Temperature control slider

[Chickenman]

1976 280Z with Factory AC.

 

Anyone else have a 280Z with factory AC that can tell me if this is normal or not?

 

Temperature control lever does not have full range of motion. Stops well short of Full cold position and Full hot position. I've checked the cable that connects to the Thermostat control. Cable is free and not binding and Thermostat lever seems to be traveling it's full range.

 

I'm wondering if the extra travel is designed in for use on non-AC cars that use a manual style water temp valve, instead of the Vacuum controlled valve?

[Captain Obvious]

I can't help with your question about potentially different mechanical ranges of the heater valves between A/C and non-A/C cars, (so I probably shouldn't be in here at all) but in the spirit of the internet forum...

 

All of the temperature control valves are mechanically actuated with a cable. The vacuum operated valve that you have as part of your A/C system is in series with the temperature control valve and it's purpose is to completely shut off all water to the heater core the instant you put the control lever into any of the A/C positions.

 

Datsun is essentially saying "Nobody in their right minds would ever want to have warm air blowing on the windshield or floor while the A/C is on, so we'll just take that option out of the hands of the occupants. We'll just turn off all the water any time the A/C is on."

 

I disagree with that design decision, but I wasn't there when they made that call. 

[Zed Head]

I have a 76 with factory AC.  When I got it the temperature control cable (or rod, that's how I think of it since it's solid) was kinked from somebody forcing it in the past.  So it didn't move the full range.  The kink was behind the panel so you couldn't see it until the panel was removed.  After fixing that I'm pretty sure it moved the full range.  In other words, it seemed to work right.  But I've modified it since then.

 

My thermostatic control capillary was dead so the system went from no heat to full heat within about 1/8 of the lever's range.  I installed a Honda control valve (CO wrote a thread on it - thanks!) which works great except that it also only need  a small (tiny) amount of movement to flow lots of hot coolant.  Way more than needed.  Had to redrill some holes and fabricate some new actuators to get more fine control.

 

My AC cooling doesn't work either, the system needs maintenance.

 

Somebody needs to find a modern system that can be plumbed in to our cars, with heated conditioned air for the windshield and through the top vents, like today's cars do.  There's got to be something out there.

[Chickenman]

I'm beginning to think it's designed in. From what I can tell, the cable is running freely with no kinks. But it is a solid hard stop in the control mechanism itself.  I did have it apart earlier this year, so I wonder if I assembled something wrong in the control head.  Your comment on the short range of the Thermostatic control does raise questions though. I' guess I'm just gonna have to pull it all apart and examine things a bit more closely.

 

Heater blower is a bit noisy and needs some lubrication. Maybe a Winter or Fall project. I can live with the slight whine from the blower motor and I've got the AC working freezy cold right now.

 

FYI. Modifying the OEM system to give heated conditioned air to the defrosters like modern cars is very easy. Just add a jumper circuit in parallel to bypass the Thermostatic Control switch and the Micro switch on the Mode lever.  Circuit is already relayed, so a simple Push On - Push Off switch will work. There;'s a spare switch plate cover on the center console that can accept a switch. You can probably find some factory AC switch to fit. Button = Off and AC system works as Factory design. Button = On and system AC will work in all modes and temperatures. Easy Peasy.

 

Living in the PNW, I know how important heated air, that has been dried by the AC system is.

Edited June 22, 2015 by Chickenman

[Captain Obvious]

Actually the stock system makes it impossible to do what you want to do. You can never have heated, conditioned air to the defrosters. Ever.

 

Because of the design of the air flow system, the only location to ever exit conditioned air is from the "vent" locations. You can never have conditioned air come out of the defroster holes or the floor holes. Dash vents only.

 

So while it would be relatively easy to bypass the electrical  portion of the system and add provisions to make it possible to turn the compressor on regardless of the slider position, you simply cannot control the air exit position the way you really need it. And not only that, but when in the "DEF" or "HEAT" positions, the dash vents are completely closed off, so you'd freeze up your evaporator because you wouldn't have any airflow through it.

 

So the best you could do is modify the electrical portion to allow independent control of the compressor and then put the slider in the BI-LEVEL position. That way you could get heated air on your feet and some conditioned air out of the dash vents. That air would mix inside the passenger compartment through convection currents and the end result might defrost the windshield.

 

Might be better than stock, but certainly not as good as modern cars.

[Chickenman]

^ You are indeed correct. I forgot about the simplistic nature of the Factory AC routing only through the Vents. Bi-Level would give you the best mix of air currents with AC.

 

Bypassing the thermostatic control  should still be of benefit as the air drying effects of running the AC should lower the humidity levels in the cabin significantly. The small cabin area of the Z helps in that respect.

 

Edit: Actually, the factory system allows you to do that already.  The FSM on page AC-9 shows Bi-level selected with the Temp switch at about 40% with AC actuated. Heated air via Defroster ducts and Air Conditioned air flowing via center Vents is flowing through the system. Something is definitely wrong with my  slider control.

 

So the outcome of this, is that our discussion led me to the diagram in the FSM that shows that my Temp lever is not moving the full range. I believe it is a problem in the control lever system itself, as it is a " Hard " stop... not the typical soft or binding stop of a kinked control cable or a sticky control valve.

 

Time to rip things apart...again!!

Edited June 22, 2015 by Chickenman

[Chickenman]

Just a follow up on this. There is a design " Flaw " in the Temperature slider for factory AC with Auto AC cars. It looks like they use the same mechanism for both AC and -non-AC cars.

 

The Hot side turned out to be a cable clamp adjusted improperly. Once that was fixed the Temp slider goes all the way to the end of the Hot range. However, when turned to Cold, the slider hits a " Hard Stop " with the lever under the " T " of " Temp", leaving about 1/2" of range un-usable.

 

Turns out the  " Hard Stop " is the detent spring and ball holder for the temperature lever. It prevents the last 1/2" of travel... but that is the way it is designed. Just in case anyone else is having sleepless nights wondering about this...

 

While I was under there I pulled the complete Heater motor box to clean things. Heater motor had surprisingly little wear on the brushes and commutator. But there was a fair amount of copper dust from the brushes. I flushed everything with Brake Clean, lubricated the end cover bushing with Amsoil synthetic grease ( there was virtually no grease in the bushing ) and gave the other end a couple of drops of 3 in 1 oil. Motor should be much quieter now. Cleaned up the fan and vents and replaced some of the foam. Should be good for another 37 years. 

 

From the condition of the motor, I think the PO had replaced it with a new one sometime ago.

[Chickenman]

Serviced the Vacuum Selector switch also. New silicone grease as Sarah wrote up. Going to test all the Vacuum Diaphragms with my " Mighty Vac " next. I know the Heater floor vent one works. Sucky test...