| Dash AC Fan speeds [message #80468] |
Tue, 13 April 2010 12:08  |
Jon payne
Messages: 495
Registered: May 2008
Karma: 1
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I thought I start a new thread regarding Dash Air. The last few posts on "Dash Air Rebuild" mentioned about the fan speeds and how to modify the wiring in order to turn off the fan when the switch is set to LO.
This reminded me about the fan speed control on mine. When the fan speed switch is set to LO, the fan speed is low (imagine that!). Then I move it up to the next position and what do you know the speed increases. Then up to the third position the speed decreases to the same speed as LO. Then moving to the forth position, HI, the fan stops. If I "wiggle" the switch I can hear a relay chatter and the fan will come on and off. So it seems that I have a dirty or defective switch on the control panel? Has anyone experienced this before?
And what could be causing the fan speed to decrease from the second position to the third? Could it be the resistor assy on the side of the HVAC box? If so anyone have the PN and where this part can be had?
Jon
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: Dash AC Fan speeds [message #80476 is a reply to message #80468] |
Tue, 13 April 2010 13:44  |
Jon payne
Messages: 495
Registered: May 2008
Karma: 1
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I'm the same way Dan! Got to have everything in working order! Stuff like this will drive me nuts until I get it fixed.
Jon
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: [GMCnet] Dash AC Fan speeds [message #80483 is a reply to message #80468] |
Tue, 13 April 2010 16:13 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Jon,
IIRC the fan only runs in the HI position if the alternator is producing
current.
Regards,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Jon Payne
Sent: Wednesday, 14 April 2010 3:09 AM
To: gmclist@temp.gmcnet.org
Subject: [GMCnet] Dash AC Fan speeds
I thought I start a new thread regarding Dash Air. The last few posts on
"Dash Air Rebuild" mentioned about the fan speeds and how to modify the
wiring in order to turn off the fan when the switch is set to LO.
This reminded me about the fan speed control on mine. When the fan speed
switch is set to LO, the fan speed is low (imagine that!). Then I move it up
to the next position and what do you know the speed increases. Then up to
the third position the speed decreases to the same speed as LO. Then moving
to the forth position, HI, the fan stops. If I "wiggle" the switch I can
hear a relay chatter and the fan will come on and off. So it seems that I
have a dirty or defective switch on the control panel? Has anyone
experienced this before?
And what could be causing the fan speed to decrease from the second position
to the third? Could it be the resistor assy on the side of the HVAC box? If
so anyone have the PN and where this part can be had?
Jon
--
Jon Payne/
76 Palm Beach/
Westfield,IN
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: Dash AC Fan speeds [message #80495 is a reply to message #80468] |
Tue, 13 April 2010 20:14 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Jon
It sounds like you are on the right track. The switch is probably the problem as you can get the high speed relay to come on intermittently by wiggling the switch. High speed position does connect the blower motor to the alternator thru the relay. The rest of the positions just connect the motor thru different value resistors to change the motor speed. You might get by by squirting some contact cleaner in the area of the switch contacts. I had a problem with my switch last year. I went to the junk yard looking for a replacement. I couldn't find any on the cars as there weren't any 70's GM cars there but I found that late 70's GM pickups and maybe vans had a switch that would work well the only difference was they don't have the removable knob but they do look good with their chrome knob. I didn't try Napa or Auto zone as I wasn't sure what would work and I needed an excuse to poke around the PICK a Part.
Roy
Roy Keen
Minden,NV
76 X Glenbrook
[Updated on: Tue, 13 April 2010 20:15] Report message to a moderator |
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| Re: Dash AC Fan speeds [message #80503 is a reply to message #80468] |
Tue, 13 April 2010 22:12 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Usually the problem is at the other end, at the resistor pack or the high blower relay as these are more exposed to the environment. Also in HI this is where the current is carried not in the switch. I forget if 76 has the "third relay" the delay relay which might have started in 77?? I would remove all the connectors at that end and spray them with Deoxit D5 anyway as they like to build resistance there and melt down on GM cars. However, the wiggle test seems to point to the dash switch in addiion to the bad connection at the HI blowere relay if you have to wiggle it to get the relay to click, but then it still doesn't go to HI. Sounds like 2 wrongs aren't making a right in this case. That's my armchair diagnosis.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Dash AC Fan speeds [message #80531 is a reply to message #80528] |
Wed, 14 April 2010 09:24 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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On Apr 14, 2010, at 8:15 AM, Michael Bozardt wrote:
>
>
> Jim Kanomata carries the correct switch. I replaced mine and added
> a new, not rebuilt, blower as my blower motor was noisy at start up.
