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Car Forum / Mercedes-Benz Cars / August 200789 300E AC Problems
I have an 89 300E that blows nice, cold air through the air conditioning for about 20 minutes then it turns warm. If I let the car sit for about 30 minutes, I'll get cold air again. My mechanic seems to think it may be something shutting off the compressor (short, relay, etc.). Last week, I replaced the 30amp blower motor fuse (broken) with a 40amp in-line fuse (the only one I could find). The blower works fine now but now I have the air conditioning problem described above. Could the fuse and AC problem be connected? Any thoughts? Gene Have you checked if your heater monovalve is good or bad? Sometime it does go bad and the AC cannot overcome the heat. I'm not sure where that is located or how to check it. Can you advise? >Have you checked if your heater monovalve is good or bad? Sometime it does >go bad and the AC cannot overcome the heat. > I'm not sure where that is located or how to check it. Can you advise? > [quoted text clipped - 3 lines] > -- > Message posted via CarKB.comhttp://www.carkb.com/Uwe/Forums.aspx/mercedes/200707/1 Its under the hood right where the heater hoses go into the cabin. It has an electrical connector on the top. Here's a link to one in a W126: http://articles.mbz.org/hvac/plumbing/monovalve/ That one is actually between the firewalls, but mine is not. So you may have to look around for it, but you should be able to find it by following the heater hoses into the cabin. I thought that mine might be going bad the other day, but it was another fuse that blew. It was the fuse that controlled the monovalve. (fuse 14 in mine) So you might want to check and clean all your other fuses as well. I say clean, because after I bought my car recently, I cleaned all the fuse contacts (with a pencil eraser) and it noticeably improved many electrical things. It also made my wipers start working again. Thanks Doug, If after checking the fuses I still have the problem, do you have a method of testing the monovalve? >> I'm not sure where that is located or how to check it. Can you advise? >> [quoted text clipped - 16 lines] >improved many electrical things. It also made my wipers start working >again. On your car, you got a different setup. Go to online part store like autohausaz.com and see the picture. Once you located it... you will see one side comes from engine... and the other side goes to the cabin. Grab the side that goes to the cabin... if it is warm or hot, you know it is bad. Thanks, If I understand you correctly, the monovalve can affect both the heat and cooling operations? I haven't used my heat in awhile, but I know that the last time it worked perfectly. In an earlier post, about 6 months ago, I had a problem with idling on this 1989 300E that turned out to be the O-2 sensor. I still have a moderate stumbling and surging problem at idle, after warm-up, that was present well before the O-2 sensor problem. Some of the guys mentioned checks of the ECU and pointometer. One check stood out, the check of pin 21 which is related to engine coolant temperature. Could the idle and AC problems be related in some way? The car is with my mechanic right now. I gave him printouts from this car forum of both replies related to the AC problem and the ECU/pointometer checks. Mechanics don't always like that sort of feedback and reluctantly took it. I just wanted to point him in a good general direction and share information from people whom I consider experts ( such as yourself) on this car. Thanks again, Gene >On your car, you got a different setup. Go to online part store like >autohausaz.com and see the picture. Once you located it... you will see one >side comes from engine... and the other side goes to the cabin. > >Grab the side that goes to the cabin... if it is warm or hot, you know it is >bad. In climate control system... there is two separate but interrelated system... one is AC and the other is heat. In summer, you turn on AC... when you set to the coldest, you are on pure AC only... but it would be freezing cold to tolerate... so you need some heat to temper that freezing temperature. While your AC may be operating perfectly, if the heater monovalve is bad... and let too much hot heat go through, your AC system will never be able to overcome that heat and you get just a little bit cool air. Tiger, I confirmed that the hose going to the cabin from the monovalve was not hot. This test was conducted after running the AC for about 45 minutes while idling. The auxillary fan seems to working well. It kicked on between 105- 110 C and cooled the engine down to 100 within 5 minutes. AC seems to be working okay today, except today it's not real cool while idling. However, I've been letting idle in the garage for about an hour now and it hasn't changed to warm air yet. So far, I've only noticed the problem at higway speeds. Any more thoughts? Gene >In climate