AC / Heater Controls

[hoboos280z]

I'm the recent proud new owner of a beautiful '78 and last week my ac / heater controls stoped working. It seems to be set on panel ac and won't change to defrost. Before I start taking the dash apart does anyone know if this is a standard problem or are there any tricks to getting it back working. The interior is cherry (butterscotch really) so I don't want to do anything damaging, etc.

thansk,

Steve

[sblake01]

Not really what I'd call a standard problem but it does happen occaisionally. The top (AIR) lever of the control assembly is connected to a plastic cam type assembly that opens the defroster vents. If that plastic part breaks, you'll lose that part of the operation. Mine broke while it was on the defrost setting. It's easier to replace the entire assembly than to attempt to change that plastic part. I don't know where you'd find one. I bought mine from the junkyard. Beware that there are two types of heater control assemblies. One for cars with factory air and one for cars without. There are a few wires and cables that will have to be disconnected before the heater control will come out. Note where they all go if you decide to remove the unit.

[wal280z]

Do you have factory AC or is it a dealer / aftermarket add on?

If it is factory, then more than likely either your vacuum lines have deteriorated and can no longer move the mode door on the heater box OR the retaining clip on the vacuum actuator (for the mode door) has been removed or is missing and allowing the arm to displace off the mode door arm.

Take a look at my photo gallery - I took some pics of mine when it was out of the car and I refurbished the foam on it. For some reason the link won't work.

Download the FSM for the '77 at www.carfiche.com and review the AC section at the back of the book. The controls are nearly (if not) identical to the '78.

Be careful switching the vacuum hoses off the components if the vacuum lines are found to be faulty - the connections on them can be very fragile and break the nipple off. It's worth checking into those places before you tear into your dash.

Good luck.

Wayne

[EdMo]

I'm having the same problem and have started taking apart my interior some, mainly because I was replacing panel light bulbs and soon new sterio. After removing the middle console there are 4 vaccum hoses that plug into a small 4 nipple module. One of my hoses was not connected and I'm hoping that will do the trick .... but at this moment don't know for sure. The vaccum hoses also go up behind the fan (under glove box), where the Heater control valve is. I would say check the vaccum hoses first. FYI -Taking the middle console, glove box and fan are pretty simple, after that it gets kinda tight. Good-luck and if I find anything else this weekend I'll post if you haven't already fixed.

[sblake01]

My advice in post #2 was based on a non factory air system. With factory air the problem could be a simple as vaccum hoses and shouldn't require removal of the heater controls.

[hoboos280z]

Thanks for the feedback Stephen. Do you know how to tell if the car has factory air or dealer installed?

[hoboos280z]

Thanks Wayne. Do you know how to tell if it's factory air or dealer add on.

Steve

[Sailor Bob]

Mine is factory and the symtom you describe was caused on it by a small split in a vacum hose on the passenger side by the wheel well in the engine comp. I found three spots where the hoses slip onto connector sleeves (one was at the FI side) - hard to see but once removed to inspect it was evident. I simply cut off the bad spot and slid it back on - there was enough slack in the hoses that I could have done it two or three times. Otherwise $5 at Napa.

Now that is fine but can't adjust the heat. It's on or nothing - at least I have it if I want it.

[sblake01]

Thanks for the feedback Stephen. Do you know how to tell if the car has factory air or dealer installed?

Look at these two control panel attachments. Besides the difference in fan speeds note that on the 'AIR' lever that the first position on the non factory air is 'OFF' and the first position on the factory air is 'A/C'. The non factory system will also have a seperate compressor control knob that's not on the control panel.

[wal280z]

Thanks Wayne. Do you know how to tell if it's factory air or dealer add on. Steve

Stephen (Sblake01) posted a picture earlier in the thread that you should be able to positively identify the difference between factory or non-factory AC. Just in case a PO changed the faceplate of the control panel, the fan speed switch is the other obvious check as the switches cannot interchange between the two (I already tried).

The other difference noted is the vacuum lines coming into the passenger cabin. The vacuum line feeds the factory AC system and is not used any where else inside the cabin. Please note that there are still some cable controls (temperature and heater only setting) for the factory AC, but the rest of the functions utilize vacuum control.

[hoboos280z]

Thanks for the info. It's definately a factory air. The fan speed controls work but it only does ac and to the console. I love the ac but it's a little chilly having it on to keep the windshield from fogging up.

Does this still sound like a vacume line?

[sblake01]

It still could be a vacuum leak somewhere between the mode door actuator and and the vacuum selector valve, in hose D1 or D2. Do you have a Factory Service Manual? I don't want to get too technical if you don't follow what I'm saying. Section AC in the FSM has the descriptions, general service instructions, and trouble diagnoses and correction charts.