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Late Model A/C control

GC
Greg Crawford
Tue, Jun 8, 2021 11:51 PM

SteveW was interested in what I was attempting to do with my HVAC controls, so here is a brief description.

My 77 Royale HVAC controls did not actuate the vacuum motors correctly, or the fan speeds. I piddled with the controls for a while and then just
decided to go a new route. I selected 1999-2004 Jeep Wrangler HVAC controls, because a cheap one could be had for proof of concept, and I am very
familiar with Jeep parts.

First thing is that the Jeep does not have a temperature control cable like the GMC. It uses a Blend Door Actuator, which is an electric drive motor
controlled by the temperature knob on the HVAC panel. This does not go through an on board ECM like many, or most, of the new controls do. It's three
wires, and it works great. I machined an adaptor on my lathe to fit in the BDA (Blend Door Actuator), and made an aluminum adaptor plate to mount the
BDA to the HVAC box. Fairly simple, just took a few minutes to do. This fits the BDA directly over the blend door lever on the coach, formerly
controlled by the push-pull cable from the GMC control panel. Now when you dial hot or cold on the Jeep panel, the BDA moves the coach blend door as
it should. First problem solved. BDA's are cheap, $22 or so.

Second problem. You may read that the coach defaults to defrost when it loses vacuum to the controls. Mine does not. I think most later model vehicles
do, but not my 77. The defrost door is held tightly shut by a spring. The Jeep door DOES default to open. When you select "Defrost" on the Jeep
control, it has ZERO vacuum to the actuator.  The Jeep defrost door is held shut by vacuum in all positions but defrost and defrost/heat. So there is
no vacuum available from the Jeep control to open the coach defrost door when you select "Defrost". My fix is this. I removed the spring holding the
defrost door shut, and I'm making a bell crank assembly that will reverse the action of the defrost actuator. So, like the Jeep, vacuum will pull the
defrost door shut in all positions except Defrost. At that point, a relocated spring will pull the door down, opening it and gaining defrost action.
Second problem solved.

Third problem is that the dash vent door on the GMC defaults to open on mine. It too is held open by a spring. I am removing the spring, moving the
vacuum motor rearward about 3/4 of an inch to get the actuator link on the back side of the dash vent door hinge rod. I have to make a new hinge rod,
as the other one is also the spring. By moving to the back side of the door hinge rod, this reverses the action of the door, so it will be Normally
Closed, and open with application of vacuum, per the Jeep control. Third problem solved.

Fourth problem is that the Jeep control is wider than the GMC control and the dash must be modified for it to fit. My dash pretty much imploded as I
was trying to remove it, so I will be fabricating an all new dash from scratch, similar but not exactly like Ken Henderson's great write up on his
dash.

I'm sure there will be more problems to overcome, but I don't think it is insurmountable. A cheap Jeep control is $48.00 on ebay, up to $178.00 from
Chrysler. I got a new BDA for $22, and one from a junkyard along with the wiring harness and vacuum harness out of a wrecked Wrangler for $10.

We'll see how it goes.

Greg Crawford
KM4ZCR
Knoxville, TN

"Ruby Sue"
1977 Royale
Rear Bath
403 Engine
American Eagle Wheels
Early Version Alex Sirum Quad bags

