Question regarding AC/Def/Heat

[Carolina Z]

Ok , all the vaccum lines appear to be connected as they should in the engine compartment. Went over all of them yesterday , made a repair or two as far as old lines that were getting hard due to age, a split in one at the connection, then checked as best I could under the control box for the AC / Heat/ Defroster etc, look as if they are all connected.

HERE is the problem , the damper will not close which does not allow heat into the car nor will the defroster work. The blower works fine , have cold air coming in the dash vents but no defroster or heat, there is no sound like the vaccum noise you here when switching from Bilevel or AC to heat or defrost..

Any ideas, this is a 77 280. One of the local Datsun / Nissan dealerships looked at me today like I was crazy when I ask if they had any ideas, oh they said I could leave it there and they would see if maybe one of the so called mechanics might have an idea...so obviously I left with my Z.

Anyone have any idea or ideas as to what is casuing this and how to fix the problem.

Thanks

Carolina Z

[Ray78Z]

I had a problem similar to that a few years ago in the 78. Fixed it (finally) by discovering under the dash, approx. above the ignition switch, there was a small bracket that holds a spring, which puts some pressure on one of the flap doors of the system. One of the screws was missing from the bracket, which then kept the spring from doing its job. I put a new screw in, and the spring pulled the door (open or closed..?) and the darn thing worked like it was supposed to. Hope it can be that simple for you....

Ray

[TomoHawk]

The flap for the defroster isn't controlled by vacuum. When you move the lever over to the end for the defroster, it moves a control cable that moves the flap for the defroster. There are some good diagrams in the FSM.

[First Gen Z]

On the heater/AC box under the dash there is a vacuum motor that controls the flap in the box. This device is on the left side of the heater/AC box and is clearly visible. It has two vacuum lines. It's proper name is "Mode door actuator". Check there first. Check the vacuum lines. Sometimes the actuator will stick do to age and a small nudge on the lever will break it loose. All of the vacuum lines should be replaced. The're old. I tried the 'cut the ends off ' trick and within days the ends would split again. A spool of that small hose is really cheap.

[Carolina Z]

Thanks guys for the suggestions, for one the spool of new hose is in the garage waiting for this weekend. As far as the other suggestions I will ck those out as well.

Does this model not have a vaccum canister up front , I have heard that it did and havent chekd it out yet, had the radiator replaced a month ago , prior to that this all worked, wondering if possibly the cannister is not connected as it should be , if in fact i do have one as I reattached it , but didnt ck the hose to it when doing so.

Anyway , will take these suggestions and see what happens, will let you know soon, thanks again for the info.

[Z Excellence]

under the hood on the passenger side is a white plastic bottle (vacuum tank) check the screws on the clamps that hold the 2 nipples that connect to the vacuum lines. Mine were loose and had the exact symptoms you are describing. Good luck.

[sblake01]

The flap for the defroster isn't controlled by vacuum. When you move the lever over to the end for the defroster, it moves a control cable that moves the flap for the defroster. There are some good diagrams in the FSM.

That's true but that has nothing to do with the flow of heat, only the direction of the air flow. I didn't answer eariler in this thread because my car has aftermarket air so it doesn't use the vacuum operated 'mode door' system. I am almost certain that his problem is vacuum oriented.

[ezzzzzzz]

You should pick up a Mighty Vac at the auto parts store. It can be used with a short piece of hose or the existing vacuum to test the dashpots (vacuum motors) for proper operation. The nice part is you can apply vacuum to individual components or the whole system to isolate problems. It isn't terribly complicated just a bother in those tight quarters under the dash. Like any other system, don't look at it s a whole but only individual parts that make the whole.

As to your specific problem...the MV can be used to test that vacuum motor for functionality. If it's good then just hand-over-hand back to the next component, then the next, until you've found the source of your problem. Don't assume anything is okay, especially those hoses in a 30 y.o. vehicle. You'll only know what is good or bad by checking everything that is applicable. It's only a matter of applying simple analytical troubleshooting.

[77 Z]

Z Excellence, ck your msgs..that was the entire problem, fixed it today , thanks for the information, I had changed the vac hoses but had not tightend the screws nor cked the fitting when doing so , did it and now it all works as it should.

77Z