cocheeze Posted February 3, 2010 Share Posted February 3, 2010 THE BACKGROUND: i have a weber in place of my stock carb, and as such the vacuum system is greatly simplified. i have two vacuum hoses: one to the distributor advance, and one to the heater's vacuum supply (the plastic canister by the firewall in the engine compartment). i have replaced the plastic canister thingy, and it did not fix this problem. THE PROBLEM: i have the heater set to defrost, but depending on rpms, the heater will alternate between blowing air on the window or through the front vents. let me clarify: low rpms (below 3500) the heater blows hot air onto me. high rpms (over 3500) the heater blows on the window. it switches back and forth as i drive, obviously. this is really annoying in rainy country, as it does a poor job of defrosting when i am idling a lot. and i deliver pizzas for a living, so i idle a lot! anyhow, i suppose my question, put simply, is: what exactly does the vacuum control in the heater linkage? also, how can i just bypass it so it is always on defrost? (defrost is all i ever use) thanks! casey Link to comment Share on other sites More sharing options...
eulogious Posted February 3, 2010 Share Posted February 3, 2010 The first thing I would look at is all the vac lines for a potential leak. It seems that the hvac isn't connected up the the reserve tank, and is somehow only getting it's vacuum off the engine, and that's why it changes, or the vac tanks doesn't hold vacuum and is just useless as the only vacuum that the HVAC system sees is that produced by the engine. Maybe there is a check valve, one that allows vacuum in but not out, that needs replacing or that is not exsistant, ie wasn't put back in after the weber conversion... I don't have my FSM on me so I can't verify that. Have you tried checking the reserve tank to see if it actually hold vacuum? Just pull the vac hose off of it and it should make a noise as air fills the reserve. When I took one off a junk yard car, it still made noise! Who knows how long it's been there, but it still had vacuum in it, so needless to say they should hold vacuum for a LONG time. If it's not holding vacuum, then I would check to see why that is. Since you replace the reserve tank already, I would say either a vacuum leak, or a bad check valve, or a bad tank if the tank doesn't hold vacuum. Other than those things, maybe the actual heater control (the buttons the choose which vents) could be bad and have a leak. It's a simple system, so there can only be a few things that can go wrong. But I would lean towards some sort of check valve/reserve tank problem... Link to comment Share on other sites More sharing options...
eulogious Posted February 3, 2010 Share Posted February 3, 2010 anyhow, i suppose my question, put simply, is: what exactly does the vacuum control in the heater linkage? also, how can i just bypass it so it is always on defrost? (defrost is all i ever use) thanks! casey The vacuum controls the movement of the vents, ie the switching between defrost and vent. I really don't know how you would bypass it to always have it on defrost, since it's all control by vacuum. I guess you could take a part your dash, find the vent levers, detach them so they aren't control by vacuum anymore and just permanently fix them in the position that you want, using a screw or something. I really don't know, I have not take the dash apart, but that is one way to solve your problem for sure. Link to comment Share on other sites More sharing options...
sube4x4 Posted February 3, 2010 Share Posted February 3, 2010 Just yank that $#!T outa there. Thats all i've ever done because they never seem to work in any old subaru i've seen. :grin:Then just cap that vacume line and call it a day. -cody Link to comment Share on other sites More sharing options...
Gloyale Posted February 3, 2010 Share Posted February 3, 2010 Just yank that $#!T outa there. Thats all i've ever done because they never seem to work in any old subaru i've seen. - Bad advice. sorry. The vac pots hardly ever fail. Problems with them ussually arrive from so yahoo blindly ripping out and capping vac lines that they don't understand. Make sure there is a reserve tank on the passenger side sturt tower, and that it is hooked to a vac supply. There should be a check vavle on the line just before the tank. If that is hooked up properly.....it should work. Worst case I supposed it COULD be the switching valve in the console leaking somewhere, but I doubt it. The way you describe it.....seems like you just need a good resevior and a check valve to keep throttle changes from affecting the vacuum present in the HVAC system. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted February 3, 2010 Share Posted February 3, 2010 Yep - sounds like a faulty check valve before the vacuum accumulator or a small leak in the system. As you open the throttle, you lose manifold vacuum - same reason the Toyota's with the faulty gas pedal have no brakes at WOT. You have no vacuum signal to retain the posistion of the HVAC actuators. The fact that this happens only at drops in manifold vacuum points to the system having a leak - either from a bad check valve or from a small leak in a line to the actuator or the heater control "button valves" in the cabin. Leaks in the tubing inside the cabin are rare since it's a hard plastic tubing for all but the connections to the controls and the actuators. GD Link to comment Share on other sites More sharing options...
cocheeze Posted February 4, 2010 Author Share Posted February 4, 2010 eulogious, gloyale, gd... correct you are! gloyale, i was the yahoo in question this time. when i removed the stock carb. and all of the lines and put in the weber, i apparently took the check valve with it. i put the check valve back in before the tank and all is well again. as usual, you guys are kicking the sh*t out of my subaru problems. thanks! casey Link to comment Share on other sites More sharing options...
eulogious Posted February 4, 2010 Share Posted February 4, 2010 Glad to see it was a simple fix and you got it going! Link to comment Share on other sites More sharing options...
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