Results 1 to 16 of 16

Thread: AC Compressor not engaging

  1. #1

    AC Compressor not engaging

    Hey guys,

    I just purchased my 500E and the AC doesn't work. The system had 0 pressure so under the assumption that there is a leak, I vacuumed the system, and put in 4.5 oz of R134a which brought the pressure up to around 70-75psi. I started the car, turned on the AC (temperature knob to 22 degrees, normal mode, and auto fan) but the compressor doesn't engage.

    With the pressure switch disconnected and the car started, the engine note will change when the pressure switch connector pins are shorted. However any subsequent opening and shorting of the pins do not have any affect on engine note. Also with the pressure switch disconnected and the car started, plugging in the pressure switch will change the engine note. However any subsequent unplugging and plugging back in the switch has no affect on the engine note.

    The compressor does not seem to want to turn by hand when the car is off. Is the compressor seized ?

    I appreciate your time !
    David
    Attached Images Attached Images

  2. #2
    E500E Guru
    Join Date
    Feb 2011
    Location
    DFW Texas
    Posts
    2,663

    Re: AC Compressor not engaging

    If you put a wrench on the compressor nut and it doesn't spin right... you need a compressor and associated parts.

  3. The Following 2 Users Say Thank You to samiam44 For This Useful Post:

    dorifuto.boi (06-21-2018), gsxr (06-20-2018)

  4. #3
    .036 Hoonigan™
    E500E Boffin
    gsxr's Avatar
    Join Date
    Dec 2008
    Location
    Boise, ID, USA
    Posts
    21,333

    Re: AC Compressor not engaging

    You should be able to turn the face of the compressor by hand, pretty easily. If it's hard to turn, or seized, you need a compressor. A new Denso is surprisingly affordable, under $250 last I checked from Amazon.

    The GM/BM module will compare engine RPM and compressor RPM (there's a tach sensor on the back of the compressor), and will disengage the compressor if it senses a variance in RPM's. This will also trigger an error code on the GM/BM, and will automatically re-set when the ignition is turned off/on. If your compressor turns by hand, check for this code next...

    Dave M.
    1997 E420 (Bugeyes)
    1994 E420 (Blondie)
    1994 E500 (Q-ship)
    1992 500E (Mach 5)
    1987 300D (Sportline Stage 2)
    Click here for my website
    Click here for my YouTube channel

  5. The Following User Says Thank You to gsxr For This Useful Post:

    dorifuto.boi (06-21-2018)

  6. #4
    Member salvine's Avatar
    Join Date
    Nov 2009
    Location
    WA state
    Posts
    68

    Re: AC Compressor not engaging

    The fact that was empty may also be pointing to a leak. Unfortunately our cars are prone to having leaking evaporators. Might get to mine this summer....If possible pull a vacuum again and see if you loose any. Should easily hold 30 inches for a half hour or more if there is no leak and your gauges are good.
    1992 500E face lifted with Sliver Arrow brake upgrade
    1995 M3 track toy
    2005 X5 family truckster
    1980 RX-7 first car

  7. The Following User Says Thank You to salvine For This Useful Post:

    dorifuto.boi (06-21-2018)

  8. #5
    E500E Guru emerydc8's Avatar
    Join Date
    May 2011
    Location
    Tucson, AZ
    Age
    53
    Posts
    1,313

    Re: AC Compressor not engaging

    The system had 0 pressure so under the assumption that there is a leak, I vacuumed the system, and put in 4.5 oz of R134a which brought the pressure up to around 70-75psi.
    4.5 ounces is only about 1/3 of a can. I think four cans (48 ounces) is what I used the last time I charged my system. I have found it impossible to get more than about three cans in an evacuated system without running the engine and getting the compressor to kick in and help. Even then I've had to shake the can and move it around.

