Blower motor issues

[chev-obsession]

Recently I installed the factory A/C into my truck, when I turn the key on the blower motor comes on full blast and the switch for the blower will not control the blower. I used a factory replacement switch and wiring harness. I plugged the wire that goes into the fuse block into a constant hot which doesn’t seem right but that is the way I understand the factory service manual.

Do you guys have any suggestions?

[dmjlambert]

That sounds like a strange one. Something wrong with the wiring harness or a switch or relay I suppose.

Full speed only happens with the blower relay engaged. So something is causing the relay to engage when you turn on the ignition switch.

Unplug the fan under the hood. Turn the ignition switch on and find if you here the relay clicking on. The relay should only click on with the speed switch in the bottom position (bottom position is high, top position is fan off). Remove the plug from the back of the fan speed switch and see if anything changes regarding when the relay clicks on. Check the colors of the wires that go into the fan speed switch connector and see if they are in the right positions of the connector.

Here is a wiring diagram, not sure if it matches your model year, this one is 1969. I think the only thing different in later model years was the later model years have an anti-dieseling relay added.

[dmjlambert]

The 12 gauge orange wire plugs into the CIG position in the fuse panel. It has battery voltage all the time, but the voltage only goes through the relay to something when the relay is energized.

[chev-obsession]

Thanks for the help! I’ll do as you suggested tomorrow. I know I just have a purple wire going through the firewall to power the blower motor, the relay may not be grounded come to think of it. I’ll keep you posted

[Davidf]

Is the relay grounded?

[chev-obsession]

Ok, so I did some trouble shooting.

The blower motor and relay are grounded ( good grounds)

Checked the relay buy turning the key on and off as directed from above. No clicking noise was heard, put my hand on the relay and nothing was felt.

Checked the wires against the diagram, everything looked to match up.

I compared the new relay wiring terminal with an old wiring harness I have, it looks like the blue and orange wires were swapped. I swapped the wires and repeated the key on and off diagnosis. The fan would not turn on at all.

Unplugged the wiring connector from the back of the Fan switch. Blower motor kept running.

I did notice the ground on the firewall to the blower motor was getting warm.

I’m running out of ideas what it could be
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[chev-obsession]

So the top pic is from a spare box I had, the middle is the new wiring On the relay terminal. The bottom is the fuse panel how I have it hooked up.
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[dmjlambert]

The relay won't turn on if you don't have a wire connected here.
The relay should turn on with the key on and the fan switch in the all the way down position.

[dmjlambert]

Fan not running on either of the middle speeds may mean you have a problem with the wiring to the resistor or the resistor itself, inside the heater core box. That was a good find on the swapped relay wires. You probably fixed a problem by swapping them, but you still have other problems.

[RustyPile]

Originally Posted by chev-obsession

Ok, so I did some trouble shooting.

The blower motor and relay are grounded ( good grounds)

Checked the relay buy turning the key on and off as directed from above. No clicking noise was heard, put my hand on the relay and nothing was felt.

Checked the wires against the diagram, everything looked to match up.

I compared the new relay wiring terminal with an old wiring harness I have, it looks like the blue and orange wires were swapped. I swapped the wires and repeated the key on and off diagnosis. The fan would not turn on at all.

Unplugged the wiring connector from the back of the Fan switch. Blower motor kept running.

I did notice the ground on the firewall to the blower motor was getting warm.

I’m running out of ideas what it could be
Posted via Mobile Device

Switch those wires back like they were, that's probably not the problem..

No noise from the relay when switching on and off indicates relay is staying engaged.. Blower runs with switch harness disconnected eliminates switch as the problem.. You probably have a bad (stuck) relay..

[kwmech]

Where is the resistor pack?? should be in the housing

[dmjlambert]

resistors are in the heater core box

[dmjlambert]

Also, check your A/C fuse.

[chev-obsession]

Originally Posted by dmjlambert

The relay won't turn on if you don't have a wire connected here.
The relay should turn on with the key on and the fan switch in the all the way down position.