SteveW was interested in what I was attempting to do with my HVAC controls, so here is a brief description. My 77 Royale HVAC controls did not actuate the vacuum motors correctly, or the fan speeds. I piddled with the controls for a while and then just decided to go a new route. I selected 1999-2004 Jeep Wrangler HVAC controls, because a cheap one could be had for proof of concept, and I am very familiar with Jeep parts. First thing is that the Jeep does not have a temperature control cable like the GMC. It uses a Blend Door Actuator, which is an electric drive motor controlled by the temperature knob on the HVAC panel. This does not go through an on board ECM like many, or most, of the new controls do. It's three wires, and it works great. I machined an adaptor on my lathe to fit in the BDA (Blend Door Actuator), and made an aluminum adaptor plate to mount the BDA to the HVAC box. Fairly simple, just took a few minutes to do. This fits the BDA directly over the blend door lever on the coach, formerly controlled by the push-pull cable from the GMC control panel. Now when you dial hot or cold on the Jeep panel, the BDA moves the coach blend door as it should. First problem solved. BDA's are cheap, $22 or so. Second problem. You may read that the coach defaults to defrost when it loses vacuum to the controls. Mine does not. I think most later model vehicles do, but not my 77. The defrost door is held tightly shut by a spring. The Jeep door DOES default to open. When you select "Defrost" on the Jeep control, it has ZERO vacuum to the actuator. The Jeep defrost door is held shut by vacuum in all positions but defrost and defrost/heat. So there is no vacuum available from the Jeep control to open the coach defrost door when you select "Defrost". My fix is this. I removed the spring holding the defrost door shut, and I'm making a bell crank assembly that will reverse the action of the defrost actuator. So, like the Jeep, vacuum will pull the defrost door shut in all positions except Defrost. At that point, a relocated spring will pull the door down, opening it and gaining defrost action. Second problem solved. Third problem is that the dash vent door on the GMC defaults to open on mine. It too is held open by a spring. I am removing the spring, moving the vacuum motor rearward about 3/4 of an inch to get the actuator link on the back side of the dash vent door hinge rod. I have to make a new hinge rod, as the other one is also the spring. By moving to the back side of the door hinge rod, this reverses the action of the door, so it will be Normally Closed, and open with application of vacuum, per the Jeep control. Third problem solved. Fourth problem is that the Jeep control is wider than the GMC control and the dash must be modified for it to fit. My dash pretty much imploded as I was trying to remove it, so I will be fabricating an all new dash from scratch, similar but not exactly like Ken Henderson's great write up on his dash. I'm sure there will be more problems to overcome, but I don't think it is insurmountable. A cheap Jeep control is $48.00 on ebay, up to $178.00 from Chrysler. I got a new BDA for $22, and one from a junkyard along with the wiring harness and vacuum harness out of a wrecked Wrangler for $10. We'll see how it goes. -- Greg Crawford KM4ZCR Knoxville, TN "Ruby Sue" 1977 Royale Rear Bath 403 Engine American Eagle Wheels Early Version Alex Sirum Quad bags
SW
Steve Weinstock
Wed, Jun 9, 2021 2:48 PM

Thank you Greg !!

--
Steve W
1973 : 23'
Southern California

Thank you Greg !! -- Steve W 1973 : 23' Southern California
BV
Bill Van Vlack
Wed, Jun 9, 2021 4:31 PM

Greg,
Great work electrifying the blend door!  Photos and part numbers?

Perhaps a vacuum solenoid manifold, an arduino, and an electrical multi-position electrical selector switch would be a viable replacement for the
vacuum controls.

--
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid
November 2015.

Greg, Great work electrifying the blend door! Photos and part numbers? Perhaps a vacuum solenoid manifold, an arduino, and an electrical multi-position electrical selector switch would be a viable replacement for the vacuum controls. -- Bill Van Vlack '76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid November 2015.
TM
Tom McManus
Wed, Jun 9, 2021 4:52 PM

I played around with the AC on my 77Royal for 3 years. Between the vacuum controls not working most of the time and just dealing with 44 year old
components, I just went aftermarket. Electrically controlled damper and temperature. Wasn't that hard! Here is a link to my install.
http://www.gmcmhphotos.com/photos/g7355-hvac.html

Tom McManus
1977 Royale

Chesapeake VA

I played around with the AC on my 77Royal for 3 years. Between the vacuum controls not working most of the time and just dealing with 44 year old components, I just went aftermarket. Electrically controlled damper and temperature. Wasn't that hard! Here is a link to my install. http://www.gmcmhphotos.com/photos/g7355-hvac.html -- Tom McManus 1977 Royale Chesapeake VA
BV
Bill Van Vlack
Wed, Jun 9, 2021 5:16 PM

94nubble wrote on Wed, 09 June 2021 11:52

I played around with the AC on my 77Royal for 3 years. Between the vacuum controls not working most of the time and just dealing with 44 year old
components, I just went aftermarket. Electrically controlled damper and temperature. Wasn't that hard! Here is a link to my install.
http://www.gmcmhphotos.com/photos/g7355-hvac.html

Nice installation; I imagine there was a little custom work under the dash; did you have to remove the dash to connect?

