I'm guessing you got the aftermarket engine compartment conversion box ?. If so I have to think the resistor assembly has to go in the engine compartment and be in the direct air flow from the blower motor to keep it cool.

As far as wiring you might want to get a factory schematic and factory manual. I believe the switch you have a picture of is to make sure one of the internal flap doors are in a particular position before something else works. I could be way off on this but a manual should show this in a diagram.

I have a 74 service manual and there is a section on Heater and Air Conditioning and it shows the electrical wiring and also the vacuum door operation portions. You may have to get one for a 73 and sit down and trace things out.

I think the passenger kick panel flap as well as the one under the cowl is to control and get recirculated air or get fresh air. A person could change out the kick panels to a heat only style.

Jim

 

Heater Switches

Jim... thanks for the reply. Yes I have the aftermarket AC conversion box. I've seen the AC resistor mounted in these, but others have also said that one could also mount a heater resistor in the inside heater/ac box as long as its got air flow when the blower is on.

The switch pictured is on top of the interior heater/ac box (Diverter Door Switch?) and is triggered when the Heat/AC (center lever) is on Heat. My guess is it shunts something in the AC circuit.

Below is a 71-72 diagram. In this I can see the switch... but I'm still not sure what it "does" in the circuit.

Hope this helps,

I do have a complete 73 AC diagram on its way so I can confirm where everything goes. I'm just trying to figure out what stuff does as I don't want to reconnect stuff I don't need or leave out things that are required for heat.

Also I weighing my options on reconnecting the vacuum canisters but if they are needed for heat then I need to get them back in the mix.

Thanks!

 

Years ago I had the resistors out on some car I was donkeying with and turned on the circuit and I couldn't believe how much they glowed and heated up. I have to think they just need to be in an air flow to keep them from burning up. You do have to wonder why the factory chose the location they had VS where we might want to have them.

I didn't dive real far into the wiring diagram you posted but if I decided just to have heat, I would see what needs to be done as far as actuator doors needing to be moved between floor heat, dash heat, and defroster heat and then decide should I just keep a flap door in one position without the need for any vacuum source or do I need to keep some of the vacuum parts active. I've just never had to figure this out.

If I were to figure things out I might try turning on the ignition switch and get the blower to work at different speeds and then see if I can switch air flow between the floor, dash, and then the defroster vent and if things work without a vacuum signal. If things do work then I might bypass or remove all of the vacuum circuits. Who knows, things might work as you want. Sorry I don't have a more solid answer. If you do get things to work but later on find out during the summer you have hot air flow into the heater core, maybe put in a heater hose block off valve.

Jim

 

Hooking up the Heater in a Heat/AC delete 73 nova

Good point on the resistor location. I was also considering not using the AC relay but have decided to hook that up as well. The AC components are heavier than the heat-only components (core is bigger, fan is bigger, relay vs no relay, etc). So I'm going to replace everything with the AC components and... put them in the factory location under the hood.

It appears the default flapper door positions are "open". The vacuum closes the flappers. So it looks like I need to hook that back up as well. Otherwise I'll have nice cool air coming in the cabin at all times which kind of defeats the point of having the heater.

The rest of the parts are coming in this week so hopefully I'll be putting it back together in the next couple of weeks.

Correction: The cowl vent is default to Open, the kick panel is default to Closed.

 

I've got Heat and a Defroster in my 73 Nova!

Finished up the rejuvenation of my heater/defroster and learned a couple things along the way...

On my car all of the engine compartment parts were missing and the heater core was bad so I bought all the heater-only parts I needed and found they would not work. So if you have an original AC car and are buying parts, order the AC version of the parts.

Heater Core, Blower Motor, Relay (sends the actual power to the blower motor), Resistor (controls the current to the blower motor in the low/medium speeds) all need to be the AC versions.

Here's the 1973 Nova AC wiring diagram and I have outlined the part of the wiring that I eliminated for the heater-only setup.

Of note I re-connected the wiring to the Diverter Door switch but eliminated the tan wire that went to the Ambient switch. I've never gotten an answer on what that switch actually does... my guess is this would tell the AC system the heat was on. Any further insight on this switch is still appreciated.

Also I originally bought the fiberglass AC delete cover but found it would need to be modified to fit around my fender mount.

I bought the ABS AC delete panel. It fits between the heater core pipes so there were no fitment issues.

 

3rd Gen Nova Heater Reconnected

I ended up mounting the AC resistor inside the heater delete box and put the AC relay above it on the firewall.

On the interior I reconnected the vacuum actuator on the passenger kick panel and the vacuum actuator on the cowl. However, neither are functional because I have disconnected the vacuum line at the Heater Controls. I'm not sure yet where the other side goes, so I plugged it for now.

If I were to figure things out I might try turning on the ignition switch and get the blower to work at different speeds and then see if I can switch air flow between the floor, dash, and then the defroster vent and if things work without a vacuum signal. If things do work then I might bypass or remove all of the vacuum circuits.

Jim I followed your logic and I have muti-speed fan functions at the defroster, top of dash (AC vents) and at the floor so I'm satisfied the vacuum is only needed for the fresh air setting. Once I figure out where the other side of the vacuum control should go... I might reconnect it or I guess I could just get non-air kick panels.

The bottom line is though after 10 years I have a heater and defroster again.

 

my guess is this would tell the AC system the heat was on. Any further insight on this switch is still appreciated.

First off, congratulations on getting the heater to work to your satisfaction. That’s a win.

That’s pretty confusing. Based on the pin out on the first diagram it is the anti-dieseling relay but your component is clearly a switch.

The diverter door switch is tied to the blocking relay, the anti dieseling relay, the fan speed switch and the blower switch (why do you need two blower switches?) Ultimately this all ends up at the thermal switch under the hood which shuts off the compressor if you lose Freon.

So, this is my W.A.G. and theory of operation even though I can’t prove it from the diagram.

As I am sure you are aware, in defroster mode, the AC compressor runs to dehumidify the air before it is heated by the heater core. This produces dry warm air to defrost the windshield. In AC mode, there is likely an anti diesel solenoid on the carburetor that raises the idle speed to compensate for the load of the AC compressor. Therefore, in heater mode, that little switch of yours tells the engine you have the diverter door in the defroster position and thereby engaging the AC compressor as well as the anti diesel solenoid on the carburetor. Put the selector in floor mode and the switch opens, the compressor disengages and the engine returns to normal curb idle speed.

Steve

 

As I am sure you are aware, in defroster mode, the AC compressor runs to dehumidify the air before it is heated by the heater core.

I never knew that but it make sense.. since they have access to the AC compressor the engineers would use that to make the defroster more efficient. So although my defroster will not be as good as the factory AC setup... it will be at least as good as the factory heat-only setup.

Thanks for the insight!