Results 1 to 12 of 12

Thread: AC cools then not

  1. #1
    Junior Member
    Join Date
    Aug 2016
    Location
    South Texas
    Posts
    14

    Unhappy AC cools then not

    1994 E420 ac cools and then at times blows warm air. Fan blower blows on high like at half speed but that may be a fan blower going out. My question is if anyone kniws if there is an ac relay behind fuse box licated under hood in front of drivers side. Has anyone wxoerienced this issue before and if so, any resolution suggestions? Ibstalled new ac compressor, freon levels good just dont know whatto trouble shoot next.

  2. #2
    E500 n00b nocfn's Avatar
    Join Date
    Jan 2014
    Location
    Kingwood TX
    Posts
    2,728

    Re: AC cools then not

    Perhaps the metal blade fuse is about to go. Change it out and see if that improves it. There is an electrical test of the resistor, but your fan must be getting proper current
    1994 E500
    249/275 - 8F19 or 8F32 or 8320

    1991 560 SEC
    199/268
    2014 E350 Cab 799/264

  3. #3
    E500E Guru
    Join Date
    Feb 2011
    Location
    DFW Texas
    Posts
    2,334

    Re: AC cools then not

    My guess,

    It goes out in hotestablishing weather. If you parked for a bit and restart, it will work again?

  4. The Following User Says Thank You to samiam44 For This Useful Post:

    wf758 (5 Days Ago)

  5. #4
    E500E Guru
    Join Date
    Feb 2011
    Location
    DFW Texas
    Posts
    2,334

    Re: AC cools then not

    I think the relay on the bm is failing. When the compressor runs all the time in hot weather instead of cycling, it goes haywire.
    It's an easy test and plentiful used for a low cost.

  6. #5
    E500E Guru emerydc8's Avatar
    Join Date
    May 2011
    Location
    Tucson, AZ
    Age
    52
    Posts
    1,180

    Re: AC cools then not

    Presuming the pressures check out as per the FSM, I would test the low pressure switch at the receiver/dryer by jumping it (not jumping the prongs on the switch, but the wires going to it) to see if that keeps the compressor from cutting out. If the switch is bad, or the wires are broken, it could be cutting power to the clutch and keeping the compressor from engaging.

    I think the relay that controls the compressor is inside the base module, not behind the fuse box, but it is rare to have a base module cause the problem. If you have a spare BM, it is easy to rule this out. Check for codes on the BM that would indicate the belt is slipping or broken. Does your compressor re-engage without having to turn the motor off and restart it? In my case, I was getting slipping and broken poly-v-belt codes and it would lock out the compressor completely. The only way to get it to re-engage was to restart the car.

    I think you can also bypass the interior thermostat control feature by moving the wheel to the full cold detent. That way it would always be calling for cold air.

    The low-speed fans are a different story and shouldn't cause the a/c to blow warm air.

    The interior fan blower motor is also a different story. That sounds like it could be a bad regulator under the motor, but for $100, it's worth changing the motor while you're in there too

    You might also look at some posts here about the mono-valve malfunctioning.
    Jon D.
    1994 E420
    1995 E420

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

    gsxr (5 Days Ago)

  8. #6
    Senior Member wf758's Avatar
    Join Date
    Aug 2016
    Location
    Houston Texas
    Posts
    121

    Re: AC cools then not

    Quote Originally Posted by samiam44 View Post
    My guess,

    It goes out in hotestablishing weather. If you parked for a bit and restart, it will work again?
    This is exactly what I've started experiencing, with a bit more frequency (maybe bc it is 100 in Houston!).

    Mostly happens if I've run fan on Auto or High. Less frequent of fan on low. Once it starts blowing warm air, on cooler days it will cycle back on in 5-10 mins without restarting car. If hot outside, the car has to sit some time (off) before AC will work again. Is this same issue OP has? Samiam44, have you seen that before? Any advice?

    I can't just force it to not work, so no certain way to test.


    Sent from my iPhone using Tapatalk
    1989 Carrera 4
    1992 500E

  9. #7
    E500E Guru
    Join Date
    Feb 2011
    Location
    DFW Texas
    Posts
    2,334

    Re: AC cools then not

    I've had this exact problem and it took me a couple years to figure out.. .and it was the BM. We only really had issues above 100F days which that year were the 59 consecutive above 100F. White car, tinted windows..

