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CarlT
05-21-2000, 03:25 PM
Hi everyone<p>I know for a fact that my Vacuum pump is defective, and I have a leak somewhere, but should that effect the function of my AC compressor, i.e. when I press my AC button, the compressor doesn't kick in. I'm also only getting air through the defrost vents, no floor air. I gather from reading through previous postings that this is related to the lack of vacuum. Any insight is appreciated<p>Regards<br>Carl<br>

Jon
05-21-2000, 09:43 PM
And where I live it is hot without A/C. You need the pump. My pump is also bad and air blows out the defrost vents. Try turning the fan on the lowest speed this seems to help get it started out the face vents. I understand that the vacuum motor that runs the vents is on top of the HVAC unit. If it is bad you may have to remove the dash to get to it. It may be that if you get a vac pump it might fix that problem.<p>A/C compresser has to have several things to make it have power to pull in the clutch. Temperature switch at the evaperator coil must be working. This keeps the A/C compresser from running if the outside air is lower than 41 deg. <br>Low pressure switch on the dryer keep the system from running if there is not enough pressure(low r12)in the lines. This keeps you from burning up the compresser.<br>High pressure switch(also on the dryer) does the same thing if pressure is to high.<br>There is also a diode on the compresser that may be bad. If you put a meter on the plug at the compresser with the switch on you should get your 12v's, if not the back track from there. try jumping the low pressure switch first. If it kicks in then you may need freon.<br>It could be the switch on the panel but the others are easier to check if you start at the compresser first.<br>Hope this helps.<br>Jon

Brian
05-22-2000, 11:58 AM
<i>From what I've seen/read/experienced, 9 times out of 10 the fresh air vents under the cowl may be the source of the leak - they are the most exposed to the temperature extremes. The system will work - with a hiccup or two - off of manifold vacuum only, the pump (mounted near the left shock tower, not on top of HVAC) is there to supplement vacuum in face of fluctuating manifold pressure (like when you first depress throttle). This, though, requires good vac check valve between manifold and vacuum tank. SO, might want to try plugging vac line to fresh air vents, removing cowl is pretty easy. While you're in there, check the plastic tee at the vacuum tank, they are common problem points also.<p>NOW, the evaporator temp switch - which is there to prevent icing of the evaporator, the A/C can run in any temperture (and does so on DEFROST) as long as evaporator is not frozen - is upstream of the freon pressure switches. SO, check that you have 12VDC at the pressure switch on the dryer. If you don't, replace the evap switch - very common for these to fail. Whether or not you have Freon in your system, you should have 12VDC on the upstream side of the pressure switch. If the switch is bad, it is replaced by removing the cowl, it is inserted into a hole underneath the blower motor.<p>Other posters have referred to an in-line fuse, it is located behind the little triangular-ish trim piece between the center console and the glovebox. I don't have my ETM handy, so can't remember what it feeds - worth a check though.<p>My guess is the evap switch, assuming no leaks and full freon.<p>Hope this helps!<p>Brian<br>84 733i 5speed<br>ice cold air with left side fresh air vent plugged and new evap switch<p>: Hi everyone<p>: I know for a fact that my Vacuum pump is defective, and I have a leak somewhere, but should that effect the function of my AC compressor, i.e. when I press my AC button, the compressor doesn't kick in. I'm also only getting air through the defrost vents, no floor air. I gather from reading through previous postings that this is related to the lack of vacuum. Any insight is appreciated<p>: Regards<br>: Carl<p><br></i>

CarlT
05-22-2000, 07:19 PM
<i>Thanks so far guys!<p>I've fixed on obvious leak by the expansion tank, the t piece was completely rotten...<p>The compressor engaged when I hot wired the low-pressure sensor.:)<p>My next question is, how do I go about finding where the leak is. I've only had the car for 6 months, and have no idea how long it's been dead. Is there any shops that will still recharge r12? Is there another way I can check for leaks?<p>Thanks<br>Carl<br>Carl<br></i>

Jon
05-22-2000, 09:17 PM
You will have to charge the system to check for leaks. Unfortunately this can be quite expenditure due to the freon 12 tax(thank you uncle Billy)that we all pay. If your system leaked most of the way down it will take about 2 lbs to charge it back up. The A/C mechainc can put red dye into the system and look for staining on hoses etc. You should clean your engine at the self serve car wash to release any dirt or old oil and grease so as to be able to see any of red staining from any leaks especialy around the front compressor seal. <br>The other way is to use a gas sniffer to locate the leak. Unfortunately these are hard to use on a car due to the air movement under the hood from the coolant fan.<br>And oh yes the A/C will run in the defrost mode as the heat from the blend valve keeps the evaporater switch above the 41 deg. or so says the BMW 735 shop manual. I only know what I've read so if it is wrong please let me know.<p>Hope this helps out.<br>Jon<br>