control system... there is two separate but interrelated >system... one is AC and the other is heat. [quoted text clipped - 6 lines] >and let too much hot heat go through, your AC system will never be able to >overcome that heat and you get just a little bit cool air. Then I would say it is your expansion valve is bad. Idling in the garage? Are you trying to poison yourself? CO poisoniung? Either expansion valve or that your system was not properly filled with refrigerant... too low... Or when it has been filled... was not under vacuum before refilling. Tiger, Of course I had the garage door completely open while idling. I'm not sure where the expansion valve is located or how to test it. I think this car may still have R-12 refrigerant that was serviced 4 years ago by my Mercedes mechanic. Is there any way to check what refrigerant I have? After I check the expansion valve, how can you check how full it is or whether it has vacuum. By the way, did you see my other post concerning the potentiometer in this car, 1989 300E? I took it to a Volkswagon mechanic (no Mercedes mechanics in Helena, MT) yesterday for idling/surging problems. You helped me fix an O-2 sensor problem I had in December 2006. I took some of the info provided by you, T.G., and Jens in that thread and gave it to the mechanic. It concerned testing the ECU and potentiometer. The mechanic confirmed that the output reading was somewhere around 56,000 Ohms, well outside the 3,600 to 4,000 range. His book matched your findings, replace the potentiometer. Is it also called an air flow sensor? Do you agree with these findings? If so, where can I buy one? Can I go who is fair backyard mechanic do this jon without any special tools or should I just let him do it? This mechanis, while not an expert on Mercedes, seems fair and very capable of doing the job. Could the AC and potentiometer problems be linked in any way? Thanks again for your expert help, Gene >Either expansion valve or that your system was not properly filled with >refrigerant... too low... > >Or when it has been filled... was not under vacuum before refilling. Okay... now I have all the information. Right now, I would suspect you are low in refrigerant as it has been 4 years since you last checked. Whether it is R12 or 134a... is usually by the fitting on the AC line... R12 line woud have threaded connection... whereas converted system, they would install an adapter on it. I don't recall what I told you 7 months ago... why didn't you fix it back then? Surging idle can be many things... but I would start off by checking every vacuum hose in the engine... make sure they are tight fittings.... cut old section out and reinsert for tighter connection. It could be the fuel pressure regulator we were talking about... EHA... autohausaz.com has them for $277... but only change this part if it is leaking. Tiger, Where do I look for the threaded connection? An American Car Care Center mechanic was going to put refrigerant in it the other day and actually hooked the device to required connections. He said pressure appeared okay, but he did not have the AC on...he didn't know anything about Mercedes and had the climate control on "economy". he was afraid to do anything on it and sent me on my way. I didn't realize he had it on "economy" until I got donw the road. Should I just take the car to certified AC shop and have them try to fill again? The surge problem is very minor. The surge has been there for about 5 years and doesn't seem to affect performance. Just while I'm idling, sitting at traffic lights. I can see the RPM bounce up and down a notch or two. It sounds like the ECU is trying to balance fuel/air mixture. What are your thoughts on the high potentiometer reading (56,000 ohms)? I checked all vacuum connection...wen't through two cans of carb cleaner and checked every possible vacuum line for leaks. I changed both fuel pumps, filters, throttle microswitch, OVP, fuel pump relay, Beru wires, Bosch plugs, fully sythetic Mobil 1 oil has been used from day one in this car and changed before required interval. Car starts and accelarates very well. O-2 sensor change fixed the major stumbling problem in December. I used Bosch OEM O-2 sensor. I think the Volkswagon mechanic is right in suggesting replacement of the potentiometer. Should I try this first, since it will be cheaper then the fuel pressure regulator? Where can I buy one? autohausaz.com is out of stock. Thanks, Gene >Okay... now I have all the information. Right now, I would suspect you are >low in refrigerant as it has been 4 years since you last checked. Whether it [quoted text clipped - 10 lines] >autohausaz.com has them for $277... but only change this part if it is >leaking. Go to another mechanic and have him do it... He obviously don't know what he is doing as AC is AC regarless of what car it is. I'd suggest you change out that part first before fuel pressure regulator... but both can be at fault. Tiger, I