Jump to content

more AC blower wiring questions


Recommended Posts

i've been slowly fixing things on this car for a while now and i am starting to tackle some wiring issues. My blower motor does not work. I have found the two orange wires coming from the firewall. The larger one with the inline fuse goes to a 4 pin resistor along with 2 other wires on the 3 prong side and then a black ground on the one pin side.

The thinner orange wire shows on the wiring diagram that it should go to the same resistor and pin as the larger orange wire. But, mine was definitely not wired to that 4 pin resistor, it was wired to a separate 2 pin resistor which just has one pin on each side.  But i cant find what other wire would go to the other side of the smaller 2 pin resistor. I have another free wire that comes out of the firewall, but i cant really tell what color it is.

The wiring itself definitely has been HOT and i will be rewiring and installing new resistors once i figure out what goes where.

thanks for any help

IMG_1683.JPG

Link to post
Share on other sites

Doug, I believe you're working on a 1971 car. 71 & 72 cars had the anti-dieseling & blocking relays above the glove box.

The thinner (18 gauge) orange wire is a power feed from the underhood relay feed (from the underhood in-line fuse) to feed the anti-dieseling & blocking relays. It's the only thin orange wire in the system.

How does it all work?

The anti-dieseling relay sends power to the AC compressor for a few seconds after you turn the ignition key off to help stop the engine.

The blocking relay prevents the powered AC wire from back feeding into the ignition switch which would keep the ignition powered-and the engine running.

41 minutes ago, dcmoore2 said:

i've been slowly fixing things on this car for a while now and i am starting to tackle some wiring issues. My blower motor does not work. I have found the two orange wires coming from the firewall. The larger one with the inline fuse goes to a 4 pin resistor along with 2 other wires on the 3 prong side and then a black ground on the one pin side.

The thinner orange wire shows on the wiring diagram that it should go to the same resistor and pin as the larger orange wire. But, mine was definitely not wired to that 4 pin resistor, it was wired to a separate 2 pin resistor which just has one pin on each side.  But i cant find what other wire would go to the other side of the smaller 2 pin resistor. I have another free wire that comes out of the firewall, but i cant really tell what color it is.

It does sound like your harness has been hacked up so I would ignore what somebody else did and start over. There's an easy way to eliminate the anti-dieseling & blocking relays.

Here's the proper wiring diagram for this stuff.

7172AC full.JPG

Link to post
Share on other sites

Thanks - I have ordered a new blower motor relay along with the 3 prong plug. I will replace the blower motor relay and its wiring and the inline fuse to see where that gets me. I guess going to the Resistor next? Is there a diagram somewhere that would tell me what color wire to check, at what location, for when the blower switch is in each of its 4 speeds, to try and narrow down whether its a bad relay, switch, resistor or thermal switch ?  The blower motor is new.           Would that smaller orange wire, from the anti dieseling relay, being disconnected have anything to do with the blower motor not working?       I would also like to eliminate the anti-dieseling. I assume since I now have electronic ignition, I wouldn't need to worry about dieseling - correct?

Link to post
Share on other sites

The tan, light blue and yellow wires from the blower speed switch each feed power into one of the resistors. Each resistor is then tied together and comes out of the resistor connector as a dark blue wire which splices in the harness to the blower motor wire.

When you go to high speed, none of the resistors are powered. A dark blue wire from the blower speed switch sends power to the coil in the underhood blower relay which closes and sends full power to the motor.

In low, low medium and medium, the motor, through the blower speed switch and resistors, is powered from the dash fuse block heater/AC fuse. When in high speed, it's powered from the relay which has the separate underhood fuse fed from the horn relay buss.

Question for you: Are the four wires in the resistor plug or has the plug been cut away and you just have four loose wires?

AC resistor.jpg

Link to post
Share on other sites

Cheap gas caused engine run-on, also known as dieseling. GM set idle speeds on cars with AC a little higher so they wouldn't stall when the AC compressor kicked in. This caused the engine to sometimes run on when the key was shut off. Their cure was to turn on the AC clutch for a few seconds when the key was turned to off. The load of the compressor stopped the engine. Again, this was for 1971 & 1972 cars, not 1970 cars.

If you don't think you need this feature, it's easy to bypass.

The relays and wiring are under the dash above the glove box. Looking at the diagram below, cut the wires marked with an X and splice together the light blue and tan wires. Tape off the cut wire ends.

The bolt that holds the relays in place also connects the lower dash to a body brace so if you remove the relays, put the bolt back in the metalwork.