I understand that part, I was just showing the difference of the placing of the wires in the terminal going to the relay. The old box I had laying around isn’t in the truck. It was just for reference.
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[chev-obsession]

Originally Posted by RustyPile

Switch those wires back like they were, that's probably not the problem..

No noise from the relay when switching on and off indicates relay is staying engaged.. Blower runs with switch harness disconnected eliminates switch as the problem.. You probably have a bad (stuck) relay..

Switch the wires back how they were? The picture I showed of the new wiring is how I received the wiring harness. Comparing it to the old harness and relay I have, they are different.
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[chev-obsession]

Originally Posted by dmjlambert

Also, check your A/C fuse.

Crap there is no A/C fuse.... I’ll have to put one in tomorrow and see if that changes anything
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[dmjlambert]

I think you are almost there.

[HotWheelsFan]

.

Wires at relay:

Orange 12 gauge wire: Should have 12v positive at all times. This comes from fuse block (cig. connector receptacle), power comes from hazard fuse (15a).

Purple 12 gauge wire: Goes directly to fan blower motor. This is powers up the fan motor.

Dk. blue 14 gauge wire: Comes directly from blower motor resistor. This gets power through the resistor when fan switch turned on (low, medium, and high speeds).

Orange 18 gauge wire: Comes directly from fan blower motor switch. This gets power when switch is set to high speed.

Black 20 gauge wire: Is the ground for correct relay operation.


How this works is...

You should have continuity from the relay where purple wire and where the dk. blue wire connects to. This should have continuity at all times unless you energize the relay.

When you energize the relay the purple and orange connections should have continuity.

When you add power to the 18 gauge orange wire (when fan speed is set to high) and have the relay grounded, this energizes the relay allowing power from the cig terminal on fuse block to power the fan directly. This keep high amps from going through fan switch.

So, in order for correct operation the relay needs to be grounded, and 2 fuses in the fuse block must be good. 15 amp (hazard) and (A/C fuse 25 amp or Heater 10 amp). Fuse block labels can be confusing, A/C - heater fuse gets a 10 amp fuse unless vehicle is equipped with air conditioning, in that case it gets a 25 amp fuse. This is one fuse for both, and next to the radio fuse (3 amp).

If you check with a test light, ignition key off... You should have 12 volts at 12 gauge orange wire.

With key on and fan switch set to low, med, and high... You should have power at 14 gauge dk. blue wire (with some resistance as this comes from blower motor resistor). When fan switch is set to medium speed, testing will show the least resistance. When fan switch is set to low or high speed, test will show more resistance.

With key on and fan switch set to high... You should have power at 18 gauge orange wire (and still have power at 14 gauge dk. blue wire even though this is now bypassed from circuit).


As shown in the wiring diagram...

Fan blower switch gets power from A/C - Heater fuse (14 gauge brown wire, power with key on) and when switch is off no power gets through switch.

When fan is set to any speed ( low, med, and high) the 14 gauge yellow wire from switch get energized.

When fan is set to low speed speed, only the 14 gauge yellow wire from switch get energized.

When fan is set to medium speed the 16 gauge lt. blue wire from switch get energized, along with the yellow 14 gauge wire.

When fan is set to high speed the 18 gauge orange wire from switch get energized, along with the yellow 14 gauge wire.


Fuse Information

Two fuses are needed for correct A/C - heating system operation on the fuse block.

A/C - Heater Fuse: This is one fuse next to the "Radio" fuse slot. For vehicles with air conditioning a 25 amp fuse gets used. For vehicles with heater only, a 10 amp fuse gets used. This powers the blower fan switch and fan operation on low and medium speeds.

Hazard fuse: This powers the blower motor fan for high speed operation.

If you have no power to the fan switch with key on: Check the A/C - Heater fuse. If blower motor does not work on high speed, check the Hazard fuse.


I hope this adds a little clarification as I just rewired my A/C - heating blower switch and components this last weekend.