    You said you vacuumed the system. Is it holding a vacuum? If not, you have a leak in the system, or it could be leaking out a Schrader valve if you have cheap gauges. If it's holding a vacuum, I'd try to get four cans in it, unless you tried Dave's test of turning the compressor by hand and it won't turn. Are you trying to turn the compressor with the belt still connected?
    Jon D.
    1994 E420
    1995 E420

  9. The Following User Says Thank You to emerydc8 For This Useful Post:

    dorifuto.boi (06-21-2018)

  10. #6

    Re: AC Compressor not engaging

    Quote Originally Posted by samiam44 View Post
    If you put a wrench on the compressor nut and it doesn't spin right... you need a compressor and associated parts.
    Quote Originally Posted by gsxr View Post
    You should be able to turn the face of the compressor by hand, pretty easily. If it's hard to turn, or seized, you need a compressor. A new Denso is surprisingly affordable, under $250 last I checked from Amazon.
    I will try to wrench on the nut. So far the face of the pulley doesn't turn by hand. The belt is still on though but that doesnt matter as the clutch should be disengaged right ?

    And I checked the price of the compressor and was very happy about what I saw.

    Quote Originally Posted by gsxr View Post
    The GM/BM module will compare engine RPM and compressor RPM (there's a tach sensor on the back of the compressor), and will disengage the compressor if it senses a variance in RPM's. This will also trigger an error code on the GM/BM, and will automatically re-set when the ignition is turned off/on. If your compressor turns by hand, check for this code next...
    Is it the N16/1 Base Module that you're referring to ?

    Quote Originally Posted by salvine View Post
    The fact that was empty may also be pointing to a leak. Unfortunately our cars are prone to having leaking evaporators. Might get to mine this summer....If possible pull a vacuum again and see if you loose any. Should easily hold 30 inches for a half hour or more if there is no leak and your gauges are good.

    Quote Originally Posted by emerydc8 View Post
    You said you vacuumed the system. Is it holding a vacuum? If not, you have a leak in the system, or it could be leaking out a Schrader valve if you have cheap gauges.
    I think my system went from 28 inches to 26 inches vacuum in half an hour. Thats why I want to fill it with UV dyed refrigerant to find the leak. Im just having trouble getting the compressor to engage in order to finish filling the system.

    Quote Originally Posted by emerydc8 View Post
    If it's holding a vacuum, I'd try to get four cans in it, unless you tried Dave's test of turning the compressor by hand and it won't turn. Are you trying to turn the compressor with the belt still connected?
    I tried turning the face of the compressor pulley by hand when the belt was still attached. Is this a method for determining whether the compressor is seized ?

  11. The Following User Says Thank You to dorifuto.boi For This Useful Post:

    TerryA (06-21-2018)

  12. #7
    .036 Hoonigan™
    E500E Boffin
    gsxr's Avatar
    Join Date
    Dec 2008
    Location
    Boise, ID, USA
    Posts
    21,333

    Re: AC Compressor not engaging

    N16/1 Base Module is also known as the Basic Module, or General module, aka BM or GM. All the same thing, it's the power supply module in the CAN box with the ATC fuses on top.

    The face of the compressor should turn easily by hand, no tools required. The clutch should be disengaged the belt should not restrict movement. With the engine running, when the compressor (clutch) engages, you should see the face of the compressor spinning. If it never spins, that's not good.

    For test purposes you can bypass the pressure switch on the receiver/drier, as the pressure switch will prevent the compressor from engaging with a low charge (or if the switch is bad). It's a combo safety switch that will also disengage the compressor if pressure is too high. If you install a new compressor, also install a new receiver / drier (OE only now), and also replace the pressure switch AND auxiliary fan switch (the red one with pigtails). Cheap insurance.


  13. The Following User Says Thank You to gsxr For This Useful Post:

    dorifuto.boi (06-21-2018)

  14. #8
    E500E Guru
    Join Date
    Feb 2011
    Location
    DFW Texas
    Posts
    2,663

    Re: AC Compressor not engaging

    Dave's on the money on this one for sure.