    It never gave any codes. Wife hated the car b/c the a/c would always go out and the worst times. I think I asked Dave where the
    relay was and he said never heard of a bm failure (at the time) related to ac. But, just drop the one out of my 500e into the 420e. Wife the next day says very quietly- I think you've fixed it-- knock on wood.

    Make sure the low speed fan is coming on as it makes a huge difference. If the fuse is out, or the harness damage, or the resistor block. Make sure they are running- it really keeps my engine happy @90c too.

    You can check the binary switch and make sure it's not bad- it has a low pressure and a high pressure cutout points. But when it blows warm air, I bet the compressor clutch is *not* engaged. I've heard of issues with the belt protection circuit or the sensor on the compressor going out..



    Michael
    Last edited by samiam44; 4 Days Ago at 07:06 AM.

  10. The Following User Says Thank You to samiam44 For This Useful Post:

    wf758 (4 Days Ago)

  11. #8
    Senior Member wf758's Avatar
    Join Date
    Aug 2016
    Location
    Houston Texas
    Posts
    121

    Re: AC cools then not

    Anybody know the proper part number for a base module for a 1992 500E?


    Sent from my iPhone using Tapatalk
    1989 Carrera 4
    1992 500E

  12. #9
    E500E Guru emerydc8's Avatar
    Join Date
    May 2011
    Location
    Tucson, AZ
    Age
    52
    Posts
    1,180

    Re: AC cools then not

    I've had this exact problem and it took me a couple years to figure out.. .and it was the BM.
    It took me a few years and a lot of parts to figure it out too. So, there are now three known instances where the BM was causing the compressor to disengage. I changed my belt, tensioner (twice -- one used, one new), compressor, expansion valve, receiver and interior temp sensor. It finally came down to the BM -- a $50 fix.

    I think the BM is the same for the E420 and 500E.

    http://www.ebay.com/itm/1994-95-MERC...9ZPCe5&vxp=mtr

    Someone correct me if I'm wrong.
    Jon D.
    1994 E420
    1995 E420

  13. The Following 3 Users Say Thank You to emerydc8 For This Useful Post:

    gsxr (4 Days Ago), Stevester 500E (4 Days Ago), wf758 (4 Days Ago)

  14. #10

    Re: AC cools then not

    I am having the same issue. I am getting the pin #8 - DTC 6-AC electromagnetic clutch (A9k1) jammed or poly-V-belt broken.

  15. #11
    E500E Guru emerydc8's Avatar
    Join Date
    May 2011
    Location
    Tucson, AZ
    Age
    52
    Posts
    1,180

    Re: AC cools then not

    I wonder if there was just a bad batch of modules that had to reach a certain age before failing. I got codes for both the slipping and broken belt, but once my a/c compressor locked out, that was it until I restarted the car. Toward the end, I would usually have to restart it several times to get it to work. I got pretty good at slipping it into N, turning the engine off, then back on and putting it back into D while traveling at 45 MPH.
    Jon D.
    1994 E420
    1995 E420

  16. The Following 2 Users Say Thank You to emerydc8 For This Useful Post:

    gsxr (4 Days Ago), Stevester 500E (4 Days Ago)

  17. #12
    Site Honcho
    Klugscheisser
    Ich bekenne mich
    nicht schuldig.
    gerryvz's Avatar
    Join Date
    Nov 2008
    Location
    The Woodlands, Texas, USA
    Posts
    15,293

    Re: AC cools then not

    Quote Originally Posted by emerydc8 View Post
    I think the BM is the same for the E420 and 500E.

    http://www.ebay.com/itm/1994-95-MERC...9ZPCe5&vxp=mtr

    Someone correct me if I'm wrong.
    Yep, the same & functionally identical Base Module across all V-8 W124 models, and W140 models with the 4.2 and 5.0 LH injection. Three and four-fuse variants, but all work identically well.

  18. The Following User Says Thank You to gerryvz For This Useful Post:

    emerydc8 (4 Days Ago)

Similar Threads

  1. Engine dies when hot, won't re-start until it cools down
    By Modpryor in forum Troubleshooting and Diagnostics
    Replies: 4
    Last Post: 02-15-2017, 04:19 PM

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
  •