talked to my actual Mercedes mechanic in Colorado and thought I could the AC conversion myself. My plan was to capture the R-12 currently in the system in an approved container, change the fittings and put the R-134 in myself using the intrsutions with the kits. Is there anything I should be concerned about during this procedure? On the potentiometer issue, is there an adjustment on that part where a guy could put the testing device on it while adjusting it to required specs? I checked all over, including the dealer, and you can't buy the potentiometer separately. Gene >Go to another mechanic and have him do it... He obviously don't know what he >is doing as AC is AC regarless of what car it is. > >I'd suggest you change out that part first before fuel pressure regulator... >but both can be at fault. > I talked to my actual Mercedes mechanic in Colorado and thought I could > the > AC conversion myself. My plan was to capture the R-12 currently in the > system in an approved container, change the fittings and put the R-134 in > myself using the intrsutions with the kits. Is there anything I should be > concerned about during this procedure? The system need to be vacuumed for at least 30 minutes... you can borrow the vacuum pump at Autozone for free. > On the potentiometer issue, is there an adjustment on that part where a > guy [quoted text clipped - 3 lines] > potentiometer > separately. The problem is I don't know what part you are referring to. Maybe if you have a picture of it then I can tell you. >>Go to another mechanic and have him do it... He obviously don't know what >>he [quoted text clipped - 3 lines] >>regulator... >>but both can be at fault. > > I talked to my actual Mercedes mechanic in Colorado and thought I could > > the [quoted text clipped - 27 lines] > > -- > > Message posted viahttp://www.carkb.com Do you mean the potentiometer for the AC? (i.e. The temp control valve.) I don't know what pot. you are talking about either. And for recovering the refrigerant, what container are you using? I am thinking of doing this also to repair some components. I will do it myself if it will save me a few hundred dollars, otherwise, I'll go to the local AC guy, and save myself the trouble. If the A/C system cools fine, don't bother switching over to R-134. There are kits sold in auto parts stores for the conversion. But if you want to do it right and keep the car for the next 5-10 years, the oil needs to be replaced too. R-12 uses mineral oil while R-134 uses either ester or PAG. Mineral oil is much thicker than Ester/PAG. R-134 molecule is smaller than R-12 so it cannot circulate mineral oil very well. A compressor without proper lubrication will not last long. Also remember that R-134 does not cool as well as R-12 in a R-12 system. Modern cars are designed with R-134 in mind. Usually the best time to convert is when a component (e.g. compressor) needs to be replaced. If it is the case, drain the oil when the old compressor is out. You can immediately tell the difference between oils. If you do not plan to service the A/C system yourself, R-12 and R-134 costs are about the same in A/C shop (since most are labor). I don't know what potentiometer you are referring to. There is a potentiometer in a W201 A/C system but it does not cause any "surge". I am not sure about W124 though it shares lots of similarities with W201. If the "surge" is in the engine, I would assume the only possible link is the mass-air flow sensor. Older cars may use a potentionmeter as the flow sensor but I don't think M103 engine uses it anymore. Anyway, potentionmeter is not adjustable. I have heard someone "repair" it by renewing the contact surface. However, I don't, and I assume most DIYers don't, have such capability/tools. > Tiger, > [quoted text clipped - 16 lines] >>I'd suggest you change out that part first before fuel pressure regulator... >>but both can be at fault. All, I'm actually diagnosing two problems with 1989 300E which could potentially be related. AC Problem: Car cools nicely for about 30 minutes then starts blowing warm air. It blows out a damp, swampy smell when it happens. I do have R12 in the system. Monovalve appears fine, checked under Tiger's guidance. Compressor has always leaked a little oil. Maybe the compressor's bad or out of oil? Not sure how to check that. Auxillary fan is working fine and AC fuse and blower motor fuse was replaced. This leads me to my next problem. Air Mass Meter: Checked by Volkswagon mechanic. He measured resistance at air flow sensor position indicator (also called potentiometer by some). The sensor position indicator is located on the front of the air mass meter. It's black with three pins on it. I think the plug that connects to it goes to the compressor (I believe). You can see a picture of it any of the parts sites and pulling up the mass air flow sensor or air mass meter. When my mechanic tested the sensor, it read off the charts (57,000 ohms instead of 3, 