High speed switch for fan blower
05-22-2011, 08:19 PM
#21
Race Director
In some years going to MAX will engage the high blow relay no matter where the blower speed switch is, I don't think your 74 operates that way. MAX is as you say just a vacuum control , and just closes the door to the outside.
In some years the black wire ground we have talking about is switchable, in other words the ground is applied or taken away as a secondary control to turn the relay on or off.
The one I can remember is 78 , if the rear window defogger is on the black wire ground goes away so the blower can't run on high at the same time the defogger is on.
In some years the black wire ground we have talking about is switchable, in other words the ground is applied or taken away as a secondary control to turn the relay on or off.
The one I can remember is 78 , if the rear window defogger is on the black wire ground goes away so the blower can't run on high at the same time the defogger is on.
05-22-2011, 08:53 PM
#23
Team Owner
In some years going to MAX will engage the high blow relay no matter where the blower speed switch is, I don't think your 74 operates that way. MAX is as you say just a vacuum control , and just closes the door to the outside.
In some years the black wire ground we have talking about is switchable, in other words the ground is applied or taken away as a secondary control to turn the relay on or off.
The one I can remember is 78 , if the rear window defogger is on the black wire ground goes away so the blower can't run on high at the same time the defogger is on.
In some years the black wire ground we have talking about is switchable, in other words the ground is applied or taken away as a secondary control to turn the relay on or off.
The one I can remember is 78 , if the rear window defogger is on the black wire ground goes away so the blower can't run on high at the same time the defogger is on.
Obviously things differ from year-to-year. I do not wish to appear like idiot-of-the-day so I just ran (engine on) my 1974 on the MAX setting with medium fan. It throws around a lot of air, just as I predicted based on my Driver's/Shop Manuals. Interesting day on the Forum!! Thanks for your input.
On a more pleasant side the Wife and I got out this morning in the Corvette with the top down for ~90 minutes. Cloudy but very nice. The Corvette hummed. Did the points/condenser/dwell a few days ago and it shows. Some of you out there remember those?
It's our 3xth Anniversary. Great way to share moments as she has put up with my Corvette good and bad moods for so long.
Last edited by Paul L; 05-22-2011 at 09:09 PM.
05-23-2011, 02:51 AM
#24
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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
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
05-23-2011, 02:54 AM
#25
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In some years going to MAX will engage the high blow relay no matter where the blower speed switch is, I don't think your 74 operates that way. MAX is as you say just a vacuum control , and just closes the door to the outside.
In some years the black wire ground we have talking about is switchable, in other words the ground is applied or taken away as a secondary control to turn the relay on or off.
The one I can remember is 78 , if the rear window defogger is on the black wire ground goes away so the blower can't run on high at the same time the defogger is on.
In some years the black wire ground we have talking about is switchable, in other words the ground is applied or taken away as a secondary control to turn the relay on or off.
The one I can remember is 78 , if the rear window defogger is on the black wire ground goes away so the blower can't run on high at the same time the defogger is on.
There's a thick purple wire that goes down the floorboard on the drivers side that connects to the rear window defroster. Sometimes you have to ground this wire out to get high speed on your blower.
05-25-2011, 05:47 PM
#26
Team Owner
Sometimes you just want to break and down and cry when working on these old cars. I have settled for a beer....
The new relay (pic) came in today (OK not Delco but...only $25.00) and I installed it. With great anticipation I turned the key to ON and the fan to HI and waited for the blast of high-speed air. Nope, nada, nothing, kaput, calm, extreme silence.
But everything seemed to check out? The 30-amp fuse was fine etc. No smoke was rising. The first three speeds still worked. I was now convinced the console switch was defective and did not look forward to pulling things apart.
Following Roger's lead of diagnosis rather than panic I cooled down and re-checked the GM wiring diagram. There right in front of me was the problem although it was not obvious! You never anticipate what has gone on over the years of ownership. The three-terminal connector going on the relay has orange, dark blue, and purple wires as mentioned above. The dark blue and purple wires were reversed!!!! I changed their positions and voila we have HI-speed air.
