How to understand 60's/70's/80's GM blower motor circuits

These are all essentially the same with manual controls. Common problems such as no blower or only working on certain speeds can be easily repaired once you understand how the different devices operate.

[@fiveacredream8263]

Pretty amazing this video was posted 8 years ago and is still helping people out. Thanks, got my AC going again after this video.

[@gibbonsss8]

9 year old video. Thanks a TON, exactly what I needed

[@pontiacjeff]

Thanks... hearing you explain it helped me figure out how the high blow relay needs to be wired. I am replacing the old tin relay with a modern Bosch relay. For anyone else who needs it: 85- ground 86- orange wire from resistor 87- battery voltage (20a fused, 12g minimum) 87a- blue wire from resistor 30- blower motor

[@serpentza]

This was an incredibly useful video, thank you mate!

[@TylersNeighborhoodGarage]

I'm glad.

[@PipHopcom]

Brother I have a 77 Corvette and couldnt find ANYTHING to explain this system as clearly as you did... from so called EXPERTS! Bless you... YOU have solved MY problem! Salute

[@kevincrowley5064]

I just wanted to say thanks for taking the time to post these informational videos. I'm refurbishing my GMC G35 vandura at the moment and your clips are really helpful in understanding the basic principals of my vehicle. You have a very good way of describing things. So thanks!

[@RetroVintageItems27]

Your a really good teacher, very well explained and understandable.

[@TylersNeighborhoodGarage]

Thanks! It's not easy to explain this stuff sometimes.

[@michaelkantz3118]

Video is perfectly explained in terms I can understand, I replaced the resistor and blew it again putting my fan on high, so I replaced the motor and still don’t have high. Looks like I need to check the relay. So glad I found this video

[@JDirks2]

Nice job explaining how the blower wiring works. Very helpful.

[@demartinsm8479]

I'll get into the 68 today using your vid as a guide. Answered so many questions! Thank you!!

[@kentr287]

Thank you so much! I"m working on my 1980 Silverado that has a bunch of wires cut and missing. The manual does not show this detail - you saved me!

[@themdg]

Thank you for making this. It's very helpful as I look at what missing in my 78.

[@scratch187]

9 years later, video is still helpful - you are right - this is the same sytem on my 85 Camaro and my 79 Caddy. My Caddy keeps blowing those relays.

[@grandpahilljack1353]

Thanks for explaining this. I’m working on an 80 and the wiring has been hacked and butchered. The fan doesn’t try to work at all. This helps a ton.

[@robertduncan9669]

I have had college professors who could not explain their subject matter as well as you have done here. I'm going to call you Doctor fix it. Outstanding video explaining how this circuit for A/C works. im going to subscribe to you channel. Thanks a lot.

[@juacar812]

Working on a 1981 Chevy C10 and this helped a lot! Thanks

[@CamaroKris79]

I have a 79 Camaro (Rally Sport) and the dash switch had burnt out and broken up internally so i finally found original switch ($50 for the models with A/C) but the pigtail plug from dash wiring is a little boogered where it got hot. Keep loosing connection on med. 1 and med. 2 at my switch. If i can ever find a NOS pigtail for it I will be aces then LoL. Ive considered cutting it off and just splicing on female slide disconnects but for the sake of simplicity and originality i haven’t done it yet. Thanks for being good at what you do, because of your videos my quadrajet that left me on the side of the road is now 100% rebuilt and running like a champ! All 4 barrels are doing exactly what their suppose to do. Once again, thank you thank you thank you! Ive also put many quadrajet haters in their place because of what you have taught me LoL.

[@marcuskastanek7870]

Kris Denton what happened when the switch went bad? My blazer is blowing the fuse right after I turn those key, my best guess is the switch but I guess that why I’m here

[@GarthThomson]

Great video! Helped me improve my understanding of my C3 corvette system too. 👍

[@tonyinacay3652]

Best explanation on the wiring, Thank you!

[@swissarmychainsaw]

Tyler, thanks so much for your helpful videos. You are a good dude.