Tim
05-23-2000, 10:49 AM
<i>: From what I've seen/read/experienced, 9 times out of 10 the fresh air vents under the cowl may be the source of the leak - they are the most exposed to the temperature extremes. The system will work - with a hiccup or two - off of manifold vacuum only, the pump (mounted near the left shock tower, not on top of HVAC) is there to supplement vacuum in face of fluctuating manifold pressure (like when you first depress throttle). This, though, requires good vac check valve between manifold and vacuum tank. SO, might want to try plugging vac line to fresh air vents, removing cowl is pretty easy. While you're in there, check the plastic tee at the vacuum tank, they are common problem points also.<p>: NOW, the evaporator temp switch - which is there to prevent icing of the evaporator, the A/C can run in any temperture (and does so on DEFROST) as long as evaporator is not frozen - is upstream of the freon pressure switches. SO, check that you have 12VDC at the pressure switch on the dryer. If you don't, replace the evap switch - very common for these to fail. Whether or not you have Freon in your system, you should have 12VDC on the upstream side of the pressure switch. If the switch is bad, it is replaced by removing the cowl, it is inserted into a hole underneath the blower motor.<p>: Other posters have referred to an in-line fuse, it is located behind the little triangular-ish trim piece between the center console and the glovebox. I don't have my ETM handy, so can't remember what it feeds - worth a check though.<p>: My guess is the evap switch, assuming no leaks and full freon.<p>: Hope this helps!<p>: Brian<br>: 84 733i 5speed<br>: ice cold air with left side fresh air vent plugged and new evap switch<p>: : Hi everyone<p>: : I know for a fact that my Vacuum pump is defective, and I have a leak somewhere, but should that effect the function of my AC compressor, i.e. when I press my AC button, the compressor doesn't kick in. I'm also only getting air through the defrost vents, no floor air. I gather from reading through previous postings that this is related to the lack of vacuum. Any insight is appreciated<p>: : Regards<br>: : Carl<p>Is the evaporator temp switch the same as evaporator temp regulator or is it the evaporator temp "sensor" ??<br></i>

Brian
05-25-2000, 09:29 AM
I'm not sure what the *evaporator temperature regulator" is ... What I'm referring to, the evap temp switch, looks like a relay with a 6-8" stiff wire - a thermocouple most likely - coming out of the bottom. Under the blower motor (under the cowl), there is a "hole", for lack of a better term, that the thermocouple slides into, which then goes into the evaporator somewhere. The relay cuts power to the compressor when the evaporator is icing up ... I still can't find my damn ETM, but as I recall, if you don't have 12VDC between the switches on the drier and ground, the evaporator temp switch is bad - current flows from it (when closed) to the pressure switches .... they are all in series.<p>HTH,<p>Brian<p><br><i>: : From what I've seen/read/experienced, 9 times out of 10 the fresh air vents under the cowl may be the source of the leak - they are the most exposed to the temperature extremes. The system will work - with a hiccup or two - off of manifold vacuum only, the pump (mounted near the left shock tower, not on top of HVAC) is there to supplement vacuum in face of fluctuating manifold pressure (like when you first depress throttle). This, though, requires good vac check valve between manifold and vacuum tank. SO, might want to try plugging vac line to fresh air vents, removing cowl is pretty easy. While you're in there, check the plastic tee at the vacuum tank, they are common problem points also.<p>: : NOW, the evaporator temp switch - which is there to prevent icing of the evaporator, the A/C can run in any temperture (and does so on DEFROST) as long as evaporator is not frozen - is upstream of the freon pressure switches. SO, check that you have 12VDC at the pressure switch on the dryer. If you don't, replace the evap switch - very common for these to fail. Whether or not you have Freon in your system, you should have 12VDC on the upstream side of the pressure switch. If the switch is bad, it is replaced by removing the cowl, it is inserted into a hole underneath the blower motor.<p>: : Other posters have referred to an in-line fuse, it is located behind the little triangular-ish trim piece between the center console and the glovebox. I don't have my ETM handy, so can't remember what it feeds - worth a check though.<p>: : My guess is the evap switch, assuming no leaks and full freon.<p>: : Hope this helps!<p>: : Brian<br>: : 84 733i 5speed<br>: : ice cold air with left side fresh air vent plugged and new evap switch<p>: : : Hi everyone<p>: : : I know for a fact that my Vacuum pump is defective, and I have a leak somewhere, but should that effect the function of my AC compressor, i.e. when I press my AC button, the compressor doesn't kick in. I'm also only getting air through the defrost vents, no floor air. I gather from reading through previous postings that this is related to the lack of vacuum. Any insight is appreciated<p>: : : Regards<br>: : : Carl<p>: Is the evaporator temp switch the same as evaporator temp regulator or is it the evaporator temp "sensor" ??<p></i>


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