I have a clean 1987 300zx with 67k, at 2000+ rpms - the a/c shuts down and the vents blow out warm air. I have had mechanics look at it and they cannot figure it out. Please help.

Cooling radiator may need cleaning and the system may need topping up or new fluid entirely. Any work needs to be done by proper air technitians as it contains dangerous stuff.

Hi Chris, sounds like your thermostat may be worn and not closing all the way which would cause your engine to run cool at times. If you have a temp gage it should tell you if the engine is actually warming up or not. If not I would replace the thermostat.

As per your problem mentioned. There are few solved help links to troubleshoot these problems. Go through the list and Click the link below:----

2000 Toyota Avalon: No heat on Passenger Side?

http://whatisbyme.blogspot.in/2012/05/2000-toyota-avalon-no-heat-on-passenger.html

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No heat on Oldsmobile Silhouette?

http://technoanswers.blogspot.in/2012/02/no-heat-on-oldsmobile-silhouette.html

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Heater blows cold?

http://schematicsdiagram.blogspot.in/2012/02/heater-blows-cold.html

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Heat blows cold on drivers side and hot on passenger side?

http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html

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Hot air on the driver's side vents only?

http://repairhelpcenter.blogspot.com/2012/01/hot-air-on-drivers-side-vents-only.html

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Temperature gauge does not move and no heat when heater is ON?

http://technoanswers.blogspot.com/2012/01/temperature-gauge-does-not-move-and-no.html

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1992 Toyota Camry: A/C Control light Flashing and A/C not Blowing Cold?

http://technoanswers.blogspot.in/2012/04/1992-toyota-camry-ac-control-light.html

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No heat, blower blows only cold?

http://technoanswers.blogspot.in/2012/02/no-heatblower-blows-only-cold.html
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Ford F150 Ac only blows through defrost vents?

http://technoanswers.blogspot.com/2012/01/forf-f150-ac-only-blows-through-defrost.html

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Dodge A/C come out of defrost vents only?

http://technoanswers.blogspot.com/2012/01/dodge-ac-come-out-of-defrost-vents-only.html

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Ac vacuum line on dodge cummins?

http://technoanswers.blogspot.com/2012/01/ac-vacuum-line-on-dodge-cummins.html

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Ford ranger AC blows cold through defrost vents instead on cabin vents?

http://technoanswers.blogspot.com/2012/01/ford-ranger-ac-blows-cold-through.html

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2005 Chrysler PT Cruiser: A/C Blows Warm?

http://whoisbyme.blogspot.in/2012/06/2005-chrysler-p8t-cruiser-ac-blows-warm.html

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2009 Mercury Grand Marquis: A/C blows Cold From Defrost Vent Only?

http://whoisbyme.blogspot.in/2012/06/2009-mercury-grand-marquis-ac-blows.html

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AC not blowing through Vents on 2007 Chevy Trailblazer?

http://schematicsdiagram.blogspot.in/2012/04/ac-not-blowing-through-vents-on-2007.html

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Passenger side temperature is warm air out of dash vents?

http://schematicsdiagram.blogspot.in/2012/04/passenger-side-temperature-is-warm-air.html

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These will help.

Thanks.

What do you mean when you say it wont shut off? is it blowing hot air or do you just feel a lite flow of hot air even if you have the settings to cold?

If this is the problem that you always feel hot air at low flow and the ac goes to hot air then i would say one of two things, first if you have the selector to cold and you feel hot air then there may be a problem with the blend door, this door move to allow hot or cold air, the door may be broken or just a bad motor that controls it. keep in mind if the ac system shuts down for any reason the air then will be warm, it will be about the same temp as outside and maybe a little hotter.

this problem almost sounds like the ac compressor shuts off and then you are getting the outside air which is hot, there are many reasons for the compressor to shut off, it could be the compressor clutch heating up and disengaging , this would be due to a bad compressor clutch.

another reason is the fans are not working, the best thing to do is when the system starts to blow warm check and see if the compressor is running, start engine and look at the front of compressor, with ac off the front of it will not move, and then with ac on the front will spin, check it out and let me know, if it blows warm air and ac is not working then it may be compressor problem but if you are getting warm air and the compressor is spinning then it may be a door problem.

This is hard to check with out testing the system, so i listed a few things to check and let me know the out come. also the ac blows cold for how long before it gets hot air blowing out of the vents, good day.

I have a feeling that no one is checking the blend door in the plenum.

That is correct, the air blend door actuator. "flapper valve" may need to be replaced or cleaned and free from binding up. Good luck and hope this helps. If there is an Auto Zone in your area, they can order the part you need and give you the step by step instructions to removing the old actuator and replacing it if it's damaged. Good luck and keep me posted, be glad to help. 

you have a bad blend door or just stuck

if it isnt the iac probably the pcv valve positive crankcase vent. it is on a vacuum line somewere under hood. or check the air cleaner, the hose with the small filter underneath the air filter. i take its fuel injected?

Sounds like you have a plenum door that is not opening when you go into defrost mode. You will have to check all your vacuum hoses and switching valves under the dash to see which one is not working. Hope this helps.

I had same problem on 2000 Lesabre blowing cold on passenger and warm on driver. I fixed it by adding more freon even though it had 28 pounds of preasure. Now it works great!