Bob

.

[chev-obsession]

So I cleaned the contacts on the air conditioning fuse holder and installed a fuse.

Nothing changed.

At this point, I’m thinking there has to be something wrong with the wiring or a faulty relay or resistor.

[dmjlambert]

HotWheelsFan gave a description of what you can expect on each wire for each switch position. Use a multimeter or lighted test probe on each wire to see the voltage situation at each wire. Connect the ground lead of the tester to a good clean metal ground, and the positive lead or probe tip to the fuse holder clip to make sure your fuse is actually passing voltage. You can also put the probe tip in the back of each connector where the wire enters to contact the metal of the terminal. Lighted test probes also have a sharp tip that you can use to piece the wire insulation.

[chev-obsession]

Alright I have fixed the issues I was having with the blower motor, with the help of RustyPile. He contacted me and was able to help me with the tremendous amount of knowledge and experience he has. He was kind and patient enough to explain and walk me through how the heater and air conditioning system works on these trucks. I will try my best to explain how we fixed the problem and what we found. This is long winded but hope it helps someone in the future. (RustyPile feel free to jump in anywhere and correct me if I’m wrong or didn’t explain something right)

Friday he calls me and explains how the entire AC and heating system works and with the given information, he thinks I need to verify that all of the wires and make sure all wires are in the correct spot and had a theory that the high speed relay was stuck or inoperable. The relay is a SPDT single pole double throw relay and it is normally closed.

Saturday morning I get a brand new relay, go home remove the old relay and the diverter box and hoses off to get to the resistor. Disassemble the old relay.... it looks like it sat at the bottom of the Pacific its whole life and think oh the new relay will surely solve this. So I Start probing and find that all wires through entire ac harness have continuity. While the harness is disconnected I swapped places of the big orange wire and dark blue wire on the relay side as I’m 90% sure they were installed incorrectly in the harness as I received it. Install the new relay and turn the key on, no fan on any speed. Swap the orange and dark blue wires back to the way I found them. At this point I’m out of daylight and patience.

Sunday I return RustyPile’s call from Saturday evening. I tell him what I did and what I found. He again walks me through how the system works and ends up at the theory that it’s the relay. His theory is the new relay I have is bad or it’s the wrong one. So we start troubleshooting. First we double check for voltage on both sides of the fuses on the ac and heater fuse which we did, then checked voltage at the brown wire going into the speed switch and voltage at the big orange wire at the relay. Voltage is good. Now we start troubleshooting the relay, it’s either bad or wrong one (no way... not a new Chinese made part)

So I remove the new relay, take it up to the battery on the truck and can’t get it to power up or hear it switching as it’s powered up. Bend the tabs up and remove the guts. RustyPile walks me through how to test it and to check for continuity while powered up. The relay starts working as it should when connected to power and ground. We verify with a continuity test while the relay is powered up, where exactly the big orange wire should go since we thought the big orange and dark blue wire were installed in the harness incorrectly. The big orange wire will have continuity with the purple wire (common spot on the relay) when the relay is powered up.

Reinstall the guts of the relay and make sure the metal tabs on the housing are tight against the phenolic part of the relay. Also swapped the big orange and dark blue wires yet again according to the position we indicated on the relay. Reinstalled the relay into the truck and reconnect all the wires throughout the system.

THE FAN WORKS ON ALL SPEED SETTINGS!!!!!!! I believe what happened was the relay ground on the phenolic base was not contacting the metal housing out of the new packaging. And the dark blue and orange wires were swapped in the harness when I received it. So I had two problems that are one of those “unlikely to happen” scenarios. It took some time to figure out and cannot thank RustyPile enough with his wealth of knowledge!

[chev-obsession]

You can see in the pictures the amount of rust and gunk in the original relay, even if it did work for $13 it was worth a piece of mind that it’s all new inside there.

[chev-obsession]

Originally Posted by HotWheelsFan

.

