for 216 degrees C as its markings imply?
2. Anybody know of a source for replacement fuses? They have GOT to be cheaper than $57 (lowest price I found online).
3. Any reason why I should not just jumper across the thermal fuse? (Yeah, I know this might be silly, but it seems to me that there is little reason why a component IN THE CABIN A/C airstream should EVER get that hot.)
4. Any reason why I should not put an external DC current fuse holder in place of the thermal fuse so that I can experiment with various amperage fuses as protection? And the motor already has its own fuse...
5. Might the Volvo part be faulty?
and finally,
6. Any reason why my electrical system should be putting out enough current to fry the heater resistor thermal fuse in the first place? As I remember from high school electricity, resistors absorb current by turning them into heat. More current or voltage, more heat. Since my resistor's thermal fuse failed, might that mean that the resistor is sinking more current and hence getting too hot.
Thanks.
|
|
-
posted by
someone claiming to be dave
on
Tue Oct 24 17:08 CST 2006 [ RELATED]
|
|
Even without my experiences with failing blower motor bearings, I'd say that the likeliest cause for the thermal fuse blowing is because it's getting too hot, from drawing too much current, from the motor having to work too hard.
When it rains hard, water infiltrates my car via the cabin air intake filter (which gets soaked). Water can wind up on the floor in the passenger footwell. Since this can also freak out the motor, I assume the motor (shaft/bearings) also gets wet, which may explain my accelerated experiences with re-re-re-lubricating the bearings.
My car has the ECC, and when the blower motor's unhappy, the REC/AC lights blink upon powering up or turning the engine off. It's done that so many times now that I don't pay much attention to it any more. (Ah, the joys of owning an older car.)
- Dave; '95 854T, 182K mi
|
|
-
|
|
|
I just realized yesterday that the same thing happened to me! I replaced my resistor pack with a genuine new one about 2 months ago one from eeuroparts (usually cheaper than FCP Groton) and it is already dead. Very frustrating. So check for a dirty evap unit or bad wiring? Any other ideas?
Maybe someone has some tips for getting that resistor pack in and out too. There was not enough clearance between the wall the resitor pack screws into and whatever's behind it (cabin side), where you access the screw. I had to force the old one out and the new one in and it was nearly impossible to unscrew that little torx screw. There must be an easier way, right? It's possible I damaged mine on the way in, causing it to fail early.
I'm all ears on this one. $50 for a few resistors and a fuse is crazy $$$. FCP Groton charges $71!
|
|
-
|
|
|
Radio Shack sells similar thermal fuses: $1.49 each in stock at both the stores I called. I replaced it last weekend and it seems to work fine. For a buck and a half I'm happy to replace the thing every so often.
You are right, there is not enough room to easily access the resistor without removing things. For my '94 and '95, I went in via the glove box:
1. Remove the arc-shaped arms that support the glove box door when open. The arms clip into the glove box door's back side.
2. Remove the glove box, which is held in by 6 screws. You might have to carefully pry the top down to get over the wire loop that the glove box lock engages.
3. Remove the trim panel under the console (over the passenger's feet).
4. Remove the knee bolster. It is a hefty-looking ridged piece of metal behind the trim panel. Held on by 3 13mm nuts. You can work it down and back to remove it.
5. Voila! You now have very clear access and sight-lines to the resistor, heater fan, relays, and heater fan wiring. Be careful of wires in orange bundles: this is airbag wiring and you don't want it to surprise you. Really you don't.
|
|
-
|
|
|
Ahh, it's that damn knee bolster. Thank you very much.
I saw a good description on Matthew's site as well for this removal.
I was very afraid of taking anything out because of the air bags. The Haynes manual doesn't say to remove the metal knee bolster, just "remove old one and insert new one." HA!
So I'll avoid the wires in orange bundles.
