HVAC control panel compatibility

I installed a non AC HVAC control panel into my '89 that was originally equiped with AC. I did this because I converted the AC pump for OBA. I hate have controls for something my vehicle doesn't have. My problem is that my blend door doesn't seem to be working. Do you think the problem is related to the non HVAC control panel? Donor came out of a '87 or '88.

Symptoms:
On all settings it's the same I have a little bit of air coming out of the defrost vents, none coming out of the dash vents, except for MAYBE a little on the ones on the far ends of the dash, and none coming out of the vents for the rear seat.

History:
The previous owner installed a new heater core, and removed the AC evaporator before I bought it. I stripped out the entire interior, including the dash, and installed a much nicer doner interior right after I bought it. So I know all the heating ducts are connected.

Now mind you I did this right after I bought the jeep, so I don't know if it ever worked properly. I did test the heater fan but never tried to adjust the blend door on the test drive.

I know the easy thing would be is to install the original one and try it but it's been in the low 20s with freezing fog for the last week and half, I just moved to a new place with no garage too, and not to mention the original one is an hour away at my dad's unheated equally cold shop.

anyone???

I am not familiar with the heater box on your 89, so I am just speculating.

The blend door controls the mix of hot and cold air. There are also other doors that control the position the air is coming out of. From your description it seems like its the other doors that aren't working. IIRC those are controlled by vacuum. I would verify that you have vacuum to the interior and control panel.

I believe the older models have vacuum lines that connect to the controls behind the dash and if they are leaking then the entire HVAC defaults to the defroster. The little vents at the corners of the dash are also defroster vents to help defog the front two windows so if the HVAC system defaults to the defroster then you will still get air blowing out of the little defroster vents on the corner of the dash. Check your vacuum lines since it seems you have a leak and I would say you should start with the lines at the controls if it started this after you changed out the controls.

The AC/heater control in the dash is vacumn control, one line comming in and several lines going out to different controls/actuators under the dash on the driver's side close to the center hump. In my opinion, it is a terrible design but it seem to work ok for a while. The problem I see is the fact that some of the vacumn actuators under there have two vacumn lines to move them (the doors) to different positions and hold them there thus when there is no vacumn the default to the defrost position. In addition, the dash control is notorious for leaking when age set in and / or the hoses going to the actuator rotting and leaking.

If you have vacumn verified by pulling the dash and checking the controler assuming you have verified all the hoses are connected in the engine room the next step will be to look for leaks on/in the controler itself and work your way down to the actuators. Some years ago I had a problem with the dash mounted controler. My back door fix was to remove one of the hoses on an actuator and plugging it. I loose one position setting but otherwise every thing work fine. That was in 2007 so I do not remember exatly what I did and I do not have the shop manual with me to trace the (Spaghetti like) vacumn hoses.

I'll echo the vacuum comments. The only electrical function in the panel is the blower speed knob. The directional functions are all controlled by vacuum, if you have a vacuum leak you will only get air from the defrost vents as that is the "at rest" position of the blend door. The common culprit is a broken line going to the vacuum reservoir behind the passenger side of the front bumper, particularly where it goes behind the battery and down to the reservoir itself.

Talyn said:

The blend door controls the mix of hot and cold air. There are also other doors that control the position the air is coming out of. From your description it seems like its the other doors that aren't working.

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Yea I meant the other doors not the blend doors... My bad

Thanks for the advice everyone. I knew that some of the doors operated via vacuum but wasn't sure which ones. Thanks for clearing it up. I'm thinking I'll wait till it warns a little before I get involved in this project sounds like our could be a pain

I'm thinking that an originally air conditioned vehicle needs the proper control, if only to direct the ductwork's doors to open and close. Certainly you may have a vacuum leak, and the system will default to the defroster vent. But, when the system's top slider is in the off position, and the blower is not in its lowest speed, is there any air flowing from anywhere as you drive? The temperature blend door should be hooked to a cable attached to the lower slider, so no vacuum or electrical power. But, has the coolant bypass been removed, ans if so, has its vacuum line been disconnected or otherwise been plugged properly? It may be a source of vacuum loss, defaulting the system to defrost.

That was my first thought on the controls too.

Not sure about the coolant bypass. But will look into it. Do you know where it's located?

Since my original HVAC control panel is an hour away I'll check to see if I have vacuum, if I do then I'll wait to get the original controls to see if they work.

So is the air cold or hot that is coming out of the defrost vent

The bypass is right where the hoses go to the heater core, just on the outside of the firewall, on the right side of the engine compartment. It allows the coolant to turn around, and not enter the core when the temp slider is all the way to cold, to the left. With the wrong control, it may be causing a leak, if in fact it is still in the loop, and not being fed the proper vacuum signal.

1985xjlaredo said:

So is the air cold or hot that is coming out of the defrost vent

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Temp control works fine, just can't redirect air flow.

heyhar said:

The bypass is right where the hoses go to the heater core, just on the outside of the firewall, on the right side of the engine compartment. It allows the coolant to turn around, and not enter the core when the temp slider is all the way to cold, to the left. With the wrong control, it may be causing a leak, if in fact it is still in the loop, and not being fed the proper vacuum signal.

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Great! I'll take a look tomorrow when I put in the new battery. I recall seeing some capped vacuum lines in that general area, but never took notice as to if there was a valve in that area or not.