> New AC Delco motor and squirrel cage $90.
> Still, the new motor(on a 74 GMC) is not working on high speed. My
> A/C guy has given me a check list and I hope to start using it
> today. I will post it if it works.
> The high speed is the only one directly connected to the battery
> through the alternator. I have not checked the wiring diagram to see
> whether it goes through the relay as well....Michael
> GEMRECS
Hi Michael
Yes, it does go through the relay.
Here is something that I posted in the past. Ignore the info about
the delay relay as it was only on the 77 and 78 models.
>
>
> The delay relay is the smaller relay at the very top of the panel.
> It has two leads - on mine they are brown and yellow and one has a
> male and the other a female terminal at the end of the leads. The
> leads are approx. 6 to 8 inches long. The female one connects to
> the male terminal on the lead to the blower motor. The male one
> leads to the short lead (purple on mine) that goes to the blower
> relay (terminal 1). If the delay relay burns out you can plug the
> male motor lead directly into the short female lead going to
> terminal 1 on the blower relay.
>
> The blower relay (below the delay relay but above the horn relay)
> has 5 terminals. When the blower relay is mounted with the 5
> terminals down, there are two on the left, one in the middle and two
> on the right.
>
> On the back left side it is #3 which has a red/white wire that leads
> to a fusible link and that goes into the harness and connects to the
> red wire from the alternator to the center stud of the battery
> isolater.
>
> On the front left is terminal #2. Mine has a dark blue wire that
> leads to the resistor package in the right side of the heater box.
>
> In the center is terminal #1. Mine has a short purple wire with a
> female connector. The male lead from the delay relay plugs into
> this (on mine right now I have the blower motor plugged into this
> as my delay relay is bad and disconnected).
>
> On the right rear is terminal #5. This has a short black lead that
> goes to a ground screw.
>
> On the right front is terminal #4. This has an orange wire that
> leads to the heater controls on the dash.
>
> Terminals 4 & 5 control the coil in the blower relay.
>
> Terminals 1 & 2 are normally closed and operate the blower when in
> low or medium speeds.
>
> Terminal 1 & 3 are normally open but when the dash switch is put
> in "high" or "max" it actuates the coil and the relay connects these
> terminals which give power to the blower directly from the
> alternator in order to get higher voltage and higher blower speed.
> At the same time it disconnects terminal 2 from the circuit.
Note that some relays had only 4 terminals. On these the ground is
done through the case to the mounting screw.
Here are some parts numbers that will work.
GMC 78Z Parts Book, 5 prong 1115858
NAPA, 5 prong 20 amp contacts - different bracket AR126
NAPA (see #72, page 3) 12 amp contacts, 5 prong AR109
NAPA 4 prong, grounded through case AR102
Echlin 12 amp contacts, 5 prong AR109
Everco 5 prong 2411
Four Seasons 5 prong 35767
AC/Delco 5 prong 15-8169
AC/Delco 4 prong, grounded through case 15-8172
The original relay had 12 amps contacts. If you should decide to use
the 20 amp contacts you would have to drill different mounting screw
holes.
Emery Stora
77 Kingsley
Santa Fe, NM
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| Re: Dash AC Fan speeds [message #80574 is a reply to message #80468] |
Wed, 14 April 2010 20:10 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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I believe the delay relay on the last 2 years was to allow the vac dampers to get to the position you had sellected in MAX AC before the fan went to HI. Otherwise the airflow was 'so great' the doors might not fully actuate and overcome the air flow. There is still the HI blower relay in addition the the delay relay and the resistor network.
John Lebetski
Woodstock, IL
77 Eleganza II
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