    For the leak- have you visually checked all the hoses, the H-valve, etc? All leak points take oil out of the system and only the evaporator and the front compressor seal might be obscured a bit. Rest are easy to find.

    2X on dave's comment. Amazon is the best place to get a NEW compressor for most ppl. He should have noted NEVER use a rebuilt. Just not worth the effort. If you go and replace a compressor, need to assess the system. Ie is there debris in the system that justifies back flushing?

    Do you have any a/c experience? if the answer is no, perhaps consider finding a good mb shop and paying for a diagnosis?

    You can jumper the compressor to run and help fill the system. You should be filling on the low side and monitoring pressure on the high-side. 1500-2000 RPM and go to a high side based on temp. SYSTEM is 2.2 lbs or 1 kg. That's exactly 2.5 14 oz cans. Most the autoparts stores have a vacuum pump and gauges under their loaner tool program.

    FYI. I thought the evaporator failure rate was more on the R12 cars where they had been converted to R134a. In the conversion they use ester oil which degraded the sealing/epoxy on the factory cores. Our 500e's came with PAG oil and R134a. I'm sure Jono or Klink will correct me ... if needed

    Michael

  15. The Following 2 Users Say Thank You to samiam44 For This Useful Post:

    dorifuto.boi (06-21-2018), gsxr (06-21-2018)

  16. #9
    Site Honcho
    Klugscheisser
    Ich bekenne mich
    nicht schuldig.
    gerryvz's Avatar
    Join Date
    Nov 2008
    Location
    Annapolis, MD
    Posts
    17,678

    Re: AC Compressor not engaging

    We could actually use some HOW-TOs on diagnosing and recharging A/C on the E500E. I've never had a single problem (never even needed to recharge my A/C) since I got my car in 2003, so never had the opportunity to do a HOW-TO.

    My G-wagen (R-134a), however, is due for some A/C maintenance, and my SEC (R-12) is due for a recharge. So, perhaps I can do a couple of HOW-TOs on this in the near future.

  17. The Following 3 Users Say Thank You to gerryvz For This Useful Post:

    dorifuto.boi (06-21-2018), gsxr (06-21-2018), nocfn (06-21-2018)

  18. #10
    E500E Guru maw1124's Avatar
    Join Date
    May 2011
    Location
    FL & MI, USA
    Age
    46
    Posts
    1,482

    Re: AC Compressor not engaging

    I agree GVZ. On this one, I almost want to start with the evap temp sensor. I posted on this before (and rather consistently), for when the air goes humid, but cool and dry on restart. I think the condensers are likely way more hearty than the sensors on these cars, but lack the empirical data to prove that thought.

    But if the engine note is changing and still no compressor, I’d suspect compressor. If it doesn’t turn by hand, that seems a giveaway. Same test, put heavy duty duct tape over the two air intakes closest to the windshield under the hood. If you get cool dry air, then it’s the sensor. If you get a changed engine note and no dry air, then compressor.

    This is cryptic, I understand, but I hope it helps.

    maw

  19. The Following 2 Users Say Thank You to maw1124 For This Useful Post:

    dorifuto.boi (06-21-2018), gsxr (06-21-2018)

  20. #11

    Re: AC Compressor not engaging

    I really appreciate everybody's time in helping me with this issue.


    Quote Originally Posted by gsxr View Post
    The face of the compressor should turn easily by hand, no tools required. The clutch should be disengaged the belt should not restrict movement. With the engine running, when the compressor (clutch) engages, you should see the face of the compressor spinning. If it never spins, that's not good.

    Quote Originally Posted by maw1124 View Post
    But if the engine note is changing and still no compressor, I’d suspect compressor. If it doesn’t turn by hand, that seems a giveaway. Same test, put heavy duty duct tape over the two air intakes closest to the windshield under the hood. If you get cool dry air, then it’s the sensor. If you get a changed engine note and no dry air, then compressor.

