My high speed does not work on my fan blower. I have power coming out of the relay on the left front fender and the fuse is good. Have voltage to the yellow wire leading to the fire wall. The off and three low speeds work on the console. Any ideas. Could it be just a switch replacement. Thanks for any feedback.

 

Hi Greg,
First post, NICE!!!
There's a blower resister mounted on the heater air box under the dash that's part of the blower/switch wiring. Could that be your problem.
I'm too un-electrical to know how to check it so hopefully someone who knows will chime in.
Good Luck!
Regards,
Alan

 

Hi and welcome to C/F.
On my 74 there is a seperate fuse for the high speed fan. The fuse is in line and located under the drivers fender near the master cylinder.
Regards Pete.

 

Could be the high blow relay,check the dk blue at the relay for power with switch in high position,if you have power check the relay for ground,if you have both the relay is most likely bad.

 

Rodger
I have a ground (black). The orange is hot into the new relay. The wires were all fried together. The dark blue to the console switch is dead. There is no power to the purple and I am not sure where it goes.
Need help thanks.

 

Greg,

Wow.. we just did one of these in our shop Friday.. Roger.. you remember the car.. the gourndless wonder.. But it's still pretty fresh.. so here goes.. I hope..

The orange wire is your high blower speed main power feed wire and is fused on the passenger side of the car as indicated by 74.

In most cases when you don't have high blow, you have either a wire off (melted terminal connector) at the high blower relay, a defective high blower relay, defective console switch or the orange wire fuse is blown.

The high blower orange wire fuse can blow and Pete's diagram shows exactly where to find it too... If the connectors on the high blower relay go bad and the wires touch there is a good chance the fuse will also be fried.

The purple wire runs to the blower motor and where the power on this wire comes from is determined by the position of the console switch.

So in a nut shell from off the cuff (and it's late so someone correct me if I'm wrong, tomorrow I'll look at a schematic).

When you put your blower console switch in the Hi position, the power out of the switch powers up the dark blue wire... When the switch is in high speed you should not have power on the green, yellow or light blue wire only on the dark blue wire. This wire runs from the console switch straight to the high blower relay... and triggers the relay to go to the orange wire power which feeds the purple to the blower motor. So when in high blow.. The dark blue wire makes the relay switch.. It puts the power from the orange wire running in the relay to the purple wire that runs to the blower motor.....


So.. if the car were here with me..

I would put the console switch in Hi position.

I would test the dark blue wire at the relay for power.

I would test the orange wire for power at the relay.

If I didn't have (you said you did) power on the orange wire I would go to the fuse.

If I didn't have power on the dark blue wire I would go to the switch in the console.

If I have power on both the dark blue and the orange wires.. I would verify the ground for the relay and if this ground is good, then relay is defective.

If you test the console switch for voltage at the dark blue wire terminal there should be power on this terminal only in the high blow position and the dark blue wire must be hooked up to the switch for this current to pass to the relay.

If you don't have power on the dark blue wire terminal, then you may have a defective hi blower switch in the console. If you do have it at the switch terminal then test continuity between the relay connection and the dash switch connection. If you don't have continuity on this wire it is broke somewhere in between.

Again.. and 74, Roger.. if I've made a mistake correct me.. It will be noon before I can look at a schematic on this.

 

Very informative posts guys!!!! I am having the same issues with my A/C but now I know what and where to check. Just before our HOT Texas summer.

Thanks alot

 

Tall.. I've got a real nice schematic but not on this machine.. Maybe tomorrow I can post a copy of it..

 

That would be really cool anything would help.

Thanks alot

 

I don't mean to hijack this thread, but I checked my fuse and bingo that was it, we have high fan speed. I couldn't tell what the original fuse was, it was a 20 something and blown. I noticed on the 74 wire diagram it shows a 30 amp. Is this correct for a 1973 as well? The 30 amp works good but I don't want to start burning up wiring. My manual doesn't show any wiring diagram for a car with air so ???

Thanks

 

Roger and Willcox,

OK I'm not good with electrics. I do have a voltage tester with alligator clip and pointed probe. It has a little light when power is detected. So with ignition on and console switch on HI I pull the three-terminal connector and put the alligator clip on the male end of the dark blue terminal on the relay and probe the corresponding female side of the connector. If the light goes on I have power. The ground wire is separate from the connector. Doing the same male/female thing solely there I should see what? Power on the ground circuit? Or do I put the alligator clip on the dark blue relay male and probe the ground? For the latter if I get light does this mean the relay is bad?