Nice to get this darn thing resolved. And it does not hurt to have re-wired the driver's side with a new 30-amp fuse receptacle and new 10- and 12-gauge wire etc along the way. That was needed as well. For those of us who are technically challenged these little victories are important.
Some Chardonnay and t-bones tonight to celebrate.
The new relay (pic) came in today (OK not Delco but...only $25.00) and I installed it. With great anticipation I turned the key to ON and the fan to HI and waited for the blast of high-speed air. Nope, nada, nothing, kaput, calm, extreme silence.
But everything seemed to check out? The 30-amp fuse was fine etc. No smoke was rising. The first three speeds still worked. I was now convinced the console switch was defective and did not look forward to pulling things apart.
Following Roger's lead of diagnosis rather than panic I cooled down and re-checked the GM wiring diagram. There right in front of me was the problem although it was not obvious! You never anticipate what has gone on over the years of ownership. The three-terminal connector going on the relay has orange, dark blue, and purple wires as mentioned above. The dark blue and purple wires were reversed!!!! I changed their positions and voila we have HI-speed air.
Nice to get this darn thing resolved. And it does not hurt to have re-wired the driver's side with a new 30-amp fuse receptacle and new 10- and 12-gauge wire etc along the way. That was needed as well. For those of us who are technically challenged these little victories are important.
Some Chardonnay and t-bones tonight to celebrate.
05-25-2011, 08:29 PM
#27
Race Director
05-25-2011, 08:53 PM
#28
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St. Jude Donor '12
Paul 74 when you place your A/C on max, your fan does not automatically go to high? I assumed they all did this. Maybe some years were different. Glad to hear you got everything fixed. With these old cars you never know what the PO did to anything.
05-25-2011, 09:15 PM
#29
Team Owner
Yes, and of course the irony is now that it is there and working I will never use HI fan with a convertible; either A/C or heat. It was just one of those "doesn't work" irritants that drives me crazy. I can't find another one this evening but come tomorrow!
05-25-2011, 09:32 PM
#30
Team Owner
"MAX - the system utilizes vehicle inside air only."
That implies only that outside vents are closed at whatever fan speed.
I had HI fan speed on "heater" this evening and it sure does blow heat.
As to year differences, just a comment. On the later C3s the fan is never off. On a 1974 the fan can be shut off by putting the fan in the "OFF" position and pushing the left wheel to the top "OFF" position. That shuts down the fan completely. If you leave that wheel in any other position (despite fan off position) it will groan on at low speed just like later C3s.
But as I said to Roger this was a little irritant project that just blossomed into too much of a nuisance, but thankfully resolved. I have the top down now and will just drive with the fan off.
07-06-2011, 05:53 PM
#32
What a great thread this was!! Last night while driving my 1976, my high speed motor started kicking on and off, then finally off for good. My lower speeds were all functional, but High did not come on at all. I read up the forum last night, and went to task this morning. All wiring seemed good, no shorts or opens. I found the fuse on the passenger side - coming from behind the distributor (Red wire), into the fuse, and then out as an Orange wire to the relay. When going from med to high, I heard a loud "tink" sound in the metal relay on the firewall. After a couple of trips to a couple of dealerships, I found a replacement relay at NAPA. Replaced it and no dice. I then started looking at the wiring again and when I moved the wiring I heard the high fan kick on then off. I pulled the wiring again and this time a saw a spark inside the fuse holder assembly followed by the fan turning on. When I was able to reproduce this continuously I visited my local Advanced Auto and purchased another fuse assembly and heat shrink. Some cutting, soldering, and shrinking, and the High fan is running continuously again - thanks all for the helpful information!!
10-05-2011, 03:51 PM
#33
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This thread helped me resolve the blower issue on my 68. Blower was running fine on low and medium speeds, but high speed was exactly the same force as low speed. A new blower relay solved the problem. And now that I have rebuilt the thumb wheel control unit with a kit, all is especially well!
Thanks for all the detailed tips!!
Thanks for all the detailed tips!!