[@mustangmatt63]

Excellent explanation.. fixed my high speed blower after watching this ..thx

[@fastq7891]

Thank you, question, I have exactly the same truck, and I was assembling the relay wiring, the 10g wire that goes to the block junction box is not hooked up and fan works fine, any toughs on this? I know that this relay needs power but seems like it’s getting it from somewhere else

[@charlesmartin7347]

Well you just kicked stupid out the window and brought back common sense. Thanks for sharing your knowledge Fort Worth Texas appreciate you. Blessings and more blessings to you and your family

[@do6724]

Finally a video for vintage factory a/c. Thank you. I’ve been searching for a helpful video on this subject for a long time!

[@thefilmwave]

You have a teaching gift, glad you are using it productively

[@charliemartinez9461]

Awesome! I have been trying to get my heater to work for a while now and I’m so glad you had a great vid to explain it!

[@csgauss]

Thank you so much. This is exactly what I needed to know.

[@Lastactionhero101]

Great video, helped a lot. Working on my 77 c-20 and the whole ac system is getting a rebuild from scratch so this is helpful.

[@michaelcroston1274]

Thank you posting this, very helpful

[@richardracicot1982]

One other thing about those relays is that they also sometimes stay stuck on the on position with the blower running on max with the key out of the ignition and the heater controls on off quick fix is to tap the top of the relay till the contacs inside disconnect. Happen to me a couple of times with new and old relays in that same GM setup. Could save you alot of headaches trying to figure out because it did for me.

[@Transporter_Room_Three]

Thank you for this video. My wife's 1981 Pontiac Bonneville's AC just stopped blowing on high speed today, now we know where to start looking.

[@TheHumanSwissArmyKnife]

Even though this video is 8 years old, it helped me to finally understand that the blower motor was designed to be on low with the key on. It runs on LOW all the time.. OMG,!the hours I put into my 1979 GMC Caballero or El Camino, same basic layout. Now I can button her up and move on. Thank you very much. E The Swiss Army Knife

[@TylersNeighborhoodGarage]

Right, gm refers to that as flow-through ventilation or astro ventilation

[@lofstrand127]

Thanks for going through that so thoroughly!

[@herbsantiago3188]

thank you for blessing the world with this useful video.

[@MrJayo73]

I've unplugged the selector switch and made jumper wire to bypass the switch so I could hear the motor run on high but all I hear is the relay clicking. Do I have a bad selector switch and motor. Use to run on just low then not sure when but just stopped working all together. Any help would be appreciated thanks

[@thekawasakidude715]

Thankyou! This will help me out on my 81 k20 project. It's a wiring disaster

[@marshallmortensen752]

Is it possible to hook up a 3 speed/heater only control assembly (3 tabs on the back of the fan selector) to this same box in the bay (4 tabs on the resistor). I guess the only thing I'm bypassing is the hi-speed selection in the relay?

[@ronaldbrown4729]

Theres a few cables that coem fron the little black thing next to the blower motor can ya tell me where they go?

[@steelcityclassicsteelcityc1272]

Your video helped me out a lot bro,thanks for posting. 🖒🖒🖒

[@Rlowe928]

Any idea on why I would be getting power to all the wires on the resistor at once?

[@caddi70]

On my 70 Impala, which is basically the same as yours. My fan only works on meds hi. The switch, relay, fuse, and resistor is is good. I think, as far as resistor, I took it out and doesn't look burnt up. I've checked continuity and it passes. Can a resistor of this kind look good, but still be bad?

[@PapiDoesIt]

Thanks for the explanation. Mine turned out to be the switch itself, which is really a good thing because I didn't have to monkey around with the resistors.

[@robsenz.]

