Home » Public Forums » GMCnet » Jeep TJ A/C Control Head
| Re: Jeep TJ A/C Control Head [message #366475 is a reply to message #366165] |
Sat, 04 September 2021 12:54   |
Greg C.
Messages: 224
Registered: October 2019
Location: Knoxville, TN
Karma: 0
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I think the biggest obstacle to overcome for everyone interested in this mod is going to be the ability to disassemble the passenger side factory dash without destroying it. Mine started breaking the moment I tried, and so it came out in about two minutes. In too many pieces to even contemplate salvage. So I am building an all new dash, driver and passenger side, that will allow easy opening and access to everything.
But once the dash is out, all the mods are relatively easy. Not technically difficult, merely time consuming.
The Jeep system is a defrost default system, meaning a loss of vacuum shifts the system to defrost mode, because the defrost flap is open all the time until vacuum closes it. My 77 GMC is a dash air default, with the defrost flap held shut by a spring until vacuum opens it. I had to reverse the action of the defrost actuator to close it upon vacuum signal, instead of opening it.
I've been told by someone on the forum ( I need to look up who) that there are vacuum solenoids that can use a vacuum signal on one port to apply vacuum on another port. If this is the case, then one of these could be used to pull open the defrost flap on the GMC when the Jeep control calls for defrost. In that mode, the Jeep control has NO VACUUM applied to the defrost actuator, because on the Jeep, its normally open with no vacuum applied. So you would need a solenoid that activates with a lack of vacuum at the sensing port and applies vacuum at the operating port, which would open the GMC defrost flap.
If one of these solenoids is available, then the defrost actuator on the GMC would not have to be modified.
This still leaves the modification of the dash air flap, which is held open by a spring/pivot wire. This is what makes it dash air default. You have to remove that spring and replace it with a 1/4" rod, and then move the actuator 5/8" to the other side of the 1/4" pivot rod, which reverses the action of the dash air flap, making it closed with no vacuum. You have to be able to get to the air box to do that, at least on a 77. I am not familiar with the earlier coach systems.
Again, I am more than happy to reply to any questions here on the forum, or a via phone, if someone has an interest and needs more information. I'm in the middle of the dash build, so until I get that done I won't have time to do a full write up. But I plan to.
Greg Crawford
KM4ZCR
Knoxville, TN
"Ruby Sue"
1977 Royale
Rear Bath
403 Engine
American Eagle Wheels
Early Version Alex Sirum Quad bags
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| [GMCnet] Re: Jeep TJ A/C Control Head [message #366480 is a reply to message #366475] |
Sat, 04 September 2021 20:52 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Greg,
I suspect the defrost/heat door is the same on all GMC's. This photo and
the following 4 show my replacement for that on my '76:
bit.ly/3jLSl8C
or
http://www.gmcmhphotos.com/photos/new-dash-panel/p24028-ducts-2c-deflector-doors-2c-and-actuators-installed.html
If I understand the problem correctly, one could move the spring from
forward of that door to the rear and replace the actuator-to-door rod with
a cable and pulley to the spring's shown connection.
Hopefully these photos will clarify the issue and perhaps help someone
else. I might even convert to the Jeep control myself. :-)
Ken H.
On Sat, Sep 4, 2021 at 1:54 PM Greg Crawford
wrote:
> I think the biggest obstacle to overcome for everyone interested in this
> mod is going to be the ability to disassemble the passenger side factory
> dash
> without destroying it. Mine started breaking the moment I tried, and so it
> came out in about two minutes. In too many pieces to even contemplate
> salvage. So I am building an all new dash, driver and passenger side, that
> will allow easy opening and access to everything.
>
> But once the dash is out, all the mods are relatively easy. Not
> technically difficult, merely time consuming.
>
> The Jeep system is a defrost default system, meaning a loss of vacuum
> shifts the system to defrost mode, because the defrost flap is open all the
> time
> until vacuum closes it. My 77 GMC is a dash air default, with the defrost
> flap held shut by a spring until vacuum opens it. I had to reverse the
> action of the defrost actuator to close it upon vacuum signal, instead of
> opening it.
>
> I've been told by someone on the forum ( I need to look up who) that there
> are vacuum solenoids that can use a vacuum signal on one port to apply
> vacuum on another port. If this is the case, then one of these could be
> used to pull open the defrost flap on the GMC when the Jeep control calls
> for
> defrost. In that mode, the Jeep control has NO VACUUM applied to the
> defrost actuator, because on the Jeep, its normally open with no vacuum
> applied.
> So you would need a solenoid that activates with a lack of vacuum at the
> sensing port and applies vacuum at the operating port, which would open the
> GMC defrost flap.
