madkaw Posted May 30, 2009 Share Posted May 30, 2009 I noticed on my 81zxt that when I throttle up into boost and if I have my A/C on, the cold air will stop coming out of the center vents and hot air will start coming out on the floor. It's like the boost triggers a switch to change my A/C to Heat-what's up with that? Is it my compressor belt slipping( I checked it and it seems tight) or is ome kind of vacuum control not holding under boost situations? I'm not even sure where to start with this one. Quote Link to comment Share on other sites More sharing options...
johnc Posted May 30, 2009 Share Posted May 30, 2009 is ome kind of vacuum control not holding under boost situations? Most likely. Quote Link to comment Share on other sites More sharing options...
madkaw Posted May 30, 2009 Author Share Posted May 30, 2009 So I likely have a vacuum leak somewhere?! Quote Link to comment Share on other sites More sharing options...
johnc Posted May 30, 2009 Share Posted May 30, 2009 Maybe or some switch/sensor clicks off when boost reaches some level beyond what its designed for. The stock 280ZXT has about 7psi of boost right? Does your AC switch off at that point or at a higher boost psi? Quote Link to comment Share on other sites More sharing options...
slown280z Posted May 30, 2009 Share Posted May 30, 2009 I can't remember exactly but I'm pretty sure it's supposed to "turn off" at WOT to get the most power. I could be completely wrong about that though (but I know newer cars do this)... SO. What you could do is put a check valve on the vacuum line the does all of the controls coming out of the firewall near the heater core connections. This will work assuming it works right the rest of the time. Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 30, 2009 Share Posted May 30, 2009 Check for a leaking system reservoir check valve. If the system check valve leaks, when you go into boost the reservoir should have more than enough capacity to hold the doors in their positions even with some leaks. If it starts blowing hot air, that is a vacuum dashpot going away because you have no vacuum in the reservoir. And the most likely canidate is a leaiking check valve. The 83's have the little 'bullfrog' pump that will turn on and off to maintain vacuum in the HVAC system while under boost for sustained periods of time. If your system started blowing hot air, but out of the same vents (like Ford's do...) then it's a compressor cutout switch under boost. If your doors change position its because boost is blowing into your vacuum system due to either a leaking check valve or some really mazzive leaks in the tubing/switches that bleed out all vacuum in the reservoir tank almost immdeiately. But generally that would happen at partial throttle cruise without heading into boost, they would change state on lo vacuum situations as well, not just under boost...(with massive leaks, that is!) Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted May 30, 2009 Share Posted May 30, 2009 Put a one-way valve in your HVAC vacuum lines. The direction as follows: It should be able to blow into the intake manifold but not into the HVAC system. You DON'T want boost getting into your HVAC vacuum servos. They are not boost servos. Look at where my check valve is right below the vacuum brake booster line mount on the firewall. It's the little disc in the vacuum line..........................................here | Quote Link to comment Share on other sites More sharing options...
madkaw Posted May 30, 2009 Author Share Posted May 30, 2009 Sorry for the slow response, but I pulled another late nighter and worked when I should have been sleeping, so I layed down after posting. I loose my A/C just after I start reaching boost and the doors DO change from the vent to floor Tony. I don't doubt I have vacuum issues, and it sounded logical for what was happening. Cygnusx1, thanks for the visual, I will put a valve in place there when I replace all the rubber lines on this car-which will be soon. Tony, the leaking reservoir that you refered to is a resevoir for the HVAC specifically? I will look at the FSM after posting here. Quote Link to comment Share on other sites More sharing options...
madkaw Posted June 30, 2009 Author Share Posted June 30, 2009 I have been doing some serious searching and I must obviously have a vacuum problem. I put a my mighty vac on the vacuum tank and it didn't seem to hold vacuum well and the one way valve in the tank didn't seem to work. I had an extra tank and tested it and the one way valve worked. So my assumption is that the boost is pressurizing everything since the one way valve was not holding. I have installed the other tank , but now i am confused about the hose hook up. The FSM doesn't show any set -up like mine. I don't have a vacuum pump, but I do have an extra tank. I have 2 lines running from the firewall, but I have manual climate control. Please look at my pic and tell me what you think. My tank looks like the one in the FSM, but with the addition of the other tank Quote Link to comment Share on other sites More sharing options...
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