'73-'74 A/C question

[69Crazy]

Can anyone tell me if the heater water shutoff valve was either deleted or not vacuum controlled in those particular years? Does anyone have a factory assembly manual or service manual covering those years. I have the manuals for my '69; but, I am trying to solve some confusion about the controls.

Thanks for the help,

Louie

 

[Tom73]

No heater shut off valve in 73/74. Why? who knows. maybe to save $2.00 per car.

For more info on the '73 Vette visit The '73 Spot at www.1973-corvette.com

tom...

 

[69Crazy]

Thanks

Thanks for the feedback. I thought that I might have a '73 vacuum assembly since there was no vacuum line through the firewall for the water valve. I will have to get the '69 hoses to finish my project. I don't think that any of the cars generated enough cooling to work well without the valve.

On the A/C optioned cars, what does the right side vent knob (on the console) do? On my '69 it opens the kick panel vent; but, that vent is used for fresh air intake (if I understand my assembly manual).


Thanks for the help,

Louie

P.S. Nice web page!

 

[Tom73]

Re: Thanks

On the A/C optioned cars, what does the right side vent knob (on the console) do? On my '69 it opens the kick panel vent; but, that vent is used for fresh air intake (if I understand my assembly manual).

On A/C cars that kick panel vent is tied into the HVAC box. It provides outside air to the system. Normaly open but when you turn the A/C control to MAX it closes and interior air is recirculated.

tom...

 

[69Crazy]

Vent knob

Is there a vent knob on the A/C optioned C-3's. If so, what vent is actuated.

Thanks
Louie

 

[Tom73]

If you are talking about those two vent knobs at the forward part of the console that control the foot air vents, no the A/C does not have those. Only "Vent" on A/C cars is the one on the HVAC control.

tom...

 

[69Crazy]

That clears things up

Those were the knobs that I was curious about. Thanks. I don't have any A/C optioned C-3's in our area, so I really appreciate the help.

Louie

 

[Steve's73]

Additional 73 A/C question

Can anyone explain the MAX A/C control? Specifically is there a difference in fan blower speed?

I have a 3 speed fan switch and all 3 speeds seem to work correctly, yet they as far as "air flow" out the vents NORM A/C and MAX A/C are the same. Not very strong at all.

I know there is a resistor on top of the evaporator for the fan speeds.

Can anyone confirm whether there is a resistor for the blower motor that may control a "Higher" rate of air flow?

Looking through my assembly manual and a hayes manual they both show an additional resistor for the blower other than the one on the top of the evaporator. Additionally Corvette Central sells a resistor that they call Hi/Low blower resistor.

Can anyone pinpoint the location of this resistor?

Thanks,

Steve

 

[Tom73]

Re: Additional 73 A/C question

Can anyone explain the MAX A/C control? Specifically is there a difference in fan blower speed?

I have a 3 speed fan switch and all 3 speeds seem to work correctly, yet they as far as "air flow" out the vents NORM A/C and MAX A/C are the same. Not very strong at all.

Steve,
Max has noting to do with the blower. The "MAX" setting just recirculates the air. It takes the cooled air from the passenger compartment and runs it back through the cooling. The normal or standard setting takes in outside air.

tom...

 

[69Crazy]

Look into obstruction

It also cuts off hot water valve in cars so equipped (your '73 has none) but you can add a valve from a late model GM truck....if interested, e-mail me for details and part numbers. The final step is to set the dampers to recirculate the interior air.

The resistor for most C-3's is located on the top of the A/C evaporator housing just on the engine side. When the fan is set on high you get a connection between 1 and 5 on the fan switch which sends power directly to the fan relay, bypassing the three resistors.

You can improve the air flow materially be eliminating the damper in the heater box that supposedly gives the option for bi-level air distribution. If you look at the plenum in the heater box, you will see that the damper (even in the full A/C position) cuts off 35 to 40 percent of the air flow. It might even have a greater negative effect due to turbulance it creates in the air stream. I would give up bi-level for the air flow.....especially now that the temperatures are soaring.

Just my $0.02 worth.....I have spent a lot of time lately staring at ducting, switching, wiring diagrams trying to create the new and improved C-3 A/C

 

[Steve's73]

Thanks for all the great suggestions. I will try and modify the damper for more air flow.

I've got the temperature at 40 with the POA valve and 134 just not enough air flow to keep up with the Florida sun.

69Crazy - I have a couple of questions.

Can you be more specific on your comment about the fan switch and the conections between 1 and 5?

Also, I would really like the details about the hot water cutoff, this sound like an excellent idea!

Do you have any opinion about some of the parts vendors that are selling a POA/VIR elimination kit for around $150.00 that I believe is supposed to convert the system into more modern orifice tube setup. Any thoughts?

Steve

 

[69Crazy]

Cool ideas

POA valve conversion is a good idea in theory. Whether the systems sold by ZIP, etc. work would have to be left to somebody who has tried. With 134a you need all the effeciency you can muster. That is why the system that 69MyWay and I are working on will use native 134a orifice tube components from a late model GM. I am building a modified A/C evaporator case to house the larger evaporator. If you are adament about staying with bone stock appearance, I would try the POA conversion kit.

The fan switch, in the high position, takes power from the system and routes it straight to the fan relay. This gives the fan full line voltage. If you choose any other fan speed, the current is routed through one of the three resistors that regulate fan voltage.

GMC part number 12380318 is a valve assembly that routes the water from the pump back to the engine or to the heater core. The advantage of this valve over C-3 stock is that you do not disrupt water flow from the pump when the valve is in the MAX postion. With part number 15706341 (the actuator) you have electrically controlled switching of the vacuum actuator that makes the valve assembly work. So, either a micro switch attached to your control head (or a simpler switch located somewhere under the dash) would give you control over the water flow. The C-3 systems do not need to compete with a heater core bringing the heater box up to engine temps when you don't need heat. In most parts of the country, there is enough warm air around to temper the output from the A/C evaporator when you need to warm the A/C settings. With water flowing through your heater box, that sucker gets hot. Yes, the air bypasses the heater core when the 1/16" damper is closed but the assembly (and the whole of your underdash area) is hot. Do you run your kitchen refrigerator connected up to your stove? Why Chevrolet decided that in '73 and '74 they would not have the heater core cutoff is beside me. If you want the dedicated connector for the actuator vacuum switch order part 12102747. The three parts will set you back around $90.00....they are fiercely proud of their parts in Detroit. Try www.parts.com for better pricing....I have found them to be about 35% cheaper than my local bandit....ahem, dealer.

Your best bang/buck ratio:
1. Heater core valve Difficulty level 1, very little head scratching on this one

2. Removal of bi-level damper. Difficulty level 2, more challenging as you have to dive into the dash area....aiiiieeeee!!!!, pull the heater box and then pull the damper from the box.

Or, you can just wait for our kit to be available and take care of both air flow and evap. effenciency in one effort. Technical term: monolithic biavaricide.

(killing two birds with one stone)

water valve pictured
Louie

 

[69Crazy]

Here is the bi-level damper. This view is from the A/C main outlet that leads to the selector/distributor duct. You can see that the damper cuts into nearly 50% of the plenum in the heater box. With the 45 degree bend that the air is forced to make, you don't get much coming through!

The heater box that I am constructing will be stock in appearance; but, the offending damper will be removed and the airflow will be otherwise improved with a general smoothing. Wow, porting and polishing my A/C system....cool!

 

[69Crazy]

Valve actuator

This is the actuator that uses electrical input from the control head (or a switch that you add) to control vacuum to the water valve in the heater hose. The top vacuum line goes to the intake manifold as a supply line. The lower hose goes to the water valve below.