>
> If one of these solenoids is available, then the defrost actuator on the
> GMC would not have to be modified.
>
>
> This still leaves the modification of the dash air flap, which is held
> open by a spring/pivot wire. This is what makes it dash air default. You
> have
> to remove that spring and replace it with a 1/4" rod, and then move the
> actuator 5/8" to the other side of the 1/4" pivot rod, which reverses the
> action of the dash air flap, making it closed with no vacuum. You have to
> be able to get to the air box to do that, at least on a 77. I am not
> familiar with the earlier coach systems.
>
>
> Again, I am more than happy to reply to any questions here on the forum,
> or a via phone, if someone has an interest and needs more information. I'm
> in
> the middle of the dash build, so until I get that done I won't have time
> to do a full write up. But I plan to.
> --
> Greg Crawford
> KM4ZCR
> Knoxville, TN
>
> "Ruby Sue"
> 1977 Royale
> Rear Bath
> 403 Engine
> American Eagle Wheels
> Early Version Alex Sirum Quad bags
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: Jeep TJ A/C Control Head [message #366500 is a reply to message #366165] |
Sun, 05 September 2021 22:05 |
Greg C.
Messages: 224
Registered: October 2019
Location: Knoxville, TN
Karma: 0
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Senior Member |
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Ken, a cable would be a good idea. I used a new bicycle brake cable to run my windshield wiper control. My coach's factory wiper lever was gone, replaced by an aftermarket choke cable. I made new knobs on my lathe for headlight and wiper, and utilized a 1/2 x 20 bolt with a hole bored through it for the wiper control. By turning the knob counter clockwise, the cable is tightened and the wiper is actuated. I mounted a spring on the wiper motor control valve lever to deactivate the wiper once cable tension is removed.
I could have used the same bicycle cable, attached it to the vacuum motor and to the defrost lever, probably easier than how I did it. I welded a piece of 1/2 x 1/2 tube to the vacuum motor bracket and mounted a bell crank assembly on it which reversed the action of the vacuum motor. Again, not difficult, just time consuming.
Greg Crawford
KM4ZCR
Knoxville, TN
"Ruby Sue"
1977 Royale
Rear Bath
403 Engine
American Eagle Wheels
Early Version Alex Sirum Quad bags
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| [GMCnet] Re: Jeep TJ A/C Control Head [message #366502 is a reply to message #366500] |
Mon, 06 September 2021 06:32 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Windshield Wiper Control!!!? You mean you're still using that crazy
hydraulic wiper motor? After I've gone to the trouble of providing an
electric replacement for the past 15+ years? :-)
http://gmcwipersetc.com/ (even 'tho' son Alan still hasn't put it in his
name! :-(
Ken H.
On Sun, Sep 5, 2021 at 11:05 PM Greg Crawford
wrote:
> Ken, a cable would be a good idea. I used a new bicycle brake cable to run
> my windshield wiper control. My coach's factory wiper lever was gone,
> replaced by an aftermarket choke cable. I made new knobs on my lathe for
> headlight and wiper, and utilized a 1/2 x 20 bolt with a hole bored through
> it for the wiper control. By turning the knob counter clockwise, the cable
> is tightened and the wiper is actuated. I mounted a spring on the wiper
> motor control valve lever to deactivate the wiper once cable tension is
> removed.
>
> I could have used the same bicycle cable, attached it to the vacuum motor
> and to the defrost lever, probably easier than how I did it. I welded a
> piece of 1/2 x 1/2 tube to the vacuum motor bracket and mounted a bell
> crank assembly on it which reversed the action of the vacuum motor. Again,
> not
> difficult, just time consuming.
> --
> Greg Crawford
> KM4ZCR
> Knoxville, TN
>
> "Ruby Sue"
> 1977 Royale
> Rear Bath
> 403 Engine
> American Eagle Wheels
> Early Version Alex Sirum Quad bags
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: Jeep TJ A/C Control Head [message #366549 is a reply to message #366165] |
Tue, 07 September 2021 15:14 |
Greg C.
Messages: 224
Registered: October 2019
Location: Knoxville, TN
Karma: 0
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Senior Member |
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My wiper still works fine. It does not aggravate me to the point of moving it to the Spend Money list yet. Matter of fact, it's not on the repair list anymore since I replaced all the hoses and cleaned the filter.
If it starts being a pain, I'll do something about it. I also carry Rain X with me.
Greg Crawford
KM4ZCR
Knoxville, TN
"Ruby Sue"
1977 Royale
Rear Bath
403 Engine
American Eagle Wheels
Early Version Alex Sirum Quad bags
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