Thanks for this, defintely gave me an understanding of what to look for

[@lucasfisher6993]

Hey I’ve got a 1977 impala wagon. I need to test the ac pump so I want to force it to engage. But I can’t find a way to jump it to come on because there’s no pressure switch that I can see. I’d appreciate any help. Thanks

[@bookguitarguy]

Just a little tip, as far as electrical theory, voltage doesn't actually flow-it's only the current that flows (ie, electrons moving through the wire). Voltage is basically the difference in "potential" between the positive (12V) and ground (0v), and the amount of current that flows depends on the difference in voltage between the two points (12 volt difference), and the amount of resistance in the circuit (resistors, wires, and anything else in the circuit that resists the flow of the electrons). So basically, 12 volts doesn't "come in" to the motor, as voltage doesn't travel-it's only the current that flows (hence the rating of fuses in amps-which is a measure of the amount of current that the circuit can handle, before the wire would melt or catch fire). Hope that helps! Thanks for your videos, they're very informative, and I appreciate the friendly style as well

[@TylersNeighborhoodGarage]

Thanks for the tip!

[@bookguitarguy]

WhoSaidTyler You're welcome! And thanks again for the videos!!

[@ejm406]

Great video! Thanks!! How does the blower get power to always blow on low when the schematic shows the temp and a/c selector switches have a open on the input power from the fuse box when both are in the off (all the way left) position?

[@steelydan449]

Really informative, thanks

[@jahfiyah619]

Ok can i use any other truck blower motor for my 85 monte carlo ...is there any other blower motor campatable

[@williamlee6801]

Thanks for the detailed explanation. I have a question. The brown power wire at the connector behind the control switch in the dash gets extremely hot when running through the blower resistor at the 3 lower speeds.. It doesn't get hot when it's on high. The wire stays cool when it bypasses the resistor on full speed. It's only when running through the resistor that the problem occurs. I replaced the resistor and the wire still gets extremely hot. The air conditioning doesn't work because of a leak at the compressor. Any help would be greatly appreciated.

[@ksduathlete]

I put in an ac delete panel on my 1971 Monte Carlo. I cut a hole in new panel and took resistor off ac unit and installed . The dark blue wire is not connected and the tab where it goes is broken off. The fan doesn’t work at all. I’ve been working on this for days . Any thoughts? I can hear a springy noise coming from relay ( the first metal box) when I flip selector switch to high but yeah it doesn’t work at all now.

[@adamhenrichsen3794]

Super helpful video. Thanks!

[@dekebell3307]

Subscribed and liked. Thanks for sharing this info in a simple way.

[@KANDYPONTIAC78]

Hi, I have a quick question about my blower motor not running on high. When I switch it to high it clicks at the relay but doesn't do anything. I tried 2 new relays but still doing the same. Also I replaced the temperature control unit with a new one. Could you please give me your advice. It does work on first 3 speeds. Thanks for your help!

[@eusebiorodriguez4492]

From the 12v distribution block,there is a inline fuse on the orange wire that leads to the relay. What size amp should thay fuse be?

[@alansworld2484]

Wow he explained the whole circuit for heater made it sound easy great video.

[@DavidJWarEagle]

I have a 72 Riviera (w/ AC and manual temp control) and I have no low speed and no high speed but medium 1 and medium 2 work. Does that sound like a defective relay (no high speed) as well as a defective resistor (no low speed)? I still need to test the switch with my meter. Also, the "always on" low speed blower isn't working either.

[@TylersNeighborhoodGarage]

DavidJWarEagle Since you know the fan itself is operational, you can rule that out right away. Your next test will be with your meter at the resistor. In low you should have current provided to the resistor. In HIGH the current bypasses the resistor and goes straight to the fan motor. I am going to speculate that you have a bad fan switch. Keep us posted.

[@thegildedswampgirl658]

Please help need answers! I have a 79 Chevy Scottsdale C20 has AC I replace the blower motor I replace the resister ,the relay I’ve replaced the switch panel on the dashboard and what happens is when I turn the AC on and I turned it to Max AC it’ll come on sometimes and then sometimes The generator light will come on and it won’t blow at all and I switch it to vent fan comes on I’ve replaced fuses wiggled the fuse box and sometimes it come on and sometimes it won’t so I do not know what’s going on if you can help me I would be forever grateful

[@Tbales0950]

I need some help. My k20 81 has two selector switches one for my heater And one for ac. The ac one doesn’t work at all I found a burned fuse I replaced it and it turned on for a bit. Then blew. I disconnected the compresser wire and the fan doesn’t turn on at all I can turn the clutch and the pully spin

[@scotgarrett4448]

Very helpful! Thank you for sharing.

