OK, just noticed that when I go to the far right (High) switch position, my ammeter pegs out to the right.  All the other position the needle barely moves.  I replaced the blower motor resistor, the one that fits inside the air plenum from the firewall, a couple of years ago.  Is that what is causing this?

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Nope....on "High", the resistor is not even in play. The high speed blower works strictly off of the high speed relay...it's a completely separate circuit. Does the gauge ever come back down, or does it stay pegged all the time with the blower on High?
If it stays pegged, I'd have to suspect the blower motor drawing too many amps, or the connector on the high speed relay being corroded. High speed relay should be mounted on the A/C evaporator box under the hood(if it has A/C). With no A/C it would still be mounted in the same general area.




|UPDATED|9/28/2012 2:44:49 PM (AZT)|/UPDATED|


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Joel Adams
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It stays pegged.  This just started happening.  I replaced the relay you show back in the early 2000's.  I'll have to check the wiring to make sure the plug hasn't fallen off.

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If it's blowin, the plug hasn't fallen off, but it may be loose, corroded, or might even be melted some. It's normal for the gauge to show a dis-charge when you first turn it on high, but the alt/regulator should make up for it, and bring it back to normal fairly quickly...unless the alternator/regulator isn't up to par.

The gauge staying pegged to the "Charge" side sure leans toward the blower simply drawing too many amps, and the alternator is trying to keep the output up high enough to overcome the draw....Really sounds more like a bad blower motor to me, but it can certainly be a bad connection, too.

Does it dim the headlights when you turn it on "High"?


|UPDATED|9/28/2012 7:55:22 PM (AZT)|/UPDATED|


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Joel Adams
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Like Adam's Apple said, the high speed circuit doesn't have a resistor in line.  It gets full voltage from the Orange wire that goes from the "High Speed Relay" over to the "Horn Relay" on the driver's side.  By the horn relay, there should be a fuse holder.  My '73 has a 30 amp fuse in it.  First off, see if your fuse is 30 Amp and not higher.  Then follow that orange wire from the fuse holder back to the high speed relay looking for worn off or missing insulation that might be allowing some current to flow to ground.  If everything is good, then you probably need a new blower motor.

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1973 BB 4-Speed Coupe Project Car

OK, here is what I found.  The 2 wire connecter that plugs onto the resistor that is on the SIDE of the blower motor plenum was unplugged.  Not the resistor that fits into the top of the housing (just under the relay in Joel's picture), but the one that fits into the side of the housing.  I had to take the passenger side gill off to get to it.  Unfortunately, when I tried to slide the connector onto the prongs, the whole inner part fell into the plenum.   I don't know what that resistor is called as the one on top I though was the Blower Motor resistor.  I don't think I can get the part out of the plenum.  It's there until someone, not me, has to replace the evaporator.  I may be able to take the blower out and get my hand down in there....maybe.  I tried fishing a magnet in there to no avail.  Also, I'm not finding this part in the two catalogs I've looked in so far.  I don't know what it is called.

I also have an orange wire with a round rubber connector cover just dangling around the blower motor.  Don't know what that goes to either.  There is a double wire connector plugged into the blower motor housing.

Will tinker with it some more later this week.




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I fished it out!!  Took the blower out and was able to get my magnet down there an get it.  It is some kind of sensor or transistor looking thingy.  It mounts right next to the cooling air tube for the blower motor.  I'll be yahooing the part number to find out what it is.

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Kinda sounds like a temp sensor, from the description....hmmm.
Doubt it has anything to do with the high speed blower issue, but who knows? Got a pic, maybe? OR post the part # on it? I can search the parts manual...


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Joel Adams
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Here is the part:





Here is where it goes, the hole on the left.  The hole on the right is for the blower motor cooling tube:




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Sure looks like a temp sensor, to me....but why does a '72 have that? Research time!

That, my friend, is the "Ambient Temperature Switch".


It would keep the compressor from coming on, but has nothing to do with the blower, best I can tell.