BTU's/Tons?  Any outside air function?

Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid
November 2015.

94nubble wrote on Wed, 09 June 2021 11:52 > I played around with the AC on my 77Royal for 3 years. Between the vacuum controls not working most of the time and just dealing with 44 year old > components, I just went aftermarket. Electrically controlled damper and temperature. Wasn't that hard! Here is a link to my install. > http://www.gmcmhphotos.com/photos/g7355-hvac.html Nice installation; I imagine there was a little custom work under the dash; did you have to remove the dash to connect? BTU's/Tons? Any outside air function? -- Bill Van Vlack '76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid November 2015.
TM
Tom McManus
Wed, Jun 9, 2021 7:09 PM

Bill Van Vlack wrote on Wed, 09 June 2021 13:16

94nubble wrote on Wed, 09 June 2021 11:52

I played around with the AC on my 77Royal for 3 years. Between the vacuum controls not working most of the time and just dealing with 44 year
old components, I just went aftermarket. Electrically controlled damper and temperature. Wasn't that hard! Here is a link to my install.
http://www.gmcmhphotos.com/photos/g7355-hvac.html

Nice installation; I imagine there was a little custom work under the dash; did you have to remove the dash to connect?

BTU's/Tons?  Any outside air function?

No, I did not remove the dash and the only "Custom" thing I did was to connect the AC/heater vacuum pots together so they open and close opposite
each other. Simple rod between the damper arms. I dumped the air straight into the box that is below the dash. The 4 tubes feed into it.
http://www.gmcmhphotos.com/photos/g7332-1977-hvac.html No outside air, I just open the windows.

--
Tom McManus
1977 Royale

Chesapeake VA

Bill Van Vlack wrote on Wed, 09 June 2021 13:16 > 94nubble wrote on Wed, 09 June 2021 11:52 > > I played around with the AC on my 77Royal for 3 years. Between the vacuum controls not working most of the time and just dealing with 44 year > > old components, I just went aftermarket. Electrically controlled damper and temperature. Wasn't that hard! Here is a link to my install. > > http://www.gmcmhphotos.com/photos/g7355-hvac.html > > Nice installation; I imagine there was a little custom work under the dash; did you have to remove the dash to connect? > > BTU's/Tons? Any outside air function? No, I did not remove the dash and the only "Custom" thing I did was to connect the AC/heater vacuum pots together so they open and close opposite each other. Simple rod between the damper arms. I dumped the air straight into the box that is below the dash. The 4 tubes feed into it. http://www.gmcmhphotos.com/photos/g7332-1977-hvac.html No outside air, I just open the windows. -- Tom McManus 1977 Royale Chesapeake VA
GC
Greg Crawford
Thu, Jun 10, 2021 12:58 AM

I am taking pictures as I go. Once I get all the bugs out, I will post them all in the Photo Forum.

I don't have a part number handy for the BDA, but it fits a 2000 Jeep Wrangler. Same with the control panel. You can get them on ebay, Rock Auto,
Autozone, etc.

--
Greg Crawford
KM4ZCR
Knoxville, TN

"Ruby Sue"
1977 Royale
Rear Bath
403 Engine
American Eagle Wheels
Early Version Alex Sirum Quad bags

I am taking pictures as I go. Once I get all the bugs out, I will post them all in the Photo Forum. I don't have a part number handy for the BDA, but it fits a 2000 Jeep Wrangler. Same with the control panel. You can get them on ebay, Rock Auto, Autozone, etc. -- Greg Crawford KM4ZCR Knoxville, TN "Ruby Sue" 1977 Royale Rear Bath 403 Engine American Eagle Wheels Early Version Alex Sirum Quad bags