[@nstereo.]

Wow, great video! Thank you sir!

[@hunger997]

Watching this was that breakthrough moment that let me diagnose my car.

[@eusebiorodriguez4492]

Thank you so much for this video!

[@Ozsanti71]

Awesome video man. Thanks!

[@scottfinkner5648]

i have a 76 k10, i can hear blower motor running when truck is not running,. after starting and trying to turn fan speed up it does not go faster, no speed change. I dont know how to test ,where to start? Also my accumilater doesnt have that switch? on left side of it ,is that needed? thanks

[@jesserichards663]

I have a 79 c10 like yours fan works on low only I just got the truck two days ago and it’s cold, think you can help me out please?

[@stevencovington9508]

Where do you get replacement parts for the AC System. I have the similar setup in my Impala. My impala only runs on one speed!

[@TylersNeighborhoodGarage]

They are still commonly available from a parts store, Rock Auto or eBay.

[@ironmangolfer824]

Fantastic video. I needed this to fix my 87 v30. Thank you

[@TylersNeighborhoodGarage]

You're welcome!

[@frankfloyd6479]

When I turn the controls on the dash onto heat or air and go back outside to check my blower motor the negative and the hot are registering hot can you help me with this problem

[@80fordmustang6]

Question so I got my fan working in my 86 custom cruiser on all speeds but high when I go to high I can hear the relay click but I get nothing could that be that relay or should I dig deeper

[@middlesiderrider]

You should check the large red wire on the relay connector for 12v+. It should usually be connected to the junction block on the firewall. If it doesn't have 12v+ at the relay connector, it doesn't matter if the relay works or not, the fan won't run, because that's where it gets its high speed power

[@dmanshowto8193]

Great job explaining. My 79 TA is blowing the fuse under the dash when turned to high. I will be ordering a new relay I think.

[@kk-hp6ve]

My car isn't blowing hard enough should I change the relay?

[@Dragon-wh5tb]

Thanks you taught me a lot.

[@youngjj757]

Do u know the name of that purple plug I bought an 85 caprice and mice chewed it up.. ?

[@yogistylez]

You saved me hundreds....thx

[@frankfloyd6479]

That problem exists on a 1983 Monte Carlo when you turn the gauges on the dash to heat the blower motor positive and the negative are registering hot on a meter can you help me with this problem

[@wdonnelly7198]

Thanks, this should help me figure out my 1978 G20 blower resistor previous owner hack.

[@ej5088]

Thank you , very helpful !

[@wendellrountree4899]

I got power to the resistor and to the relay but nothing in the two wires going to the blower motor on a 79 trans am, so blower isnt working on any speed

[@2eagle86]

My 78 is the same way, my switches aren't working but it's idling at one speed, I put new ground a new blower and the switch worked before but it's a new blower but won't turn on high, how did you fix yours?

[@gregsilva1472]

Great video thanks

[@Lickxmyxkicks]

Having an issue with my 84, if I take a wire and connect the battery to the fan it runs just fine but soon as I connect the wiring harness with the fan to the relay it doesn’t come on at any speed. I took a multimeter and I’m getting 13 volts to the red wire on the harness. The fuse is fine as well. I’ve done tried 2 brand new relays and still can’t get anything going. I cleaned the grounds as well.

[@OKRODDER]

Any tips on what would cause the fuse to blow on the blower circuit? My first thought is a short in the circuit, or maybe a wire grounding out somewhere on the body.

[@TylersNeighborhoodGarage]

A multi-meter will be your friend on that problem. You can use it on the blower circuit to find whether you have a short to ground. Use the ohm setting, and connect one lead to the metal of the vehicle. Use the other probe and connect it to the side of the fuse holder that is NOT powered. If the meter goes from infinity to 0 resistance, you know you have a short. You can do that same trick for the wiring between the switch and resistor, and between resistor and blower motor. If no shorts then possibly the blower motor is dragging.