I'm gunna send ya a wiring diagram for the A/C system, in case you do not have one.


|UPDATED|10/2/2012 9:53:23 AM (AZT)|/UPDATED|


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Joel Adams
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Looks like I may have to try and glue mine back together.

http://corvetteparts.com/item/switch-heater-air-conditioning-ambient-temperature-sensor-1968-1973/?d=43801&itm=Switch




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Just found the part number in my 72 assembly manual.  3917359.

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I noticed in the link you posted, that that part is for '68-'73....interesting. Don't think I've ever even noticed one. Gotta look at my '73 AIM and see if it shows it, and if it's the same part #. I've seen them on other cars, but never noticed one on a Corvette...but then again..I've never looked for one, either!

http://corvetteparts.com/item/switch-heater-air-conditioning-ambient-temperature-sensor-1968-1973/?d=43801&itm=Switch



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Joel Adams
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OK, glued the silver button part back on to the black mounting plate with epoxy.  Put her all back together and it still pegs the ammeter right.  So I started feeling wires.  Followed the orange wire all the way back to the inline fuse to the horn relay.  The orange wire does not get hot.  The red wire from the horn relay to the inline fuse is pretty warm, and the inline fuse holder is hot to the touch.  Does this tell you electricians anything?  There is a 30 amp fuse in the holder. 

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Yes...it tells us there is too much resistance in that circuit. So, we're back to the blower motor drawing too many amps...
If you can dis-connect the blower motor, turn the blower switch to "High", and the gauge responds correctly/normally, the blower motor is the problem. IF, however, you disconnect the blower motor, and the gauge STILL pegs, there is a short int he blower motor/blower relay wiring.
My bet is on the blower motor....


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Joel Adams
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Pulled the power wire off the blower motor and the gauge needle never moves in any switch position (no deflection either way).  I guess that's means it's the blower motor.  Is their any way to fix this short of buying a new motor, or are they a throw away item?

'Nuther electrical question.  The Transmission Controlled Spark system is not on my car anymore but the wires are still there.  Should I jump these two wires together?  Or make sure that they don't touch each other.  Or does it even matter.  They look like they burned from heat or a short a long time ago (before I owned the car) and the exposed wires may be touching each other.


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Blower motor is a "replace" only item. Nothing you can do to repair one, that I know of. 
 One last-ditch effort check, before totally condemning it...make SURE the blower motor housing has a good ground. Run a separate ground wire to it from the frame, or engine..anywhere that you know will give it a good ground, and see if that makes any difference.
 The blower motor wiring on one of my Cads was melting, and was keeping the blower from working right all the time. I bought a new($$$$) motor for it, but never installed it. I found the ground circuit for the motor was just barely making any ground at the connector, and the wiring was getting extremely hot. I ran a new, separate ground wire to the connector directly from the engine block, and that solved that problem. I now have a brand new blower motor in stock, if I ever do need it....

As far as the TCS, if the timer is gone, jumping the wires at the connector will prolly give you full-time vacuum...all the time. You may not want that. The system was designed to only give full vacuum with the trans in 3rd/4th gears only on the 4 speed. The timer was used to "delay" the vacuum coming on for about 20-30 seconds after shifting into 3rd, or 4th. Some years, it only worked in 4th. With the system working, if you let the engine idle, you can put the shifter in 4th gear, and in a few seconds, the engine will idle up as the vacuum kicks in. It's a neat way to test to see if it actually works.


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Joel Adams
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I'll try the better ground thing.  As far as the TCS is concerned, it's all gone except for the wires.  No vacuum switch.  My distributor advance comes right off the carb.  I just don't know if it is OK if he wires are touching each other.


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I would assume none of the wires has voltage on them. If so, then it would be fine to leave them as they are. If you do see voltage, then just tape them up, and hide them somewhere. 