7172AC RELAY DELETE.jpg

Link to post
Share on other sites
On 4/29/2020 at 10:52 AM, dcmoore2 said:

Thanks - I have ordered a new blower motor relay along with the 3 prong plug. I will replace the blower motor relay and its wiring and the inline fuse to see where that gets me. I guess going to the Resistor next? Is there a diagram somewhere that would tell me what color wire to check, at what location, for when the blower switch is in each of its 4 speeds, to try and narrow down whether its a bad relay, switch, resistor or thermal switch ?  The blower motor is new.           Would that smaller orange wire, from the anti dieseling relay, being disconnected have anything to do with the blower motor not working?       I would also like to eliminate the anti-dieseling. I assume since I now have electronic ignition, I wouldn't need to worry about dieseling - correct?

you asked if the 4 wires are in the resistor? Those are the G, LB, Y & DB - correct? if so, then yes, those are still wired properly to the resistor. excuse my ignorance between relay and resistor.  i appear to have a different set up for the relay. The above diagram shows both orange wires going to that relay, mine has the smaller orange wire going to a separate smaller relay. My big relay just has the large fused orange, PPL & DB on the one side then black to the other side. I will be bypassing the anti dieseling stuff also. Thanks again for the help.

Link to post
Share on other sites
  • 3 weeks later...

You should be able to test the motor with a test probe (or jumper wire) hooked to the positive side of the battery. Just poke it onto a connection where the purple wire is hooked to the relay. This should get a response from the motor. At least if you know the motor will run, you can work backwards to find out which item is failing to send power to the blower.

If I remember correct, (hmm)...the resistors are actually inside the suitcase where circulating air can keep them cool? I've never seen them go bad; they are pretty heavy duty. Their job is to drop the voltage that is sent to the blower to provide lower speeds. On high speed, the resistors are bypassed and not used at all. The regulator does the switching between the "resistor circuit for less than high speed", and the "damn the resistors full speed ahead" modes.

Link to post
Share on other sites
On 5/22/2020 at 6:17 PM, wallaby said:

You should be able to test the motor with a test probe (or jumper wire) hooked to the positive side of the battery. Just poke it onto a connection where the purple wire is hooked to the relay. This should get a response from the motor. At least if you know the motor will run, you can work backwards to find out which item is failing to send power to the blower.

If I remember correct, (hmm)...the resistors are actually inside the suitcase where circulating air can keep them cool? I've never seen them go bad; they are pretty heavy duty. Their job is to drop the voltage that is sent to the blower to provide lower speeds. On high speed, the resistors are bypassed and not used at all. The regulator does the switching between the "resistor circuit for less than high speed", and the "damn the resistors full speed ahead" modes.

thanks - nice car too....i finally got mine done after almost 3 years...

IMG_1696.JPG

IMG_1697.JPG

Link to post
Share on other sites
  • 2 weeks later...

should the small orange fused wire be hot all the time?

the blower motor works great when jumped.

i spliced in a new plug and installed a new relay.

i now have some fan movement on the 2nd and 3rd click of the blower switch.

nothing on low and nothing on high.

my next plan is to replace the blower switch inside.

Link to post
Share on other sites

well, the low speed runs all the time when the key is on. Not sure if it is the orange wire or not. I hated that function and unhooked my low speed so that position on the switch became "off"

 

Link to post
Share on other sites

Douglas, at the underhood blower relay, the 18 gauge orange wire is connected to the 10 gauge wire from the underhood fuse feeding the plug for the relay. This splice is in the relay's plug crimp. As the 10 gauge wire is hot all the time, so is the 18 gauge orange wire going back into the dash via the cowl grommet. Yes, this makes this skinny little wire protected by a 30 amp fuse.

This gives power to the anti-dieseling & blocking relays after the ignition key is turned to off and allows the relays to do their thing-which is to turn on the compressor for a few seconds to stop the engine.

1970 cars didn't have any of this and I'm not sure about 1972 cars. Correct wiring diagrams for 1972 cars are hard to come by.

Link to post
Share on other sites
  • 1 month later...

OK - so i have replaced the blower switch. It along with the wires were burned and definitely contributed to my issues. Now I have all fan speeds EXCEPT high.  Mine is different than what i see in the diagram because i had two relays on the firewall and an orange wire went into each of them. Unlike that diagram that shows both orange wires going to the same relay. I'm not sure if that had been hacked by previous owner but that is how i got it. But i think the anti dieseling crap is confusing me now........  I'll check to see if i have both orange wires or at least the hot one that comes from the horn relay connected into the relay on the firewall, which is new but it may be wired differently....and it is starting to make sense now. I will wire it the way the diagram shows, which actually just ties both orange wires together. If I dont hook up the anti dieseling orange wire into that relay, will that somehow keep something else from working downstream?     

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...