Climate Controls Stopped Working

[5hundred]

992 500E. I’ve been using the A/C and climate controls for the past four months of daily driving. The car was running with the A/C on when it switched to heat Yesterday on its own. Now, when I touch the HVAC controls, the fan speed and air direction do not respond.

The light in the climate control panel still illuminates (Half of them illuminate when I got the car) when the car is on, but it now blows very hot air with no way to turn it off.

Any idea on how or what to troubleshoot?

 

[gsxr]

Check all fuses first. If you have no controls at all, it sounds like lack of power.

Backlighting is separate, which is why that still works.

 

[nocfn]

Strip fuse to the line, PushButtonUnit = PBU

 

[5hundred]

Strip fuse to the line, PushButtonUnit = PBU

Check all fuses first. If you have no controls at all, it sounds like lack of power.

Backlighting is separate, which is why that still works.

Fueses are all good, attached a picture as well.

 

[5hundred]

Strip fuse to the line, PushButtonUnit = PBU

I check the fuses, picture attached here, and they are all good. What would be the next step you reccomend>?

 

[gsxr]

Did you just do a visual inspection of the fuses, or did you check each with a meter, and/or remove each to clean the contacts?

Also, there's a separate 30A strip fuse for the main HVAC fan, located outside the fuse box. On a 1992, I believe this is located at the driver strut mount.

 

[Glen]

The a/c did something similar in my car last year. On a short trip with the a/c on, it suddenly started blowing hot air. In my case, it turned out to be the PBU. Swapping PBU’s from my other 124 verified the issue.

 

[nocfn]

There is a 30amp strip fuse that blows very easy. Open hood and look for black rectangular plastic cover on or near shock tower going thru secondary firewall area on driver side. Open that up to see if the thin tungsten or aluminum strip fuse is shot. A microscopic crack is ll it takes. Search here for 30 amp fuse.

here: AC fuse | Heating and Cooling (Interior HVAC systems)

30A Strip (Leaf, Blade) Fuses | Electrical, CAN and Wiring

Everyone should have 3-4 of these 30A "strip" fuses on hand, because over time (and use) they oxidize, get soft/brittle, and eventually resistance grows to the point where they blow. Typically, this happens on the hottest days of the year, when the ambient (and underhood) temperatures are at...

www.500eboard.co

 

[gsxr]

Some additional info:

If the 30A fuse is blown/bad, only the HVAC fan will stop working, completely - zero airflow, zero fan. The rest of the system still works normally, adjusting temp between hot & cold, adjusting which vents the airflow comes from, etc etc.

If the PBU has problems or has no power, it's possible NOTHING will work - hot air all the time (default mode, it takes power to stop the hot air) and the vents default to defrost only (no footwell air, no center vent air). The PBU sends the speed signal to the blower so if the PBU isn't telling the blower to turn on, the blower may not work either.

 

[Pat]

Just finished an AC rehab, new compressor, drier and expansion valve also flushed condensor, evaporator and associated lines before doing a evacuation and freon refill. Getting nothing from the climate control unit, no fan, no ac, nothing. Has anyone used a place called ProgRama to have their climate control module rebuilt? I sent away my throttle control module to be rebuilt a few years back and had good results. My experience with various control moduals is to disconnect and reconnect certain connectors and use of some silicon spary for sliding contacts, but this module seems like I'll bust it up getting to the insides and it may be worth $280 to send it off.

 

[gsxr]

Totally dead pushbutton units are pretty rare. Have you triple-checked all the fuses? Including the 30A strip fuse for the HVAC blower?

 

[doolar]

Just finished an AC rehab, new compressor, drier and expansion valve also flushed condensor, evaporator and associated lines before doing a evacuation and freon refill. Getting nothing from the climate control unit, no fan, no ac, nothing. Has anyone used a place called ProgRama to have their climate control module rebuilt? I sent away my throttle control module to be rebuilt a few years back and had good results. My experience with various control moduals is to disconnect and reconnect certain connectors and use of some silicon spary for sliding contacts, but this module seems like I'll bust it up getting to the insides and it may be worth $280 to send it off.

I have at least two working ACC modules in my parts bin that I have zero use for, I’ll happily part with one for a reasonable price. Shipping from Sweden shouldn’t be too bad. Let me know in PM.

But double check everything else first

 

[emerydc8]

I’m thinking it’s the fan too—like @gsxr. That’s what we’re expecting to hear when we push the buttons. Once you’ve removed, checked and reinstalled (or replaced) the 30 amp strip fuse and all other fuses, if it’s still not working, maybe you can listen for the a/c compressor to engage when you push a button that would call for cold air.

