Subject: Check fuse 21, then... Author: mccall52 : member since November, 2007 : 46 posts Posted on: 2009-07-14 10:51:00

Hello,

I recently had trouble with my heat not shutting off, even after replacing my heater valve with a new one. The IHKA control module supplies sufficient ground signal to the heater valves, but I still get one side full heat, the other not as cold as it should be.

First, make sure fuse 21 in the front fuse panel is OK.

After that, I found that the microswitch inside the IHKA control panel which opens to command full heat (done by dialing the driver side temperature wheel past 87 degrees f until it clicks) was malfunctioning, causing the 12v signal to open.

To test, find the small 2 or 3-pin plug (depends on year) on the rear of the IHKA control panel. It will have two green wires with brown tracer, one of those will have yellow tick marks. The one with yellow tick marks should have 12v (fuse 21) when the car is running. Leave the connector plugged in, and backprobe using a voltmeter the other green/brown wire (with no tick marks) and see if there is 12v there as well.

Mine failed this test, as the 12v signal was intermittent depending on where the temperature wheel was set. I bypassed the switch for now until I can dive in to fix it properly.

I have not had any problems with the heat staying on since. Hope this helps, since it was quite frustrating.

Thanks,
Patrick

01/90 735i Island green/Natural 245k mi.

Retrofits/Upgrades:
Passenger side power lumbar
Auto dimming rear view mirror (1991-92 style)
LED illumination upgrades in switches with failed bulbs
iL front bumper with working headlamp washers (original bumper was beat up when I bought the car)
IR keyless remote entry components, still need the remote :-(
Rebuilt heater box with brand new center section (not really upgrade per se)

01/94 M-B C280 W202.028 Light blue(348)/Dark blue (102) 113k mi.
03/96 Lincoln Town Car Executive Willow green/ivory 88k mi.

• ihka options - please help - whiteghost 2009-07-02 04:29:45 (135 views)
  • Check fuse 21, then... - mccall52 2009-07-14 10:51:00 (45 views)
  • I noticed something important last night - whiteghost 2009-07-09 15:54:26 (60 views)
  • Dumb question, but.... - cspargo 2009-07-07 01:56:52 (45 views)
  • You can rewire to override the heater valves - Patrick C 88 750 160K 2009-07-05 03:45:44 (78 views)
    • UPDATE: I checked the plug going into the water valves - whiteghost 2009-07-18 22:01:21 (18 views)
    • Can I check that the IHKA module is working by probing - whiteghost 2009-07-13 15:25:57 (26 views)
      • Yes. Best is if you can connect some electrical - Patrick C 88 750 160K 2009-07-13 21:22:59 (15 views)
    • So does this mean that by default the heater valves are open? - whiteghost 2009-07-06 02:07:01 (50 views)
      • By default the heater valves allow antifreeze to pass - Patrick C 88 750 160K 2009-07-06 21:19:51 (59 views)
        • Thank you Patrick (nt) - whiteghost 2009-07-06 22:02:14 (38 views)
  • Checked the heater valves yet? - Johan750 2009-07-02 12:06:47 (97 views)
    • please read - whiteghost 2009-07-02 13:27:36 (67 views)
    • Thank you Johan; how do you....... - whiteghost 2009-07-02 13:16:33 (72 views)
      • Hard to explain without pictures - Johan750 2009-07-03 12:20:33 (49 views)
      • one method to check is to see the pics (url) - shogun 2009-07-02 17:26:41 (72 views)
        • I think you misunderstood me Erich - whiteghost 2009-07-02 19:34:58 (63 views)
          • same procedure, check the plugs on pics - shogun 2009-07-02 23:02:43 (49 views)
  • Ihka switch unit in dash or module by sword? (nt) - dr750 2009-07-02 11:50:46 (68 views)
    • please clarify what you mean by: Ihka switch unit (nt) - whiteghost 2009-07-02 13:28:24 (57 views)
      • Ihka switch unit is in dash with fan speed switch, - dr750 2009-07-02 15:16:11 (54 views)
        • the Ihka switch unit appears to be working correctly - whiteghost 2009-07-02 15:19:38 (53 views)
          • I'm sure there would be link out there showing resoldier fixes (nt) - dr750 2009-07-02 23:57:45 (48 views)
            • I tried resoldering it last night - whiteghost 2009-07-03 01:14:29 (55 views)
              • How many pins and what color connectors? - dr750 2009-07-03 05:45:27 (49 views)