If I have power on both the dark blue and the orange wires.. I would verify the ground for the relay and if this ground is good, then relay is defective.

How do you verify that the ground is good?

 

On reading about this last night I think I have figured out how the relay works. The dark blue wire from the console switch is activated by the HI setting and triggers an internal switch in the relay to let power flow from the orange, 30-amp wire drawing battery juice to the purple wire servicing the blower fan. Then the high-speed fan should operate. It does not. The internal relay switch is an old-fashioned mechanical points type and should emit an audible (and feelable) click when the above happens. It does not.

-I have replaced the 10/12 gauge wiring under the driver's fender and the 30-amp fuseholder. That should be OK.
-the first three fan speeds are OK.

I would still appreciate advice (as above) on the test procedures but I am pretty much convinced the relay is toast. Can I open it up and clean up the possibly burnt/corroded contact points? I am certainly not averse to spending $20.00 or so for a new relay but I am intrigued as to how things work.

 

Sorry Paul I just now saw your post. You are correct in how the relay works,blue wire trips the relay and feeds power from the orange to the purple.For this to happen the black wire on the relay must be grounded.
Here is how I generally do a quicky check.
Alligator clip to case of alternator (ground)
all connectors still in place
probe orange at relay-should be hot
turn ign key to on
fan switch to high
probe blue wire at relay-should be hot
probe purple at relay-should be hot if blower is running-probably not hot since you have no high blow
now probe the black wire connector at relay-sometimes the test light will provide a ground if the black wire does not and tick the relay and turn the high blow on-if this doesn't work , try running a temp ground from the back of the alt case to the black wire connector.

[ another way to test to see if something is grounded]
put the alligator clip on the large pos post on the back of alternator
now touch the probe to whatever your checking for ground-light will light if its grounded
so if you touch the engine block,valve cover,air cleaner,all these should make the test light light
In this case touch the probe to the black wire on the relay- if it lights,the relay should be grounded(providing the connection between wire and male spade is clean).
Bottom line I think you have already diagnosed your problem correctly-the relay is shot.

Paul if I didn't answer all the test questions , point out which ones and I'll do my best to answer those.

 

Roger,

Here are the results with alligator clip to case of alternator (connectors are mated on relay):
-ignition off, probe 12-gauge orange at relay, light goes on, there is power so I guess that 30-amp circuit is OK, power from battery
-ignition on, fan switch position HIGH, probe 18-gauge dark blue, light goes on, so there is power coming from the console switch
-ignition on, fan switch position HIGH, probe 12-gauge purple, no light so I guess no power
-ignition on, fan switch position HIGH, probe 16-gauge black ground, no light, not sure what that means?
-ignition on, fan switch HIGH, ran a wire from the ALT case to the black ground terminal on the relay, nothing happened?

Your method #2 for grounds with the probe alligator clip on the (+) post on the ALT:
-ignition off, probe black ground terminal, light goes on
-ignition on, fan switch position HIGH, probe black ground terminal, light goes on

(Despite what I have put in BF above I believe the relay is grounded??)

The lack of transfer of power from orange to purple and on to the fan leads me to the conclusion that the relay is history, defunct, kaput. If you agree I will pick up a new one next week. NAPA seems to have them.

Thanks for the step-by-step! Much appreciated.

 

From what you have reported the relay should have tripped and powered up the purple wire.
Sounds like the relay is toast.
Just for fun and to be sure the purple doesn't have any problems,
turn your blower to med and using the test light (alligator clip on ground)probe the purple-light should come on but dimmer than usual
one other little thing to try is pull the 3 wire connector off relay and jumper the orange to purple-fan should run on high even without key on

 

Both those tests proved positive so the purple wire circuit must be fine. I'll report back when I get the new relay.

This is a long weekend in Canada so it may take some time.

 

Turn car on, set blower to HIGH and ac to MAX. Ground out the terminal connected to the black wire on the high speed relay. The one next to the orange wire.

If the fan blows high, your issue is with the ground. If it doesn't, your issue is the switch.

 

I thought I had this sorted out. The MAX setting on A/C is for drawing inside air only (i.e. recycle). I do not know what this has to do with the fan blower relay and fan speed? You can use MAX A/C with medium fan speed.

What switch are you speaking of? The ground is there as per comments above.

From Driver's Manual

MAX - the system utilizes vehicle inside air only
NORM - only outside air flows through the system

 

Didn't you mean relay and not switch ?

 

I will follow my earlier instincts/results based on Roger's diagnosis tree and just buy a new relay. I can't figure out what volition is speaking of. The MAX setting on A/C is a vacuum, not electrical, control.