How do I fix my fan speed

Tiny
SHANEALLEN27
  • MEMBER
  • 1997 OLDSMOBILE BRAVADA
  • 16,800 MILES
My fan switch only lets me select two speeds for the motor 3rd and fourth but not 1st and 2nd I replaced the blower motor, and the blower motor resistor and still only speeds 3 and four but not 1 and 2 and I know its not the switch on the dash because I put that new too. What else could it be ( the relay?) And if so where is the realy and if its one of the three under the hood on passenger side just before the windshield wich one is it. You understand what im trying to ask here?
Do you
have the same problem?
Yes
No
Tuesday, December 20th, 2011 AT 5:14 AM

12 Replies

Tiny
CARADIODOC
  • EXPERT
What do you mean by "you can't select those two speeds"? The fan stops running on those two settings or you physically can't turn the switch to those selections?
Was this
answer
helpful?
Yes
No
Tuesday, December 20th, 2011 AT 5:22 AM
Tiny
SHANEALLEN27
  • MEMBER
Well like I said it only lets me select 3 and 4 meaning those are the only two that work meaning again the motor only works on those two speeds
Was this
answer
helpful?
Yes
No
Tuesday, December 20th, 2011 AT 3:02 PM
Tiny
CARADIODOC
  • EXPERT
Your terminology is really confusing, ("it only lets me select 3 and 4"), but I think I get your meaning that you CAN turn the switch to positions 1 and 2 but when you do the fan stops blowing any air. You CAN select those speeds, but the motor quits running on those two settings. I have to be sure so we're talking about the same symptoms and observations. You wouldn't believe how many times we have the wrong things in mind when we use our experience or training to come up with a plan of attack.

Based on those symptoms my first thought would have been the switch but since you replaced it already, we'll move on. By the way, did you replace the switch in an attempt to fix this problem or was it for something else that happened in the past?

Logic rules out the fan motor because it does run in some speeds. GM likes to use a relay but that is only for the highest speed which draws more current than the switch can handle on its own. Since the fan runs on the highest speed, we know the relay is okay.

After the switch, the next most common problem is the resistor assembly which you already replaced too. Did any of the symptoms change with the new one? There are two different resistor designs. One uses four different-value resistors, and one is switched in depending on the speed selected. A failed resistor will affect only that one speed, and all other ones will still work. The other design uses three identical resistors. All three are switched in for the lowest speed; two for the next speed, etc. That style can be wired in two different ways, with the common terminal going to the motor or to the switch. The operation will be the same but with a failure, the symptoms will be different. With the common going to the switch, like COULD be what's happening with yours, with a failed resistor, all of the speeds higher than the bad resistor will work and all of them lower, or before that bad resistor will be dead. If the switch is turned around and the common terminal goes to the motor, only the speeds lower than the bad resistor will work and the higher speeds will be dead.

Resistor assemblies also have a thermal fuse built in. They blow when they get hot from too much current or when there is insufficient air flow to cool the wire-wound resistor. Too much current is caused by a tight motor. You would have to measure that fuse with an ohm meter to see if that is what failed. Most fan motors get their current through a section of the ignition switch, and a lot of manufacturers have been having more switch problems than decades ago because they're making them cheaper and we have more toys and unnecessary computers that draw a lot of current and overheat the switch contacts and connector pins. A degraded connection will add undesirable resistance to the circuit which lowers the available voltage. It's backward to normal electrical theory, but a decrease in voltage will cause a motor to draw MORE current which can lead to repeated failure of that thermal fuse in the resistor assembly. That's why it would be helpful to know HOW the old resistor failed, (or if it actually had failed).

The next conclusion, if the switch and resistor are okay, is there are two broken wires between them. That is not likely except for two possibilities. One would be the wire harness is mispositioned and has fallen down onto a sharp metal bracket. Vibration will cause the wires to be cut on that bracket, but the clue would be one speed quit working first and the second speed quit months or years later. A more likely suspect would be the terminals in a connector overheated and the plastic body started to melt. That heat will migrate over to a second terminal and cause it to be degraded too.

If you can say with absolute certainty that both speeds quit at exactly the same time, I would be fairly confident you're going to find the problem to be in your new switch or resistor. If the two speeds quit within a few days or weeks of each other, I'd be leaning toward the switch. If you feel those aren't the cause, you're going to need a test light or a voltmeter to find the breaks in the circuit. I'll try to find a wiring diagram to walk you through the test steps.
Was this
answer
helpful?
Yes
No
+1
Tuesday, December 20th, 2011 AT 11:42 PM
Tiny
WRENCHTECH
  • EXPERT
It can only be the switch or the resister or the wires in between. Speeds 1, 2 and 3 all pass through the relay at rest and high powers the relay.
Was this
answer
helpful?
Yes
No
+1
Wednesday, December 21st, 2011 AT 12:15 AM
Tiny
SHANEALLEN27
  • MEMBER
Ok so that I am double and tripple checking my work and what not, where in the hell is the resistor. Like I said I am only wanting to make sure
Was this
answer
helpful?
Yes
No
Wednesday, December 21st, 2011 AT 12:32 AM
Tiny
WRENCHTECH
  • EXPERT
[quote]where in the hell is the resistor.[/Quote]