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Joel Adams
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Oh tay, ran a ground from the frame to the  F&#$(^%$ blower motor and it still pegs the ammeter on high.  So....where is the best place to buy a blower motor.  I know all the Corvette catalogs have them, but since it's a generic GM blower, can I get one at a generic price somewhere?

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I would think NAPA would prolly have one. The same basic blower motor was used up into the mid/late '80s....

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Joel Adams
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Well, just replaced the blower motor with an O'Rielly's $20 blower motor.  Did not fix the problem.  So what is drawing so many amps?  It wasn't doing this 2 months ago.  

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There HAS to be a draw there somewhere to create that much heat. IF the new blower motor did not lessen the amp draw, then there has to be a bad/corroded connection in that wiring, most likely place would be the in-line fuse/fuse holder.
The high speed relay gets it's main 12v source from that wire coming from the horn relay. The horn relay on these early cars is basically a junction box, a place to tap into a solid 12v source for other components of the car...the blower being one of those components. Make sure the connection AT the horn relay is clean, and tight. Then follow the wire all the way back to the high speed relay, looking for anything that don't look right...like swelled insulation, or melting. Take a GOOD look at the crimp connections on the in-line fuse holder...if there is any corrosion(green, or white chalky crap) there, that is a source of resistance in the circuit, and that will create heat. As a test, you may want to run a new wire from the horn relay back to the high speed relay, and see if that eliminates the amp draw. If it does not, then the only place left to go would be the alternator, or voltage regulator....


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Joel Adams
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Hey Grapevine, TX, Went 2 corvette central.com & found a complete motor 4 your 72. Go online & check it out.

I got one at O'Rielly's for 20 bucks.  Fits perfect.


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Here's another electrical question for us iliterettes.  If the blower is drawing 40 amps, why doesn't it blow the 30 amp fuse?  

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IF the blower motor IS drawing 40 amps, it WILL pop the fuse...unless you got a bad fuse, or mis-marked fuse. Are you just assuming it's pulling 40 amps because that's what the gauge is showing, or have you actually checked the draw? Don't take what the gauge says as what the blower is actually pulling...that's kinda misleading. If the blower were drawing that much amperage, the gauge would actually be going the other direction...towards the dis-charge side. It's starting to look like there may be either an alternator or voltage regulator issue.....

I wish we were a little closer...I'd run out there and help figure this thing out.....we just don't get out your way very often.

|UPDATED|10/15/2012 1:33:47 PM (AZT)|/UPDATED|


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Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

FIXED!  Mostly.

I took the horn relay off the car.  All of the connectors had some paint over spray or something similar on them.  So took some emery paper to all the connectors and the relay terminal.  Took the inline fuse connector apart and cleaned those contacts and put a new fuse in it.

Put it all back together and cranked up the car.  When I went to High, the blower quit blowing.  AAHHHHHHH!!

So, checked all connections and still no high.  .

Then I jiggled the wires to the blower relay, it went click and the blower came on high.  Woohoo!

Checked the ammeter and NO DEFLECTION!  Double Woohoo!!

When I jiggle the connector to the blower relay, it will click on and off.  So now I'll pull it off and check all of the connectors.

I could take the 20 dollar blower motor back to O'Rielly's, but I think I'll just leave it in the car.

I guess it was just bad connections.

Thanks for all the good advice.  Wonder what will be broken next week .


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Glad you found something, Gary!! Wow...what an ordeal, eh? I would suggest you try to find a new relay....those things will get hot inside, and start melting the Bakelite insulator on the bottom. That may be the real problem...the connections on the inside may be failing. You can pull the metal cover off and have a look-see, if you want...just to see if it is in the process of melting or not. If it looks good inside, then cleaning the terminals of the connector might be all ya need. You could also smell the bottom of the relay...if it smells like nasty melted plastic, I'd start looking for a replacement.

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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

"if it smells nasty, I'd start looking for a replacement."  

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1973 BB 4-Speed Coupe Project Car

I like how Chevy mounted it right above the exhaust manifold.  No heat there......not!


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