600 to 4,400 range). Book said to replace air flow sensor. Is there any way to fix this without buying a complete air mass meter at $650? My car is moderately stumbling and surging. It really doesn't seem to affect the performance of the car except when idling. Could these two problems (AC and idling) be related? Any more advice would be much appreciated. So far, I've gotten some great inputs from you guys. So please, keep them coming. I'm in Montana with very few Mercedes mechanics available. Thanks, v/r Gene >If the A/C system cools fine, don't bother switching over to R-134. >There are kits sold in auto parts stores for the conversion. But if you [quoted text clipped - 29 lines] >>>I'd suggest you change out that part first before fuel pressure regulator... >>>but both can be at fault. I think there are two possibilities about the A/C problem. I don't believe the air mass sensor has any relation to A/C. Possibility #1, low on freon. This should be easily identified by checking pressure on both high and low sides when the system runs. Possibility #2, loose serpentine belt (see description below). Check belt condition, tensioner, and oil at the compressor clutch (also gap). The A/C compressor has a speed sensor at its rear end. The Klima relay compares the compressor speed and the engine speed (sensor usually at ring gear around starter). When the speed deviation is too much (I saw it somewhere in the MB manual saying like 20% - 30% but can't find it anymore), it assumes the compressor is seized so it cuts off the clutch to save the belt. Therefore, the belt tension and groove condition should be checked. Also, if oil is on the clutch plate, this may cause it slip so much that the compressor speed isn't up to spec. If you see oil on the plate, degrease/wash it. The easiest way to check if it is the speed cut-off, turn off the engine and then restart. The speed comparison logic is reset by engine off. If the A/C runs again after restarting engine, it is definitely the speed cut-off. This speed comparison appears in all MB I have seen in the 80s, including W201, W126 and W124. I am not sure about earlier or later MBs though MB tends to use similar design repeatly. The air mass sensor may affect the engine speed but I would assume it also indirectly affects the compressor speed for the same degree. Therefore I do not believe there is any relation in these two problems. I am surprised to know M103 engine still uses the potentionmeter. I thought it has been replaced by the more modern thin-film type by mid-80s. The potentionmeter is a variable resistor (like fuel level sender) and the contact surface always wears out after many years of usage. > All, > [quoted text clipped - 65 lines] >>>>I'd suggest you change out that part first before fuel pressure regulator... >>>>but both can be at fault. I checked the belt for wear and slack and it appeared fine. It probably had a little more deflection then I'd like (1") but it didn't seem to be slipping while I placed a load on it. I also didn't notice any excessive oil on the compressor or clutch. There was some minor leaking coming from the power steering that was dripping onto the compressor that I cleaned. Again, it didn't appear to be causing a problem during operation. I checked the Klima relay for scoring, none noted. I did turn off the car after the AC went warm and turned it back on and it still blew warm air. Probably not the cutoff? It's most likely low freon, wouldn't you say? I've made an appointment with an AC shop and will let you know the result of pressure and coolant level. Based on Tiger's comments, I'll make sure system is vacuumed for at least 1/2 hour. On the potentiometer issue: I pulled the air cleaner off and check all hoses. I also sprayed a can of mass air flow sensor cleaner on everything and cleaned contacts. I didn't notice a change of engine speed while spraying or any loose connections. I did adjust the mixture setting on the mass air flow sensor and it did seem to improve idle. I messed with it for about an hour, ensuring I marked the original spot and number of turns before adjusting. If I went too far one way, it ran sluggish. The other way, and the engine ran rough. So by ear and a test drive, I was able to improve idle slightly. However, I think it can be better. Is ther some way to test mixture with a gauge or device while adjusting the mixture screw? Does this adjustment affect the potentiometer? I believe this adjustment is out of whack and is part of the problem. Last December, I had real stumbling problems that turned out to be a worn out O-2 sensor. With the new sensor, maybe the mixture needs to be adjusted to specs? Standing by, Thanks again, Gene >I think there are two possibilities about the A/C problem. I don't >believe the air mass sensor has any relation to A/C. [quoted text clipped - 38 lines] >>>>>I'd suggest you change out that part first before fuel pressure regulator... >>>>>but both can be at