I thought you said you already changed it.
Was this
answer
helpful?
Yes
No
Wednesday, December 21st, 2011 AT 12:39 AM
Tiny
SHANEALLEN27
  • MEMBER
Yea I did just covering myself. But I am wondering if I have to drop my dash again to look for any loose wire connection or something because when I had my dash out awhile ago to fix the the air accuator motor above the heater core and then put the dash back together it seemed to work on the lowest two selections on the speed for my fan but only worked the following day and hasent worked since then. So could it be like I think and be a loose connection or misplaced ground or something under my dash then?
Was this
answer
helpful?
Yes
No
Thursday, December 22nd, 2011 AT 3:19 AM
Tiny
CARADIODOC
  • EXPERT
I'd suspect a connector that isn't fully seated. I think that would be more likely than a bad switch because it has four individual contacts, one for each speed, and it's not likely two would go bad. I'd expect to see one contact overheat and become arced and pitted, OR, ... The single common contact could be burned, but that would typically make all four speeds dead.

If any contacts in the switch are going to overheat, it's either going to be for the speed you use almost all the time, or it's going to be for "3". The lowest speed passes the lowest amount of current. The second speed passes a little more current. Speed 3 passes the most current of any of the contacts and is therefore the most likely one to burn up, unless like me, you never use that speed. The fastest speed is switched on with a relay to handle the high current, so that switch contact is under very little stress and not likely to fail.

There is also the common contact that switches between the individual speed contacts. If that one has overheated, the fan should not be working on any speed. So, if you can make sense out of all of that, I think you're going to find the plug is not fully seated in the switch, or a couple of pins got bent over. Bent pins happens to the best of us, but then the two lower speeds shouldn't have worked for one day.
Was this
answer
helpful?
Yes
No
+1
Thursday, December 22nd, 2011 AT 9:35 AM
Tiny
SHANEALLEN27
  • MEMBER
Ok cool thanks ill figure it out eventually lol. Another question seperate from this matter is I replaced both window washer pumps front and rear on the windshield washer fluid container because one wasnt working and the other was leaking from the pump itself, so in that case I thought they both would be working fine, the front works as it should but the rear washer pump doesnt and I cant even hear it kick on wich of course means no fluid on back window what are the things or thing that could be causing this to happen. And then another question is my OHC readings for like direction mainly and anything else are way off like it says I am facing south when in fact I am facing west and all the other setting like my mpg and all that I think are not fully reading correct either I dont think so could it be the computer unit itself up in the OHC or something else?
Was this
answer
helpful?
Yes
No
Thursday, December 22nd, 2011 AT 1:47 PM
Tiny
WRENCHTECH
  • EXPERT
You need to post the fix for the blower and start a new question for that other problem.
Was this
answer
helpful?
Yes
No
Thursday, December 22nd, 2011 AT 6:37 PM
Tiny
CARADIODOC
  • EXPERT
The reason for starting a new thread is that will give all of the other people a chance to see it and comment on it. By continuing the conversation here, only Wrenchtech and I will get automated e-mails telling us you posted a reply, and it will give us a direct link to it. No one else will read the new question.

In addition, I only know three things, and one happened to fit your first problem. There are three things that Wrenchtech doesn't know the answer to but someone else might. That said, I can offer a possible suggestion to your overhead unit. I have the same situation in my '88 Grand Caravan. First check if your display is set for the metric system. That will put everything in kilometers, liters, and Celsius. Mine is a basic unit with a metric / standard push button but newer ones require pressing a sequence of buttons to find the menu to make the change.

Chrysler had two, (at least), methods for adjusting the compass, and yours might be similar. Mine has two tiny holes in the module to insert a paper clip to press a pair of hidden calibration buttons. I'm supposed to face the van a certain direction, press one button, then face a different direction and press the second button. Newer models require you to drive in a circle three times in a parking lot. I can't remember if pressing any button is involved in the procedure. Some models also request that you enter a single digit number from a chart in the owner's manual for your area of the country. That is to adjust for the difference between true north and magnetic north.

I never bothered to adjust my compass so if I'm traveling out-of-state after dark, I have no idea which way I'm going. It would appear once it is calibrated, that will stay in memory when the battery is disconnected. Chrysler had a bunch of radio models in the '80s and early '90s that setting the clock was unnecessarily complicated, so a lot of customers stopped in to have a mechanic set it. I was never asked to reset or recalibrate a compass. If they did lose their memory, you'd think sooner or later someone would ask to have theirs reset.

All manufacturers do things somewhat similarly but there are a variety of procedures, so check your owner's manual for the correct compass calibration procedure. If no calibration is possible or required, look for anything magnetic nearby that can affect it. They don't use anything that physically rotates in the earth's magnetic field like a magnet. They use an electronic circuit called a Hall Effect device which is a transistor that turns on or off relative to how the magnetic field hits it. A magnetic mount CB antenna base will affect how those sensors work. A strobe light with pulsing high current will make a pulsing strong magnetic field when it's on but that shouldn't be a problem the rest of the time. The magnetic field from the motor in a motorized flashing light should not be strong enough to cause a problem.
Was this
answer
helpful?
Yes
No
Thursday, December 22nd, 2011 AT 8:50 PM
Tiny
WRENCHTECH
  • EXPERT
It also makes the question searchable from the archives.
Was this
answer
helpful?
Yes
No
Thursday, December 22nd, 2011 AT 9:38 PM

Please login or register to post a reply.

Recommended Guides