HB280ZT Posted June 6, 2004 Share Posted June 6, 2004 Hi All, Well I am having vacuum issues with my AC/heater controls and was wondering what others did to fix the problem. Car specs first: 77 280Z 82 280ZX turbo motor On the 280Z you have a dash pot that is connected to the D solenoid with standard vacuum to the S1 solenoid, then to the bottle and back to S2 solenoid. Well the ZX motor does not have the dash pot and it has no provision to add one. So how did you all that have ZXT motors in a Z get the AC/heater controls to work correctly? Oh yes I did check the lines and then are good! Thanks HB280ZT Quote Link to comment Share on other sites More sharing options...
VRJoe Posted June 6, 2004 Share Posted June 6, 2004 I think you can just put vacuum to both lines. From what I can tell the D solenoid sends vacuum from the dashpot if there's enough, otherwise it pulls from the vacuum bottle. I haven't gotten to that point with my LT1, but I've been thinking about it. Let us know how you make out. - Joe Quote Link to comment Share on other sites More sharing options...
technicalninja Posted June 6, 2004 Share Posted June 6, 2004 If I am understanding your post the 77 dashpot is used to slightly open throttle when compressor is on. The ZX has a similar system but its dashpot is much smaller and is located on main plenum about 3/4 the way back. This style of dash pot is not adjustable and screws directly into plenum. it has a 1/4 inch or so line coming out of it an going into the intake tubing at front of manifold. Both cars have only 2 vac lines going from HV/AC to engine. One is what I call "vacuum main" as it supplies vacuum to the system and the other is idle control through either style of dashpot. My 82 Nissan SM refers to this smaller dashpot as a F.I.C.D. (fast idle control device) and the book shows no differences between turbo and N/A. I verified this valve exists on a 81-83? ZXT manifiold I have. It is about 3 inches forward of the boost relief valve and is yellow cad plated. vacuum application opens a small fixed size port inside of valve to vent tube out of on side of valve raising idle speed slightly. Most dashpots change vacuum into mechanical movement. They don't usually supply vacuum although exceptions may exist. Hope this helps Rick Quote Link to comment Share on other sites More sharing options...
HB280ZT Posted June 7, 2004 Author Share Posted June 7, 2004 Thanks all for the info. Now technicalninja I have a part that I got from a turbo Z motor but I was not sure what it was. It has 2 ports on it a 5/16 port of the lower side and an 1/8 on the top. I have a picture of it but I can not figure out how to post it, go figure. It is not very big but it does resemble a small diaphram type item. From a picture that I have of another Turbo Z motor it is located about 3" in front of the POV/BOV and next to the forward part of the EGR. If this is the part that you are talking about then I am in luck!! Also I just noticed in the same picture that the rear vacuum take off has a little value of some kind in the line??? Is this a one way value so that when you are into boost only vacuum is let into the system?? Thanks for all your help. I really need to get this working because it really sucks not being able to at least defog the windshield when it fogs up. Thanks again!! HB280ZT Quote Link to comment Share on other sites More sharing options...
HB280ZT Posted June 9, 2004 Author Share Posted June 9, 2004 Hi All, Well I installed the FICD but I see no change in the HV/AC and I get nothing when I put a vacuum guage on the dashpot, by the way I have the lower port blocked off. Also I see vacuum on soleniods S1 and to S2 through the vacuum bottle. However I get no vacuum at soleniod D. So what do I try now??? I am not even sure if the soleniods work but I have replaced them. Can anyone give me a good diagram of how the HVAC works and what I should be seeing and where?? Also in which modes do the soleniods activate?? ie Def, heat, etc? Also I noticed on the 280ZXT they have an electric vacuum pump. Do I need to add one of these to make my setup work?? Thanks for your help. HB280ZT Quote Link to comment Share on other sites More sharing options...
technicalninja Posted June 10, 2004 Share Posted June 10, 2004 Vacuum pump is not a requirement. Good 1 way valve is. Stock 1 way valve in 280Z is acceptable. adding a secong valve at intake can help. Make sure valves are in correctly. Vacuum should be present beyond the valve when engine running. Find out which side of the valve you can suck air through (part disconnected completly from car) and place that port towards plenum. The FICD opens a passage between the plenum and the hose you have blocked off. Set up this way it will not work. The additional air has to come through the blocked off port. It should run up to a T in a larger hose that is part of the auxilary air system. This line can actually be plumbed into intake between airflow meter and turbo inlet. The FICD is not a vacuum source. It uses vacuum from the vacuum tank plumbed through one of the solinoids. This solinoid will only operate it compressor is on. If system does not have enough freon the pressure switch in receiver dryer will not allow the compressor or the FICD solinoid to operate. Get a Nissan SM for your car if you can. The factory ones are very good and it will save you money in the long run. Most aftermarket SMs are not any help except for basic repair. Rick Quote Link to comment Share on other sites More sharing options...
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