fault. You got serpentine belt... There should be ZERO flex/play. Your tensioner is shot. Change the tensioner and the shock. Tiger, I agree with you 100% that the belt tension may be causing the AC problem. I replaced the tensioner and shock in 2004 through a Mercedes shop (routine maint.). Before I replace again, I'd like to try and adjust if possible. I checked the tension scale on the tensioner and the arrow is pointing to the left of a line with a big notch in it. Can I adjust by loosening the bolt (17mm) on the top part of the bracket (between water/power steering pumps), then adjusting clockwise on the six-sided adjustment that sticks out? Or is it a lost cause? No noise, oil, greese, or other abnormality is apparent on the belt. Belt has five grooves in it. My owner's manual calls it a poly-v- belt and has a belt routing diagram on page 97. Is this the same as serpentine belt? The only other thing that's happening along with this problem is that the SRS like comes on randomly. I know the belt runs alot of things, could this be causing the SRS light to come on intermitently? I still have the surging idle problem. Any tips for adjusting the idle mixture or should I just leave this problem to the real mechanics? Gene >You got serpentine belt... There should be ZERO flex/play. Your tensioner is >shot. Change the tensioner and the shock. Looking at the part supplier... yes, you got an adjustable version of belt tensioner... Your tension should be like 1/2" play... Loosen the nut on the tensioner where your wheel pulley is... then tighten via your tensioner adjuster on the top... brass thingy... then lock it all down. It is probably all related. Loose belt cause all these problems. Tiger, I tried to tighten the belt per your instructions and tensioner adjustment would not snug up. I replaced the belt thinking that would tighten things up a bit, it didn't. I think the adjuster is maxed out. I've got everything apart in my garage, any suggestions on what to do next? I took the car to an AC shop today where they topped off the refirgerant with 1 1/4 lbs, verified pressure was good, and observed good flow through the "eye" on AC valve. After a short while, the compressor shut down. They felt that the auxillary fan should be on whenever the AC is on? They also suspected that the serpentine belt was too loose and was causing all of the problems with AC compressor shutting off and fan not coming on. So, I attemped the job myself and now I'm stuck. Please help! Gene >Looking at the part supplier... yes, you got an adjustable version of belt >tensioner... Your tension should be like 1/2" play... [quoted text clipped - 4 lines] > >It is probably all related. Loose belt cause all these problems. This is your adjuster... http://catalog.worldpac.com/zygmunt/image.jsp?title=Acc.%20Belt%20Tension%20Adj. &url=http%3A//img.eautopartscatalog.com/live/G600260237FEB.JPG This is your tensioner... http://catalog.worldpac.com/zygmunt/image.jsp?title=Accessory%20Belt%20Tensioner &url=http%3A//img.eautopartscatalog.com/live/G600041536LAS.JPG You have to loosen the big giant bolt... not the little one... but loosen the little one too. Once you do that, then you should be able to tighten up the adjuster... You might have some rust... so spray some WD40 or equivalence to loosen up that thing. so you can tighten it more... clockwise. If you can't tighten it up, then you routed the belt wrong. Tiger, Turns out the adjustor bolt and nut were stripped. It probably has been that way for some time. I took out the tensioner, shock, bracket, and adjustor so I can get a better look. I had to remove fan shroud, fan blade (not clutch), power steering pump and pulley, and water pump pulley to get to them. It was real knuckle buster without the right tools. I didn't break anything though. I've got new Febi tensioner, adjustor, shock, and mounting bracket coming on Monday. The shock was replaced three years ago by my Mercedes mechanic, but nothing else. I think the shock went bad because the tensioner was wearing out? The tensioner and shock both looked good when I took them out, but since I was in there anyway I just decided to replace everything. The belt is new and was installed exactly as I took it off and matches the diagram in my owners manual. Do you have any images of a properly installed tensioner with adjustment mechanism installed? When I took the tensioner out, the adjustor fell off the bolt so I'm not exactly sure how it goes back in. It can be put on two ways. I looked at the grease on the parts and put them back together where they matched up best...I think I've got it figured out, I just want to be sure. The adjustor/nut has a left hand twist so do I go counterclockwise to tigthen? >If you can't tighten it up, then you routed the belt wrong. Shoot me an email. Tiger, Not sure how to e-mail you. My e-mail is gdkelly@bresnan.net Thanks >Shoot me an email. |
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