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About a year ago, I had extensive work done on my '75 280's heater. The problem, at the time, was related to antifreeze appearing on the passenger side floorboard. That problem was corrected. Since then, I've had a continuing intermitent problem with the front panel controls. 50% of the time, whenever you select defrost or any other control setting, the air arrives at the correct outlet and at the selected temp. The other 50% of the time, and this can be the first time you activate the controls or just an abrupt change while it is operating perfectly fine, it just blows cold air out the front vents that are for the AC only. I've since had the car to a radiator/AC/heater specialist and they traced all the vaccum hoses to be sure all are connected. So, unless there is a hidden problem with vaccum hoses, that is not the problem. I've had the problem looked at by two different repair shops, and none has been able to keep it working 100% of the time. Anyone else had same problem? Any suggestions would be appreciated. Thanks.
 

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speedex,

I think someone has over looked the basics. The heater doors are operated by a vacuum switch on the passenger front fender. The usual problem is the vacuum hose going to these switches,the switchs or binding of the heater door. In addition, the cable wire attached to the control lever on the dash control can bind and not open/close the door through the full range. This cable is very easy to bend. There are also unique clips which hold these cables in place and if one is left off the cable and housing will move together and not open the door through its designed range. What you need is a factory service manual which shows the operation of each function of the heater control system, which is also co-mingled with the air conditioning system!!
 

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I eliminated the A/C in my car and also pulled the magnetic vacuum valves too. I ran the vacuum straight from the manifold to the heater control manifold inside the car. It works great. I had a magnetic valve that leaked and a discharged A/C system.

Just some more useless, info. Take what you want.

:)

Aren
77 280z Mod.
Bend Area Datsun Association
www.bendareadatsuns.com
 

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hey aren77z

You bypassed the vacuum canister also? doesnt the engine produce less vacuum at certain speeds (hence the vacuum canister)? my cars heat works occasionally, and I can hear it when it quits, the vacuum to the control valve that operates the door on the drivers side seems to quit! I can hear it close back up and then it starts blowing cold out the middle. does that mean that my Vac canister might be bad and bypassing it altogether may help?
 
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