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
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
