1984 Datsun 300zx


Old 01-31-10, 06:09 PM
Thread Starter
Join Date: Jan 2010
Location: ct
Posts: 9
1984 Datsun 300zx

Can any one out there tell me why my Datsuns heat blows
out of the vents when there is no heat or fan on? This
happens all the time. I do not know if it is the control buttons
or the "dampers" do not close. Has anyone experienced this
with their car? Thanks for your help!!
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Old 01-31-10, 07:31 PM
Join Date: Oct 2008
Posts: 1,312
If the cool/heat selector is on cool, then no heat should come out of the vents.

And if you have a selector for fresh/recirculate on fresh, then air will come out of the vents if the vehicle is moving (especially if a window is open). On recirculate no air should come out.

If the heat/cool selector is a mechanical type (goes to a cable and wire like the brakes on a bike), then might want to move that cable back and forth and see what it is moving under the dash...
Old 02-01-10, 09:05 AM
Thread Starter
Join Date: Jan 2010
Location: ct
Posts: 9
soozx hot air

Thanks Bill for your response. I do not know if the selector is
a mechanical type...I will check this out. Heat comes out of
the vents even when the selector is on cool or no heat. It
is so hot in the summer that it is difficult to drive around. No
matter what selection is chosen on the dash hot air is always
blowing. As you see I have had this car since 1984 so I am
familiar with what it never did before. I will check out your
suggection. Thanks again!
Old 02-02-10, 07:28 AM
Join Date: Dec 2009
Location: Kingsport, TN
Posts: 217
Does your car have a hot water shut off valve that probably is located near the firewall. It's purpose is to stop the coolant from entering the heat exchanger in the dash which is the source of the heat in the air flow. It could be sticking. Some are vacuum controlled - lines cracked and leaking preventing closure.

Does your car have a thermostat that controls the heat/flaps? Or is it completely manual? Reason why I ask is that I just went through a bout with my 1986 Porsche track car. It has an auto system and would blow full hot no matter what the setting. Turned out it was a faulty small blower motor tucked under the dash that sucks in cabin air past a thermister whose data is fed into the controlling software that mixes hot and cold air to regulate temperature. Turns out that in Germany, if a HVAC system fails, it must fail in full heat so that it protects occupants in cold weather. This is law in Germany, so I read.

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