Defrost
12-12-2008, 01:17 PM
#4
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would you take some time to put in you car info, year model options, IE auto/stick
12-12-2008, 02:04 PM
#6
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Vague memory says that the failed position is for defrost - flap open with no vacuum. Should be easy to check, though, if you are checking all of the vacuum actuators.
To test the actuators, remove the side panel from the driver's side (LHD cars) of the center console. Next to the driver's ankle, there should be a bundle of colored plastic lines.
Using a sharp knife, cut each of the lines except for the black (source) and white (heater valve) lines. Test the top section (the part that goes up into the dash) to ensure that it holds vacuum. If it does, hook the cut line back together with a short piece of rubber tubing. If it doesn't hold vacuum, plug the lower section (the part that runs forward to the solenoid rack in front of the radio) until you get a round tuit to fix the leaking actuator.
Alternately, you can pull the solenoid rack and disconnect each line and test there.
To test the actuators, remove the side panel from the driver's side (LHD cars) of the center console. Next to the driver's ankle, there should be a bundle of colored plastic lines.
Using a sharp knife, cut each of the lines except for the black (source) and white (heater valve) lines. Test the top section (the part that goes up into the dash) to ensure that it holds vacuum. If it does, hook the cut line back together with a short piece of rubber tubing. If it doesn't hold vacuum, plug the lower section (the part that runs forward to the solenoid rack in front of the radio) until you get a round tuit to fix the leaking actuator.
Alternately, you can pull the solenoid rack and disconnect each line and test there.
12-12-2008, 02:42 PM
#7
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The defrost flap is open with no vacuum all years (that have one).
This is basically the opposite of all the other air flap valves...
Alan
This is basically the opposite of all the other air flap valves...
Alan
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12-12-2008, 04:40 PM
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Ok, that's what I suspected. My defrost blows air all the time. I have not done the vacuum test yet, hoping to avoid buying mightyvac just to do the test. So defrost always on points to a faulty defrost flap actuator 
Another strange behavior of the climate control is that it intermittently changes temperature on its own. It works fine for a time but occasionally starts blowing cold air even when the temp lever is all the way to the right. I assume that's not related to vacuum system. What do you guys think?
Another strange behavior of the climate control is that it intermittently changes temperature on its own. It works fine for a time but occasionally starts blowing cold air even when the temp lever is all the way to the right. I assume that's not related to vacuum system. What do you guys think?
12-12-2008, 05:33 PM
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No it sounds unrelated - probably the temp sensor loop somewhere though open circuit issues give you hot conditions. there is a full cold microswitch at the end of the temp slider - could be that is intermittent
Alan
Alan
12-12-2008, 05:48 PM
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The full cold switch is on the left of the slider isn't it? Mine intermitently goes to cold regardless of the slider position though it seems to do so more if I'm driving unevenly (sharp curves or hard brakes). I may be imagining it though.
12-12-2008, 05:54 PM
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Interesting post. I just discovered the other that all the defrost vents on my car are plugged closed with strips of black foam rubber ... so I'm adding vac actuator replacement to my 'clean up after the PO' list ... good grief!
12-12-2008, 06:06 PM
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You can do the vacuum tests with your built-in vacuum pump. Put the cut line in your mouth and carefully suck!
The HVAC system has default positions - e.g., if you lose vacuum, the default is defrost on, because that is safer. Default is heat on, because that is safer. Going to full cold is odd...
The HVAC system has default positions - e.g., if you lose vacuum, the default is defrost on, because that is safer. Default is heat on, because that is safer. Going to full cold is odd...
12-13-2008, 02:39 AM
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The fact that you have defrost all the time just means you have a leak -somewhere-. It may or may not be that actuator. Typical vacuum system failures include heat all the time, but that is often 'fixed' with a zip-tie on the heater valve, since that's easier to do than fix the vacuum problem. Other symptoms include comb flap that doesn't reatract in the center vent.
The only definitive test is with a miti-vac since you can watch the bleed-down on the gauge. Wally's suggestion of using the suction by mouth method works for gross leaks. If you have a torn actautor diaphragm that only leaks seriously when retracted, it may not show up with that method though.
The microswitch at the cold end of the slider only works when the slider is at that extreme cold position. I've never heard of one of those switches failing in the 'closed' state. You can confirm operation of the heater valve by watching it. It's under the lower air cleaner housing, on the right side (passenger side on US cars) of the car at the rear of the right cylinder head. It will go open when the engine has been shut down for a bit, goes immediately closed with the slider at cold when you start the engine. The decision to open or close the valve is made by a combination of conditions. Temp slider is not at coldest, .and. is higher than outside temp measured .and. is higher than inside temp measured. The valve will open. The actual logic is inverted with the result that the valve is closed only when slider and temps are not the above stated condition, but you get the idea.
The only definitive test is with a miti-vac since you can watch the bleed-down on the gauge. Wally's suggestion of using the suction by mouth method works for gross leaks. If you have a torn actautor diaphragm that only leaks seriously when retracted, it may not show up with that method though.
The microswitch at the cold end of the slider only works when the slider is at that extreme cold position. I've never heard of one of those switches failing in the 'closed' state. You can confirm operation of the heater valve by watching it. It's under the lower air cleaner housing, on the right side (passenger side on US cars) of the car at the rear of the right cylinder head. It will go open when the engine has been shut down for a bit, goes immediately closed with the slider at cold when you start the engine. The decision to open or close the valve is made by a combination of conditions. Temp slider is not at coldest, .and. is higher than outside temp measured .and. is higher than inside temp measured. The valve will open. The actual logic is inverted with the result that the valve is closed only when slider and temps are not the above stated condition, but you get the idea.
12-13-2008, 03:01 AM
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The cold air coming on intermitently points me to a conclusion that it's not related to vacuum. If it was a vacuum related problem, I would be getting hot air when set to cold. I'm getting cold air when slider is set to hot. The big question is this: does moving the temp slider all the way to max hot overide the outside and inside temp sensors?