[@michaelclose7756]

super helpful video dude

[@daviddeacy8546]

How can you be contacted with questions? thx! ~ dave in denver

[@kingkonga245]

Which fuse it? Is it one of those metal case type fuses? My blower used to work on low, but now not at all even after replacing switch. Thinking it may be resistor.

[@MisterAdam-jj5jv]

Excellent video…valuable information

[@TylersNeighborhoodGarage]

Glad you liked it

[@gregthompson1339]

Where does the power to the A/C Pressure Switch come from.

[@sotatted22s]

Mines not working on high it only works on the 3 other settings I changed relay and resistor but the other 4 plug connectors that's on fire wall is missing on mines I think it's been removed or cut ...so how can I make it work with out it or what is it called so I can buy or get at yard

[@sotatted22s]

The junction thing with red wire

[@anthonywilson5561]

My relay is clicking when i unplug it but the switch ic not sending any power to the blower on 1985 iroc camaro

[@darrylwelch3970]

Thanks for the great information on your video. I am working on the A/C of my 69 Camaro. The firewall has been replaced before I became the owner. The blower works but that is about all. Is there somewhere I can find diagrams and Information on a Astro Ventilation system. I would be thankful.

[@eddieortiz8699]

Best explanation 👌. Thank you

[@TylersNeighborhoodGarage]

You are welcome

[@grantsomerville307]

If it has a bypass for all non-max blower power inputs until the coil is energized, I can assume it's an SPDT style relay?

[@boerenbrommer]

Thanks for this great video. I was replacing the speakers in my 1975 Cadillac Deville so I had to take the dashboard apart. After putting it back together, I realized the blower motor isn't working anymore when I put the key in. It only works on defrost now. What would cause such a situation? I'm guessing I messed up something when putting the dash back together, but I can't seem to figure it out.

[@carlbroomhall9665]

Well done looks much better and man ide love to be able to leave tools outside!! Leaving a car out front is questionable were I live 😅

[@jamesskinner1769]

A very good explaination of how this circuit all works. My problem is I have a 69 chevelle same wiring diagrahm with air cond. When I go down the road with the air on after about a half hour or so give or take 30 minutes it blows the fuse. Air is working fine which is drawing about 5 amps when running when I check the purple wire with the fan on high speed and the air on it will spike to about 18 amps. Could it be the resister or relay thats causing the blown fuse.

[@maxwebster7572]

unplug the blower does fuse still blow?

[@martinolivas319]

Hey brother I am having issues with my fuses popping when I turn my switch from the off position. I’ve put on a new relay and resistor as well as a new switch control. I’ve gotten it to run intermittently for about twenty minutes and then that fuse will go. I’ve disconnected the resistor all together and it’s working for now but the darn thing is new so I’m hoping that it’s bad out the box. How would I know if it is my issue causing fuses to blow?

[@KINGTBOOK]

Thank for the video!! But my 25amp ac/heat fuse keeps blowing... very sporadically. Might blow as soon as I turn my heat on, might last a few days! New blower motor and high speed relay.. what am I missing?

[@josem9409]

Did you ever figure this out? I cant place my fan on high.

[@brianjohnson8903]

I have a similar issue to what you're having I want to say it's just the switch because we did connected to the battery the blower motor works a little loose from its age but it does work what's the easiest way to remove the switch or do I have to replace the whole heater panel that's inside the cab on the dash

[@davidhatzenbuhler6888]

The blower speed switch can be removed from the mode/temp controls for replacement. AC and non AC use a different switch and there's at least one year break in the early 80's so you will not use a 76 switch on say an 86 truck. You should check the electrical connectors on the blower switch and the mode control switch to make sure they aren't crispy. GM used the same heater controls on their basic model cars so the blower switch and connector pigtails are still easily available.

[@jamesmooney8933]

The blower on '76 Buick Super required the left fender to be removed in order to replace the blower motor. The blow motor always ran, which shortened the life of the blower motor.

[@MrVjackson4328]

Ok, my resistor is on a 1973 grand am. My high and low won’t blow. 2 and 3 blow fine. My resistor has 5 prongs, not 4. How does that work?