Wires at relay:

Orange 12 gauge wire: Should have 12v positive at all times. This comes from fuse block (cig. connector receptacle), power comes from hazard fuse (15a).

Purple 12 gauge wire: Goes directly to fan blower motor. This is powers up the fan motor.

Dk. blue 14 gauge wire: Comes directly from blower motor resistor. This gets power through the resistor when fan switch turned on (low, medium, and high speeds).

Orange 18 gauge wire: Comes directly from fan blower motor switch. This gets power when switch is set to high speed.

Black 20 gauge wire: Is the ground for correct relay operation.


How this works is...

You should have continuity from the relay where purple wire and where the dk. blue wire connects to. This should have continuity at all times unless you energize the relay.

When you energize the relay the purple and orange connections should have continuity.

When you add power to the 18 gauge orange wire (when fan speed is set to high) and have the relay grounded, this energizes the relay allowing power from the cig terminal on fuse block to power the fan directly. This keep high amps from going through fan switch.

So, in order for correct operation the relay needs to be grounded, and 2 fuses in the fuse block must be good. 15 amp (hazard) and (A/C fuse 25 amp or Heater 10 amp). Fuse block labels can be confusing, A/C - heater fuse gets a 10 amp fuse unless vehicle is equipped with air conditioning, in that case it gets a 25 amp fuse. This is one fuse for both, and next to the radio fuse (3 amp).

If you check with a test light, ignition key off... You should have 12 volts at 12 gauge orange wire.

With key on and fan switch set to low, med, and high... You should have power at 14 gauge dk. blue wire (with some resistance as this comes from blower motor resistor). When fan switch is set to medium speed, testing will show the least resistance. When fan switch is set to low or high speed, test will show more resistance.

With key on and fan switch set to high... You should have power at 18 gauge orange wire (and still have power at 14 gauge dk. blue wire even though this is now bypassed from circuit).


As shown in the wiring diagram...

Fan blower switch gets power from A/C - Heater fuse (14 gauge brown wire, power with key on) and when switch is off no power gets through switch.

When fan is set to any speed ( low, med, and high) the 14 gauge yellow wire from switch get energized.

When fan is set to low speed speed, only the 14 gauge yellow wire from switch get energized.

When fan is set to medium speed the 16 gauge lt. blue wire from switch get energized, along with the yellow 14 gauge wire.

When fan is set to high speed the 18 gauge orange wire from switch get energized, along with the yellow 14 gauge wire.


Fuse Information

Two fuses are needed for correct A/C - heating system operation on the fuse block.

A/C - Heater Fuse: This is one fuse next to the "Radio" fuse slot. For vehicles with air conditioning a 25 amp fuse gets used. For vehicles with heater only, a 10 amp fuse gets used. This powers the blower fan switch and fan operation on low and medium speeds.

Hazard fuse: This powers the blower motor fan for high speed operation.

If you have no power to the fan switch with key on: Check the A/C - Heater fuse. If blower motor does not work on high speed, check the Hazard fuse.


I hope this adds a little clarification as I just rewired my A/C - heating blower switch and components this last weekend.

Bob

.

Thanks for the info

[OliveK5]

This thread and the responses in it are super helpful - thank you so much to the original poster and everyone that contributed to this thread. I'll likely be outside sorting through this on my truck later this week.

One question I have is....and please hold your laughter.....where is the AC relay located? I've asked a few people and gotten a variety of answers - so I'm hoping you folks can point me in the right direction.

All the best,
Jim

[Andy4639]

Originally Posted by OliveK5

This thread and the responses in it are super helpful - thank you so much to the original poster and everyone that contributed to this thread. I'll likely be outside sorting through this on my truck later this week.

One question I have is....and please hold your laughter.....where is the AC relay located? I've asked a few people and gotten a variety of answers - so I'm hoping you folks can point me in the right direction.

All the best,
Jim

The relay should be mounted on passenger side of the air box under the dash. Under the glove box and should have a ground wire ran to it since it's attached to plastic housing.