Is the thermal fuse on the resistor pack or somewhere else? I didn't look at it too closely when replacing it, and the old one is not in a convenient location to check right now, although I do still have it. Are you saying this is probably what failed and that you just replace that when it does, instead of the whole pack?
Thank you very much for your advice!
|
|
-
|
|
|
The repair itself is pretty simple. Sorry I can't post a picture (I don't have a digital camera).
Yes, the thermal fuse is in the resistor. After you have removed the resistor, look carefully at it. The resistor elements themselves are in the green ceramic block, oval in cross-section. You will notice a small metal can with wires sprouting from each end between the green ceramic block and the black plastic 5-sided panel which mounts to the air plenum. This is the thermal fuse. Mine had a stylish conical pink glass insulator at one end of the fuse can.
Carefully cut the wires close to the ends of the fuse can, then solder the replacement thermal fuse to these wires. Position the thermal fuse between the green ceramic resistor and the black plastic 5-sided mounting panel. Take care that no wires extend beyond the outer perimeter of the mounting panel so that you can fit it back into the air plenum.
To be careful, you should test for correct electrical operation before reinstalling the resistor: plug the resistor back into the circuit, let it hang from the wires, then turn the ignition on (you don't have to start the car) and slide the fan speed switch on the AC controls. You should get fan operation in all positions. (When the thermal fuse has failed you will get fan operation only in the highest position -- which connects the fan directly to the battery/alternator voltage.)
Ah, last point: the resistor elements themselves are probably unserviceable.
Have fun! That $1.49 Radio Shack thermal fuse just saved you $70. Neat, eh?
|
|
-
|
|
|
Oh, I forgot to ask: Do you know the specs on the thermal fuse? If they're printed on the thing you don't need to bother looking them up, I can figure it out, but if not I'd like to make sure I get the right part. Thanks
|
|
-
|
|
|
The specs were (note the past tense) printed on the case, but I could not read them clearly. So I'm guessing at the rating. I think it read 216 C, but I could very easily be wrong.
|
|
-
|
|
|
Thanks a lot Benglar. I wish I'd done this the first time it died. After I got the part in the mail and was looking at it I said to myself, "This cost me $50?!?!?, I could build one myself!"
I might have a chance this weekend and I have a feeling it will work. If only I could figure out why it's failing...
Some people on Mathew's Volvo forum say that a dying fan drawing higher than normal current might cause the resistor pack to die. It's a common problem with the ECC systems, even though mine is manual. My fan sounds quiet and healthy though, when it works, so I think I'll try the $1.49 fix first.
Thanks again for such good instructions.
|
|
-
posted by
someone claiming to be fixit2003
on
Tue Oct 10 04:42 CST 2006 [ RELATED]
|
|
I don't know if I'd recommend replaceing a thermal fuse with a current fuse. They're really designed to do two different things. When I replaced my evap unit recently I was really surprised at how big the heat sink was on this. Evidently there is alot of heat that needs to be dissipated and 216 deg C may not be too unrealistic. You may have a combination of low air flow due to a dirty evap unit and high blower current due to a worn armature. You may be able to look through the resistor hole and check the condition of the evap. Mine was in pretty sad shape. Plugged up alot w/ dirt, dust and leaves. If there's a part number on the thermal resistor try a Google search. You may get lucky. Maybe remove the fan and check inside with an angled mirror.
|
|
-
|
|
|
Thanks for the good suggestion. Might be why my wife complains that the fan does not move as much air as it used to.
Sigh: another chore for the weekend.
|
|
-
posted by
someone claiming to be ksg
on
Tue Oct 10 02:50 CST 2006 [ RELATED]
|
|
I would look carefully to rule out a short circuit - chafed wiring? water or some corrosive substance got in somehow? The resistor does indeed self-heat and might 'run away' by overheating itself, under excessive current draw. I'm thinking that if there's overcurrent or a short on the motor side of the resistor, the resistor might fuse before the main fuse blows.
|
|
|
|
|
