A/C Blower Fan Issue
 

Recently, after converting over to R134A, my blower motor decided to only function in Low or High (or Max if you slid the control level from NORM to MAX. My '87 V30 has 4 positions on the fan speed control and all of them except for HI cause the fan to blow on LO setting. I have installed a new fan speed control switch as the original one was broken (Chrome button was ripped off).

I have searched and searched and haven't really seen any threads with the same symptoms as mine. Anyone have any ideas on where to look? I would just start replacing parts but I'd rather get some opinions first...
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Re: A/C Blower Fan Issue
 

Probably the blower motor resistor. If you have hi speed and any of the others are the problem....then it becomes a safe bet it's the resistor. Each speed below hi has to use the resistors in the pack before sending power to the blower. Hi sends full power to the blower. If you don't know it's attached to the top of the blower box in the engine bay with wires and a plug into the top of it.

Re: A/C Blower Fan Issue
 

Just replaced the resistor and no go...still doing the same thing.
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Re: A/C Blower Fan Issue
 

Just reading your post again. Basically you're saying you have 1st speed-Lo, 2nd speed-Lo, and 3rd speed Hi? If so, I would have to think something is funny with wiring. Each speed is supposed to be independent of each other. So if you lose a speed it doesn't default to low, or high, it just doesn't work period. But the others still will work at the correct speed. I would originally suspect the blower switch, but you've said this has been a problem with both of them. Anyone else work on the truck and possibly mess with wiring?

Re: A/C Blower Fan Issue
 

The truck has 56,000 original miles and a brand new switch...no one has worked on the truck and this failure just happened a couple weeks ago after I converted to R134A (it worked for a few days then failed), when A/C is on, the fam blows very low on LOW, MED, MED-HIGH and when I move the switch to HI, the fan blows HIGH (my truck has 4 positions on the fan speed lever). When I move to MAX A/C, the fan goes to MAX.
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Re: A/C Blower Fan Issue
 

Was thinking we had off as one of the settings on our trucks. Give me a bit to think, and I'll get back to you with some ideas.

Re: A/C Blower Fan Issue
 

I went ahead and three another blower fan speed switch into the truck to see if the new one I put in a couple months ago failed and the problem is still there...
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Re: A/C Blower Fan Issue
 

Your problem has me stumped. IMO, the only option is to start tracing/testing wires for the correct voltages. I personally would start with checking the wires at the resistor for voltage as they are easily accessible to test. You'd be testing the smaller wires there for battery voltage.
Brown/white should have power at lo.
Next speed up should be the tan wire.
Then next speed is the lt. blue wire.
The dark blue is the output from the resistor. It sends power to the blower relay when in speed 1, 2, or 3.
When in hi, the orange wire feeds to the blower relay which energizes the relay and offers full power to the blower.
Of the brown/white, tan, and light blue wires, only one wire at a time should have voltage.

Re: A/C Blower Fan Issue
 

Next time it happens, check for power at the resistor. If there is power, the ground is bad. I like to cut the blower motor ground and reroute it. I like to ground it on the alternator bracket.

Re: A/C Blower Fan Issue
 

Okay, so every single wire on the resistor harness has full voltage all the time, no matter which speed I set the blower motor switch to inside the cab.

I pulled the heavy purple wire from the blower motor itself and the test light was very dim on LO, MED, MED HI with no change between all three settings and then when I switch to HI, the test light goes full bright.

I am sorry but I don't have my multimeter handy right now, so I don't have specific voltages to report...
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Re: A/C Blower Fan Issue
 

Specific voltages aren't necessary. The fact you have full voltage at all the wires say that the problem is either the switch or the wiring between the switch. If it were me,my next step would be to unplug the fan switch and use a heavy gauge wire to jumper the pins at the connector together one at a time to see if the blower then changes speeds.

Re: A/C Blower Fan Issue
 

Doing this I found that at the fan switch on the dash, the orange wire is the power supply and all three other wires are the speed outputs.

No matter which wire I jumpered the orange wire to, the fan blows at HI speed.
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Re: A/C Blower Fan Issue
 

Looking thru diagrams to figure this out. Does the blower operate at all with the fan speed switch disconnected and the climate control on anything but off?

According to my diagram....brown/white should come from the climate control selector, and go out to both the fan switch, and the blower resistor, feeding the low speed.
So brown/white should be the power into the fan switch. This brown/white wire should feed the tan wire on speed 2, the light blue on speed 3, and the orange on speed 4.

Edit: Just figured it out typing the above info. Almost positive your blower relay is the problem!!! This causes the relay to never allow anything but the lowest speed, which actually comes from the selector switch NOT from the fan switch. IT also allows the high speed due to the high being on another circuit inside the blower relay.

Re: A/C Blower Fan Issue
 

No, with the fan speed switch disconnected at the dash, the blower does not operate at all!
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Re: A/C Blower Fan Issue
 

Thank you for your help, the relay was faulty! :) all better now!
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Re: A/C Blower Fan Issue
 

Glad I could help!

Re: A/C Blower Fan Issue
 

Hey, I have a 1984 chevy pickup and the blower motor does not go to maximum when I slide the switch over to max. The 3 speeds work fine. Does anyone know what the problem may be? Thanks...this is my first post!

Re: A/C Blower Fan Issue
 

Welcome to the site. The relay is bad or a wire is not making good contact. Remove the relay harness off the condensor box. Check the wiring. A relay is $8. At full speed, the fan receives 12 V. The resistor suppliers lower voltage for lower speeds.

Re: A/C Blower Fan Issue
 

I found this article on A/C also blowing fuses. http://forum.73-87chevytrucks.com/sm...c,26263.0.html

New relays have an internal resisitor which can cause problems.

Another common problem on blowing fuses is a bad clutch. Clutch coils can fail by drawing too many amps blowing fuses. A coil should take 5-7 amps to run.

Re: A/C Blower Fan Issue
 

Thanks, Mad Chemist. I will check the relay and wiring.

Re: A/C Blower Fan Issue
 

What would I troubleshoot if I only have HIGH in my factory AC truck? Where is the resistor if I have to troubleshoot there? I swapped my blower motor and only have high now

Re: A/C Blower Fan Issue
 

The circuit for resistor is faulty. The resistor is directly above the relay. The resistor bolts into the evaporator box. Check it for broken springs or connections.

Re: A/C Blower Fan Issue
 

If all else fails, wiggle the connector going to the fan switch on the HVAC control assembly. I had a bad harness connector going to that switch. AC Delco still sells a new harness for that application. In the heat of the desert I have had a lot of electrical connectors and harnesses wear out and need replacement.

Re: A/C Blower Fan Issue
 

Is it an a/c truck. Some of these ate vacuum controlled and have a vacuum hose by the box and distributor that needs to be hooked up
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Re: A/C Blower Fan Issue
 

Hey, thanks to everyone for their advice/tips. I actually traced the vacuum line to the damper door back to the engine compartment and found a check valve (?) installed backwards. I didn't know it was backwards but I turned it around and the damper door opens and I have maximum air.