Strange Heating issue

[Zedyone_kenobi]

After finishing up my carb work I took her out for a drive and low and behold my next project surfaced. My car has previously been spot on with heater controls and A/C function. But now, I seem to have this strange problem on my 71 240Z with dealer installed AC (AC is irrelevant I think, but just to be sure I included it)

AIR

Off--------Vent--------Heat

------------------------

TEMP

Off---------------------Heat

------------------------

DEF

Def---------------------Room

As denoted by the location of the smilies, in this config, with the car fully warmed up, I get very warm air blowing through the defrost vents near the windshield. All is well. However, when I slide the smiley over to VENT as so:

AIR

Off--------Vent--------Heat

------------

TEMP

Off---------------------Heat

------------------------

DEF

Def---------------------Room

I get very cool air through the dash vents. You will note the DEF location is unchanged as I think sometime between now and last year, my DEF cable when south, so I have to assume since the defroster works like gangbusters that its stuck in the Def mode.

To see if the temp cable was working, I put it in this config:

AIR

Off--------Vent--------Heat

------------------------

TEMP

Off---------------------Heat

DEF

Def---------------------Room

And the air coming out of the defroster gradually cooled down, which I think is normal.

My question is why cant I get heat out of the vents?

I ordered a new set of cables and a new TEMP valve from MSA already so I have everything I need, although I am sure I will not need all of it. I am anxious for any answers.

ZED

Edited January 4, 2010 by Zedyone_kenobi

[260zCaliCar]

Just out of curiosity, when you set your config to "Air=Heat", "Temp=Heat" and "DEF=Room"

What do you get... Seems to me you should get nothing out of your defroster, nothing from your dash vents, and warm air coming out by your feet.

I just replaced my heater core/hoses/ducting/cables/controls about a month ago, so I know mine is working perfectly... But this was on a 74 260 so your 240 may direct air differently from mine

Edited January 4, 2010 by 260zCaliCar

[Darrel]

It's not like modern cars, when it says vent, it's exactly that a vent. It doesn't pass through the heater core.

[Arne]

Darrel is correct - the vents are vents, the heat only comes from the footwells (or the defrosters). After rebuilding a heater box or two, I can confirm that this is the way they were designed.

[Zedyone_kenobi]

Just out of curiosity, when you set your config to "Air=Heat", "Temp=Heat" and "DEF=Room"

What do you get... Seems to me you should get nothing out of your defroster, nothing from your dash vents, and warm air coming out by your feet.

I just replaced my heater core/hoses/ducting/cables/controls about a month ago, so I know mine is working perfectly... But this was on a 74 260 so your 240 may direct air differently from mine

Thats the thing.. I cannot move my slider to ROOM on the Def. The slider moves smooth like butter and binds on one end. So the cable is no longer functional, it is stuck on DEF and cannot go to ROOM.

So in order to get heat though the vents, I need to have all the sliders to the right, just like the FSM says. Which means my suspect broken cable on the DEF is the answer to my problem

Edited January 4, 2010 by Zedyone_kenobi

[zKars]

Zedy:

Listen to Arne and Darrel. You cannot get heat from the dash vents regardless of control settings. They only work when "Air" is in "Vent" and this connects you the outside. check page 13 of the supplemental chassis Manual of the FSM. I have a picture of it attached.

You're inability to move the slider to "ROOM" is a problem with the cable, the slider mechanism, or the connection of the cable to the flapper doors on the left side foot well heat outlets, which is what that control moves. It just closes the two external flap doors at the base of the unit which pushes all heat to the defrost vents when in the DEF position. I also attached a picture of the control cables on the left side from the 76 manual (very similar) for clarification.

You haven't somehow connected the defrost air ducts to the vent ducts have you? Or perhaps the central flapper valve in the heater box (under the #6) in the picture) is/was partly open allowing heated air to get into dash vent system.

I willing to bet you believe you once got hot air from these vents and are now convinced you can again. It should not work like that.

Hope this helps.

Jim

[Zedyone_kenobi]

It actually does. I think you may be right. My dash venting has not been messed with since the car was new, so I think what you said must be true...I will start to investigate when I get my new parts in.

[Zedyone_kenobi]

Those pics are Great, I downloaded the 72 FSM but do not have the chassis supplemental you mentioned. Looks like the AIR and DEF are on the left (drivers side), and the TEMP is on the right (pass side) close to the TEMP VALVE where the heater line comes in from the engine.

Seems the AIR cable is on the top in that second picture, and the DEF cable is on the bottom. Both look like I should be able to get to them. I think the DEF cable is the one I need to focus on. Those are a great help and that blow up of the ducting is INCREDIBLY helpful.

EDIT, just upon closer inspection, it would appear that the AIR lever in the dash actuates two different cables. One selects Heat or Vent locations for the central flapper, the other selects fresh or recirc air. Did I get this right. I am trying to make sense of the drawings. I am thinking the VENT selection gives you outside air, and the off selection gives you recirc.

Edited January 4, 2010 by Zedyone_kenobi

[zKars]

Excellent. A picture can really be worth a thousand posts....

Your description of what cable is connected to what seems accurate.

I have some control sets and HVAC units and cables that I can take pictures of so you can see the real and complete setup if need be, but I bet you have the information you need now to fix the problems.

If you find a missing or broken cable or clamp or screw etc, let us know.

Jim

[Zedyone_kenobi]

Will do, thanks ! This is going to be back breaking project me thinks.

[Walter Moore]

It's not that hard, if you are comfortable standing on your head...

[=Enigma=]

I had to visit my chiropractor for a few weeks after digging around under there to remove the A/C unit and route some new wiring for the taillight upgrade harness. Now I'm dreading putting it all back together and saving for another round of spinal manipulations and massages.