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In my 87na Z, the A/C is coming out of my defrost vent when it is supposed to be coming out of the front vents. Also, under normal acceleration, the vents blow hot air. Any ideas? Thanks...............
 

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vacuum leak, guaranteed. Check your engine bay hoses and hope that it's an easy one to replace, otherwise you're going to have to take the dash apart to get to them.
 

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I had a similar problem with my 87NA and just before I took it to a mechanic, someone posted that sometimes the hoses on the vacuum canister (sits just behind the passenger side headlight) get crossed by someone who's unfamiliar with the z31. I switched them and suddenly my a/c worked fine and I've had no problems since. Just a thought.
 

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The black round reservoir-lookin' thing at the passenger front fender (in front of your collant reservoir) is a vacuum assist tank for your A/C. If the vacuum solenoid fails to control the A/C vacuum, the A/C will default to blowing hot air to your windshield. Sounds like you got the default mode working. Look at the 1/4" vacuum lines (three of them, a white hose, blue hose, and a red hose) one of them may be leaking. Check also the small vacuum line going from the rear of the vacuum manifold tree on the rear top of your engine. It goes to the hot water valve diaphragm. the line may be off, leaking, ot the valve is stuck open allowing hot water to compete with your A/C..
 

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If the vac hoses coming out the vac reservoir are the original colour-striped factory hoses then by now they will need replacement.

The white-stripe hose is the vac supply from the manifold. It may connect to a port labelled "M" on the vac tank. This port should also have a working one-way valve inside the reservoir, but it is inside so you can't see it. You should only be able to suck air through that port, not blow through it.

Blue-stripe hose is the switched vac from the electric valve on the reservoir to the water tap on the firewall.

Red-stripe hose is the feed to the HVAC controls inside the car. This may connect to a port labelled "F" on the vac reservoir.

A bit or sucking and blowing through a spare piece of vac hose should confirm the function of the ports on the reservoir.
Note that the water tap requires vacuum to shut off the water flow.
 
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