Every time I’ve ever suspected the push button control unit and swapped it out, it was always some other reason I wasn’t getting the fan.

 

[Pat]

I have at least two working ACC modules in my parts bin that I have zero use for, I’ll happily part with one for a reasonable price. Shipping from Sweden shouldn’t be too bad. Let me know in PM.

But double check everything else first

Thank you for the offer, I drove the car to run some errands yesterday and after an hour or so, I had cold air coming through one vent and the auxillary fans at the condenser were spinning when I pulled in the driveway but the blower fan was still not working, so the control module is getting some of the climate controls to coordinate. I have checked the 30 amp fuse but I'll look again today to make sure the contacts are clean and from there I'll dig in to access the blower fan. Thanks again for all the helpful input.

 

[Pat]

I’m thinking it’s the fan too—like @gsxr. That’s what we’re expecting to hear when we push the buttons. Once you’ve removed, checked and reinstalled (or replaced) the 30 amp strip fuse and all other fuses, if it’s still not working, maybe you can listen for the a/c compressor to engage when you push a button that would call for cold air.

Every time I’ve ever suspected the push button control unit and swapped it out, it was always some other reason I wasn’t getting the fan.

I think you're right. Thanks for thinking it through with me. Haven't used the heat or AC for many years, here in AZ for this car it's windows up in the winter and windows down and short trips only in the summer.

 

[gsxr]

It's sounding like @emerydc8 is correct... your PBU is fine, and the problem is the HVAC blower is not working. Fuse is most likely, but next up is either the regulator or the blower motor itself. Remember you must remove the strip fuse to inspect it, yes that means removing both screws. Don't eyeball it or test with a meter.

 

[Pat]

Got it. The car loves to make me happy, so I'm sure success is near.

 

[AJ994]

Is there any news to your problem?? After two weeks in my garage, my 400E's airco is not working either. No function of the buttons (EC and re-circulating not working).... Also inspected all fuses visually, but everything looked fine I've an HHT emulation and also there no infos on any faulty clutch etc... Maybe any other adivces?

 

[gsxr]

Is there any news to your problem?? After two weeks in my garage, my 400E's airco is not working either. No function of the buttons (EC and re-circulating not working).... Also inspected all fuses visually, but everything looked fine

Do you have auto climate control, or manual? If it's auto, do the fan buttons work normally?

I've an HHT emulation and also there no infos on any faulty clutch etc... Maybe any other adivces?

HHT won't communicate digitally to the HVAC controller. There are analog blink codes available from pin #16 but don't expect any useful information.

Welcome to the forum!

 

[AJ994]

Thank you for the welcome Is there any fourm where new members introcude themselves? I do not want to be rude... Also i did not find where to enter my cars data...

I got the manual climate control. Fan works well, just position 1 is not audible and barely noticeable (thought I remembered it blowing more air before). Just the 3 buttons in the middle do not work (no red light activation and no audible activation of the "air flaps").

As said, 2 weeks before everything was working just fine.

In gerenal I know that the fault memory contains (not active in my car at the moment) an error code for the compressor clutch. If crank sensor and compressor sensor speeds do not match, there is an error code avail. in HHT. Saw that on another car....

 

[gsxr]

Thank you for the welcome Is there any fourm where new members introcude themselves? I do not want to be rude... Also i did not find where to enter my cars data...

You can start an OWNER thread with some info and photos of your car(s), if you'd like - click here.

I got the manual climate control. Fan works well, just position 1 is not audible and barely noticeable (thought I remembered it blowing more air before). Just the 3 buttons in the middle do not work (no red light activation and no audible activation of the "air flaps").

As said, 2 weeks before everything was working just fine.

Shoot. We did not get manual climate control in North America, so I'm not familiar with it. Hopefully one of our European forum members will be able to assist with diagnostics.

In gerenal I know that the fault memory contains (not active in my car at the moment) an error code for the compressor clutch. If crank sensor and compressor sensor speeds do not match, there is an error code avail. in HHT. Saw that on another car....

Correct - if there's a speed mismatch, that will be stored as a fault in the BM/GM module (pin 8). Usually that is related to belt slippage (or, less likely, AC compressor clutch slippage).

 

[AJ994]

So I just got one from the scrap yard and everything works again. Now I wanna fix the old board because the plastics, buttons etc. are in pristine condition... and maybe just get another one as backup as long as those parts are still cheap from the scrap.

I also have WIS on my PC but I find it hard to find the correct schematic to identify the output pins so I can do some measure on the PCB. MAybe anyone knows the doc-# of the correct schematic for the tempmatic (EU climate control)?