    I drove the car on ramps and removed the under panel to get better access to the compressor pulley. I still cannot turn the face of the pulley by hand so I am going to assume that the compressor is seized. I will get a new Denso unit from Amazon, OE drier, pressure switch, and aux fan switch. Do you guys know if there is a part diagram that I can use to look up part numbers ?


    Quote Originally Posted by samiam44 View Post
    For the leak- have you visually checked all the hoses, the H-valve, etc? All leak points take oil out of the system and only the evaporator and the front compressor seal might be obscured a bit. Rest are easy to find.


    Do you have any a/c experience? if the answer is no, perhaps consider finding a good mb shop and paying for a diagnosis?

    I have visually checked all that I can see and so far I do not see any obvious signs of refrigerant leak. Because at this point I cannot get the compressor to engage in order to fully charge the system and to run for many hours to develop a noticable leak, I will first replace the compressor and drier, refill the proper weight of refrigerant with some UV dye, and then check for leaks afterwards.


    I do not have any A/C experience but I feel that this is pretty straightforward. Have a shop evacuate my refrigerant. Replace compressor, drier, pressure switch, and aux fan switch. Vacuum the system to boil all the moisture, fill system with 1kg r134a with UV dye. Check system for leaks everyday and if a leak is found, repeat all the steps except instead of replacing components, the leak will be fixed.

  21. The Following 2 Users Say Thank You to dorifuto.boi For This Useful Post:

    gsxr (06-21-2018), maw1124 (06-22-2018)

  22. #12

    Re: AC Compressor not engaging

    These are what I found. The drier is not OEM and there are two compressors listed as OEM. I'm going to get the compressor on Amazon because its cheaper but I'm not sure which one to get.
    Attached Images Attached Images
    • File Type: png 1.png (120.6 KB, 9 views)

  23. #13
    .036 Hoonigan™
    E500E Boffin
    gsxr's Avatar
    Join Date
    Dec 2008
    Location
    Boise, ID, USA
    Posts
    21,333

    Re: AC Compressor not engaging

    Sounds like a good plan! If you have a shop do some of the work, when they vacuum the system you can check if it holds vacuum, and they might also be able to pressurize it with nitrogen and see if it holds pressure as well... before you bother squirting in refrigerant. Even so, if the evaporator as a slight leak, Cliplight Super Seal would be my first choice before an evaporator replacement. Let's hope that's not an issue. If you do have a major evaporator leak, the dye would run out of the foam drain tubes at the bottom of the HVAC box, these tubes exit above the transmission.

    For part number lookup, you'll need to get intimate with the Mercedes Electronic Parts Catalog (EPC). You can use the official, sanctioned MB version online here for $75/year fee which is the best option, but requires online access and isn't cheap. Choice #2 is buying an EPC off eBay to run on your computer, which is what I am using on my PC; this is faster (if native, and not a virtual-machine install), and doesn't require internet access. More details on both of these options are here.

    Last option is one of the online EPC's, usually of Russian origin... however these can be more difficult to navigate, sometimes lack the footnotes, and occasionally have questionable or incomplete data. They're handy in a pinch but if you expect to be using the EPC a lot, go with choice 1 or 2. Links to the Russian EPC's are here.

    EPC access is dangerous to your bank account. You've been warned. Final reading at this link about buying from online vendors, and how to figure out if a part is NLA or not.


  24. The Following User Says Thank You to gsxr For This Useful Post:

    dorifuto.boi (06-22-2018)

  25. #14
    .036 Hoonigan™
    E500E Boffin
    gsxr's Avatar
    Join Date
    Dec 2008
    Location
    Boise, ID, USA
    Posts
    21,333

    Re: AC Compressor not engaging

    Quote Originally Posted by dorifuto.boi View Post
    These are what I found. The drier is not OEM and there are two compressors listed as OEM.
    Rein will be a reboxed Chinese drier... don't do it. Read up at this link, although Rein occasionally used to rebox OEM parts, currently the odds are really poor.

