HVAC switch blows fuse but only in some settings

marknreimer · Jun 22, 2017

I've got a weird one here.

I have a 2008 Ranger Sport 4x4, new to me, 150K miles. When I bought it the blower didn't work. No big deal I figured. The owner told me about it up front and said his buddy had fixed it earlier, but it wasn't working again.

I checked the resistor - it was obviously new and recently replaced. Same with the pig tail, which appeared to have been installed nicely. It wasn't a hack job is my point. I checked the fuse under the hood, which checked out. Then I checked fuse #27 in the passenger side interior. I found a blown 10A fuse. The manual calls it the "Climate control blower relay/blend doors".

When I replaced the fuse, the blower fired up and worked at all speeds. Sweet! But as soon as I change the vent to anything other than the upper (IE: AC, MAX AC, upper and feet, feet only and defrost) the fuse instantly pops.

I can switch between OFF and UPPER at all speeds with no problem, with heat or ambient air. But any other location will blow the fuse.

It blows if I start the truck in any of those spots, and blows if I use the switch to change from upper to something else.

Any advice would be appreciated. I’m not great with electrical, but not so bad I can’t follow advise here. I’ve rewired some motorcycles, but that’s dead simple compared to a vehicle.

Thanks

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ericbphoto · Jun 22, 2017

Unplug your A/C compressor clutch ( 2-wire connector near front of compressor) and try your tests again. If fuse doesn't blow, clutch is bad. If I understand you correctly, all the switch positions that blow the fuse call for the compressor to run.

marknreimer · Jun 22, 2017

Ok I'll give it a try! The ONLY positions that don't blow the fuse are off and upper vents.

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marknreimer · Jun 22, 2017

Ok I unplugged the compressor and now my fan works in all spots. I did notice that when I change the dial to the foot position it just blows out the defrost. Is that because the compressor needs to be running in order to change the vent position?

What does this indicate? A bad compressor, or perhaps a short? Any suggestions for next testing steps?

Can I run it with the compressor not attached for now?

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adsm08 · Jun 22, 2017

Like ericbphoto said, you probably have an issue with the compressor field coil. The AC compressor has no bearing on your ability to select a particular mode for the air discharge, and it is perfectly safe to run the system with the compressor unplugged.

I would hook up a light bulb across that connector and try it again. If the fuse doesn't blow look into getting just a clutch and coil kit for the AC. It will be much less than replacing the whole compressor.

marknreimer · Jun 22, 2017

adsm08 said:
Like ericbphoto said, you probably have an issue with the compressor field coil. The AC compressor has no bearing on your ability to select a particular mode for the air discharge, and it is perfectly safe to run the system with the compressor unplugged.

I would hook up a light bulb across that connector and try it again. If the fuse doesn't blow look into getting just a clutch and coil kit for the AC. It will be much less than replacing the whole compressor.

Ok, so I hook up a 12v bulb and see if the fuse blows as a test? If it does not, clutch kit. If it does, move on to more testing.

Just to be sure I did it right, this is the connector I took off.

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marknreimer · Jun 22, 2017

Oh and second question - so the fact that I can't get the fan to blow at my feet only (instead it's full defrost), that is a totally separate issue??

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marknreimer · Jun 22, 2017

Thinking through this bit, why does the AC clutch activate when I move the vent position to defrost, as an example? I'm not blowing the fuse only when I activate AC. But I only retain the fuse with the compressor unplugged. So what role does the compressor play when you don't actually have the AC on?

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marknreimer · Jun 22, 2017

If this helps, I removed the blower relay (with AC plugged in) turned on the truck and the fuse did not blow in any position. The blower didn't run of course but does that help narrow it down?

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marknreimer · Jun 22, 2017

I replaced the relay and everything works now!! Only issue is that setting the vents to the floorboards still sends air to the defrost

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ericbphoto · Jun 22, 2017

Ok. First, I believe you unplugged the wrong connector. Below is a picture of my clutch connection. Yours should be similar and should be in a similar place near the front of the compressor. I think you unplugged a pressure switch, which also disabled the compressor.

The A/C runs in defrost/defog mode, to change the dew point of the air and remove moisture. The moisture condenses on the evaporator coil. Then the air is mixed with hot air from the heater core to warm it up again as hot, dry air for you windows.

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adsm08 · Jun 22, 2017

The AC activates in any position that involves defroster air flow because it makes the windshield defrosting more efficient if you blow dry air at it. One of the things AC does is dry air out.

Getting some air flow from the defroster vents in the floor position is normal, the way the duct work is built it has to happen that way. You can't seal the duct work completely the way that door sits. You should be getting air doing through BOTH.

ericbphoto · Jun 22, 2017

marknreimer said:
Oh and second question - so the fact that I can't get the fan to blow at my feet only (instead it's full defrost), that is a totally separate issue??

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That is a separate issue. That is controlled by things that are commonly called " blend doors" because they control the blend of hot and cold air, fresh or recirculated air and which vents blow. On older vehicles, they are controlled by mechanical cables, many newer vehicles use electrical motor operated doors. My old Mercedes uses vacuum operators. I'm not sure what year the change occurred in Rangers.

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ericbphoto · Jun 22, 2017

..... and adsm08 knows far more about Rangers than I do. So trust him.

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marknreimer · Jun 22, 2017

Thank you everyone for your help. It's been invaluable.

Eric - I did disconnect that wire first. The fuse still blew. Then I second guessed myself and disconnected the other wire at the back, as I pictured. That kept the fuse intact. At this point both wires were off. So I reattached the wire you are referring to, and the fuse was fine. So only by having the rear pigtail OFF could I retain my fuse.

Next I removed the relay with both compressor pigtails attached. With the ignition on I selected all the vent options. The fuse stayed intact. I replaced the relay with a new one and everything now works as it should.

I'm guessing my blend door issue is a totally different issue. It's not that important at the moment though. As long as the dash vents and the defrost work, I'm happy. AC is pumping cold air, heater works too.

I can't say I understand at all why a relay would cause this to happen though. Why would a relay create an overage when changing the vent selector knob to all locations except the dash vents!?

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HVAC switch blows fuse but only in some settings

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