    Drier p/n 124-830-03-83 is correct, MSRP is $170, Naperville has it for $126... free shipping with code 500EPROMO:
    https://www.mboemparts.com/oem-parts...tor-1248300383


    Quote Originally Posted by dorifuto.boi View Post
    I'm going to get the compressor on Amazon because its cheaper but I'm not sure which one to get.
    That reminds me! There are 2 different compressors. One with the 8-groove pulley, for early engines with manual belt tensioner... and one with 6-groove pulley, for late engines with the spring-loaded automatic tensioner. For USA models, the break was between 1992 and 1993 US model years. Since your car is a Euro import, just pop the hood and count belt pulley grooves.


  26. The Following 2 Users Say Thank You to gsxr For This Useful Post:

    dorifuto.boi (06-22-2018), maw1124 (06-22-2018)

  27. #15
    Member salvine's Avatar
    Join Date
    Nov 2009
    Location
    WA state
    Posts
    68

    Re: AC Compressor not engaging

    Sounds like you are on the right track. Evap leaks can be tricky unless they are large. Like GSXR mentioned sometimes you can dee the oil/dye dripping from the drain tubes but often I could smell the oil coming from the heater vents. If it holds vacc then you should be good. When I get to my evap job I'll try to take plenty of pictures and do a write up. I quit recharging mine a couple of years ago as it would all leak out in 24hrs
    1992 500E face lifted with Sliver Arrow brake upgrade
    1995 M3 track toy
    2005 X5 family truckster
    1980 RX-7 first car

  28. The Following 2 Users Say Thank You to salvine For This Useful Post:

    dorifuto.boi (07-01-2018), gsxr (06-22-2018)

  29. #16

    Re: AC Compressor not engaging

    I really appreciate everybody's help. You guys are so knowledgeable and I am so glad to have access to this forum.

    Quote Originally Posted by gsxr View Post
    That reminds me! There are 2 different compressors. One with the 8-groove pulley, for early engines with manual belt tensioner... and one with 6-groove pulley, for late engines with the spring-loaded automatic tensioner. For USA models, the break was between 1992 and 1993 US model years. Since your car is a Euro import, just pop the hood and count belt pulley grooves.
    I counted 8 grooves on mine so I bought the one with 8 grooves in the product photo since the descriptions for both were the same except for the part number.

    I have the compressor, pressure switch, and temperature sensor. I am waiting on UV dyed oil and drier. I was reading in the service manual and it said that if the compressor seizes, then the expansion valve and the piping at the compressor must also be replaced. I found a genuine expansion valve 1408300484 but I cannot find the part number for the piping coming out of the compressor. I got the EPC on the VM but my VM trial expired so I gotta figure that out. I also did an online search for seized compressors and seems like a lot of people say to replace the condenser as well after a compressor seizes. I found the part number of the condenser to be 1248301570 but I can't find a genuine one but I'll keep looking.

    So this week, I'm going to order an expansion valve 1408300484, look for the part number for the piping coming out of the compressor, and look for a genuine evaporator 1248301570.

    Oh also, if I have my AC system evacuated, does that mean all the oil is also taken out of the system ? Meaning if I get my system evacuated, I have to put 160ml of oil in the compressor right ?

Similar Threads

  1. Air Condition Compressor
    By Modpryor in forum Parts for Sale
    Replies: 0
    Last Post: 06-07-2018, 03:20 PM
  2. AC compressor will not engage
    By Trae in forum Heating and Cooling
    Replies: 5
    Last Post: 07-08-2015, 07:30 PM
  3. where and how much for a new 124.034 (E420) a/c compressor?
    By samiam44 in forum Heating and Cooling
    Replies: 9
    Last Post: 10-16-2012, 06:12 AM
  4. A/C Compressor Removal
    By emerydc8 in forum Heating and Cooling
    Replies: 15
    Last Post: 06-25-2012, 08:00 PM
  5. A/C compressor relay
    By tml in forum Heating and Cooling
    Replies: 4
    Last Post: 06-04-2010, 12:05 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •