HVAC Blower (Only) Acting Erratically

I was just about home when I began to have an issue with the cabin HVAC blower/fan unit. After some investigation I have narrowed down to the blower speed not responding to the CCU (Climate Control Unit). Here are my symptoms: A/C compressor (on/off) and temp responds to the selected variables. All baffles function and direct air where selected. The issue issue I am having is I cannot control fan speed and if I turn off the climate control unit as a whole the blower will still run. It turns off the a/c compressor but just blows air. If I leave it off it will intermittently change speeds or stop but comes back immediately. Could this be the result of a failing CCU, resistor, stuck relay, battery or the common ignition switch? How many of you have experienced this issue? I am baffled by the problem and it seems likely it could be any of these. I disconnected the battery in hopes the CCU will reset it self over night. On a side note. about 20 minutes after noticing the blower these three CEL lamps illuminated for a brief second: PSM, ABS, and Brake all at the same time and never came back on. I ran durametric and it did not display any fault codes. Related or unrelated. Thanks for your help and input. 1999 996 Carrera 4 98,000miles

This was the very first symptom that my ignition switch was going south. With the car started, try turning the key VERY slightly - 1 or 2 degrees - CCW and see if the fan starts behaving again. Your car will act as though possessed by demons as the switch deteriorates further.

I have read about the ignition switch keeping the HVAC blower off but nothing about keeping it running or not being able to change speeds. Would a faulty ignition switch do what i described? I did not explain that the blower will stop with the ignition power off (function normal).

What you described is precisely what mine did as the first symptom of the switch failing.

I am casting a vote for the ignition switch as well. Same symptoms, same problems, same solution. Just do it!

It's easy to jump to a faulty ignition switch just like a IMS diagnosis(or misdiagnosis). I'm gonna say blower resistor on this one based on the symptoms.

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Yea but what kind of oil is he running, ask yourself that Jack!

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Just blame M1 because its recommended by Porsche.

Alpine, 5 bucks says the ignition switch. You in? The Germans managed to miniaturize every electrical gremlin that has plagued British cars since the dawn of the internal combustion engine and entomb them in that damnable switch - I think it's a security feature intended to discourage reverse-engineering. Once they start to get out...

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Crap, my replacement ignition switch had an Audi logo on it. Does that mean my IMS is going to fail?

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Sure, why not. I mean $5 would let us drive a few spirited miles, right?

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Unfortunatley, this is going to be the norm moving forward. Same thing with Lamborghini's. Kinda cheapens the fact that you pay $150k++ and you find Audi logos everywhere. Now wouldn't be too bad if I found Lambo logo's on Porsche parts but then reliability would probably suffer.

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Yeah, but they'd be a lot more expensive if Porsche had to make all the parts.

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You mean they're not already expensive enough? :lol:

Battery....

I was watching the volt meter on the dash for the last 40 minutes home and did notice that it was holding right around 12-12.5 volts. If i remember right I think it used to float around 13.5-14 volts so a dying battery makes sense too. I might do the battery first and the switch second. I really hope the resistor is not the issue. I would hate to spend $250 for a replacement before trying the least expensive and practical PM parts first.

The low voltage sounds like your alternator or starter cable but agree you should get the battery checked out first.

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Good observation...definitely not right. Let us know what turns out to be the culprit.

You're definitely low on juice and you should investigate the charging system first. But I don't think this is the main reason to your issue. Why would a low charge prevent you from turning off the blower with the normal controls? If I don't start my car but have it in the #2 position, my voltage reads the same between 12-12.5 and I can still turn off the blower with my controls. Are you able to turn off blower when charge is at 12+ volts? Did you measure the voltage at the time you couldn't turn off the blower?

Based on everyone's responses (By the way, thank you for your input). This is beginning to seem that all responses are plausible. I am on my was this evening to Advance Auto to pick up a battery. The one I got with the car when purchased in 2010 is now 4 years old under my ownership. It needs changed anyway. The switch is in the mail via Pelican Parts along with some other PM items not related to the issue. In regards to the voltage being too low and not allowing the CCU to turn the blower off; It might be because of a complex system of relays, resistors, and capacitors that will not function properly under high or low loads of voltage. That those systems cannot close or open circuits under abnormal voltage I had a resistor fail on my GMC truck that cut the blower out on certain speeds only from a simple mechanical switch. And am assuming this system resistor works much differently based on input from a circuit board switch rather than a mechanical switch. I will keep you updated. As for bets on the issue. Keep them coming in. Too many variables for me to put money on it yet. Thanks again.

I would like to point out that it may be below 12 volts. The display does not represent a mark clearly on our cars so it is hard to tell where I am at. And I was driving too, so quick glances only. I have not put a meter on it either. But will before I change the battery.

Def put a meter on it. Once you get a new battery, measure it after you start it. If it doesn't jump above 14v as the motor is running, you most likely have a bad solenoid, alternator, cable/harness.

Charging system all checks out. Good readings all around. Cranks quicker and fires faster, so that is a positive. Initially after applying power the blower was off. I then cycled through each speed up and down. It worked perfectly. Then I shut the car off and started the engine and the blower would not turn on. It did that for the duration of the evening. Next step is replacing the ignition switch. I had the key to position #2 with the engine off and at idle and jiggled it without any response from any electrical accessories. Might be the switch is not far enough gone. There was some slight counter clockwise play though I don't really know how much should be expected.

Welp. I'm an idiot... I bought the switch thinking it was never updated. I guess i should have looked first, bought second. What is the likelihood that the updated switch will fail? I have owned the car since 68k miles/2010. And I now have logged 30k since ownership. I am going to replace anyway but am almost certain my issue extends beyond this switch. It might be the blower, resistor, or CCU. If there is a relay for any of this I am unable to locate it. Any other experiences or advise? Regards, 1999 996 Carrera 4

My guess is it's not your ignition switch but rather the "final stage resistor" of the blower fan acting up. It's part #17 here. http://www.autoatlanta.com/porsche-p...section=813-05 It's actually a transistor controlled by the a/c control unit (most likely by PWM) that controls the power to the blower to change its speed. It's an expensive item and I don't suggest you replace it just based on my guess here. Let me think about if there's a way to test it positively.

The blower resistors can be found used for $30-$50 and typically do not fail that much to be that risky to buy a newer/low mileage used one. But ultimately it's up to the owner's comfort level. You can measure the resistance between ground and the 4 pins or so. A couple will read to almost infinity if they are bad. Usually not all of them go out at once, hence the reason why you might have just one or two speeds but nothing in between.

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Um..maybe you are talking about something different but the transistor I refer to has only 3 pins and it's a power FET that controls the blower at continuous levels. There's a photo if you click the part in the link above. Were you thinking of something like the coolant fan resistor pack where there are multiple tap outs from a series of resistors? I think the OP has an automatic climate control that provides continuous blower level from OFF to full ON.

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Sorry disregard my previous testing instructions as that is for a blower resistor for another car. That's what happens when you have multiple cars.

OP, can you pls confirm you have the fully automatic HVAC control head that lets you use the "+" and "-" buttons to control the fan speed at continuous levels as opposed to a manual round **** that sets discrete levels?

It is the computerized system with the LCD display. It does have the + and - keys. http://www.suncoastparts.com/product...6_GT3_EngineAC

Looks ;like they can be had for less then $250 http://www.ebay.com/itm/New-Porsche-...-/200689107560 New! Porsche BLOWER RESISTOR (911 Boxster Cayman Carrera) oem VALEO 1059.4005 or 996.573.923.00 $179

Ok, have you run a/c diagnostic? https://rennlist.com/forums/7057458-post5.html Seems like the blower "resistor" (let's call it the driver) is the same as the VW part 1J0907521 http://www.ecstuning.com/Search/SiteSearch/1J0907521/ Still not cheap. The reason I suspect the driver is because the blower fan gets its positive power as long as the ignition switch is ON. The CCU signals the driver to ground the blower fan to turn it ON. When you turn OFF the CCU, there will be no control signal applied to the driver so it should not turn ON the fan. However, if the driver is leaking electricity, it could ground the fan and turn it ON. But once you remove the key from the ignition, you cut the positive power to the fan so it stops.

Look very very closely of this unit taken out from a 996. The VW p/n is printed on it also http://www.ebay.com/itm/Porsche-911-...a53290&vxp=mtr

Cheapest http://www.ebay.com/itm/like/221215454624?lpid=82

Thanks guys, I've got one on the way. Now to start figuring out how to pull the center counsel out. For $24.00 i would be a fool to pass it up or end up buying a $250.00 resistor. Even if it is not the issue (I hope it is).

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NICE FIND!

Update; Got the correct switch and installed but somewhere between outing the car back together the immobilizer set itself. I ran Durametric and got fault "25 W Lead". What does this mean? I have power to the car but will not crank. Is there a reset I can do? Or am I stuck Gavin to get the dealer to reset the car for me. I don't know what I did to set the immobilizer to active. I did remove the driver seat for better access under the dash. Could that have set the immobilizer? Thanks. Looks like trying to save a few hundred bucks turned into breaking about even.

Any updates?

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Check fuse E1. There are also other causes... http://www.renntech.org/forums/topic...9114/?p=199180

Update: Sorry it has taken me a while to get back. Good news. I did not need to have the car towed to my nearest dealer, Sewickley. I called them and was told that the immobilizer was not the issue of the "no crank" and that the immobilizer will not wipe codes in the car. I described the issue and was told to try and push the ignition switch in another 1/8". Sure enough it worked, it just wasn't engaged enough. So, back to the issue at hand. It turns out it is not the resistor, check that one off the list. Second attempt. I bought a used blower off a salvaged 2001 Carrera with 21,000 miles on it for $54.00. Just installed it this evening and it runs consistent now, but only on the high speed setting. It physically does not run at full speed. And will stop running at roughly 3/4 on the CCU. I think i've exhausted my options except for the most expensive and I think it might be the issue. I ran across an article in Rennlist about a 986 where the same symptoms were happening. The advice was to pull the CCU and to inspect the connections for corrosion due to condensation from the center vent. I pulled and checked out the connectors and all look fresh and clean. My only other thought to that article was that maybe the condensation made its way inside the CCU via the vent louvers close to the screen. Very plausible. I am now on the hunt for a CCU unit that won't cost me $1000.oo. I was looking on eBay but am skeptical of the condition based on their prices starting around $140.oo. Any thoughts of what else I may be overlooking? I think I've covered the whole system up to the CCU. In case any of you are attending the Pittsburgh Vintage Grand Prix this weekend (7/19), I will be in attendance with my 996 (despite this issue) and my father with his 997 turbo. Hope to see you out there. Regards, Michael 1999 996 Carrera 4 98,800 miles

Sorry to hear it's not the resistor and good luck hunting a used CCU.

FINAL REPORT: The problem has been solved and all is functioning as normal. But before I get to the final result I want to thank all that posted to solve this issue and to those who followed along. Although I spent roughly $500.00 it would be much much more if it wasn't for everyones input and part searching. I started off small and began with the typical and much discussed ignition switch. I purchased from Pelican and after pulling the driver seat to access the switch from under the dash and reinstalling, I found that the car would bot turn over. Disappointed and frustrated that the car would not start and thinking I had set the immobilizer, I almost had it towed 1.5 hours to my nearest dealer. But just before making that decision I called the shop manager and described my symptoms and what I had just done. He suggested I get back under the dash and push that switch in another 1/8 inch or so. BINGO! It worked and the car started. But after a quick outburst of joy the blower motor still did not function as normal. My next decision was to replace the blower motor resistor. I had this issue with my pickup where the blower would not function and it turned out to be a corroded resistor. So, I checked Pelican and discovered they sold for roughly $250.00! That is where you guys chimed in and found some on eBay for $25.00. So i picked one up for $25.00 and pulled the right side of the dashboard apart to replace that resistor. Again, a failed attempt, and I moved on to the next part that could be the culprit, the blower motor. Back to Pelican and realizing that the blowers run $280.00. Ouch! So I jumped on eBay again after getting such a great price on the resistor and found a seller on eBay that parts out Porsches who had a blower for $56.00 from a donor 2001 coupe with 21,000 miles. It arrived and I installed with no success again. At this point I am throwing parts at this issue, but I am being very reasonable and realistic with the prices. And I had that feeling numerous times feeling more frustrated after every attempt. The final part to replace was getting closer and closer to the climate control unit. I knew wasn't going to be easy to get or for that matter at a good price. So, I priced one on Pelican to get an idea. $1122.00 for a new CCU and I still didn't have a guarantee that it was my root cause. No way was I going to spend that much money on a new unit before confirming it was the problem. So I got back on eBay and found a few that were used but had some cosmetic problems for about $125.00 and I also found some priced up to about $750.00. I settled for one for one out of Phoenix, AZ that was a refurbished unit for $175.00 and has a $25.00 core return. It looked good and was refurbished with a 5 year warranty. So after all the money, parts and time spent on this I finally received the CCU and installed it in about 15 minutes this evening. Problem solved! The blower motor now functions as normal with all speeds functioning. Additionally all functions of the CCU work as directed. And I now have a garage full of spare parts. Anyone need a blower motor or resistor? Thanks again all.

Glad to hear you got it sorted finally and not too expensive either.

Lifting this old thread as I have more or less the same issue as mentioned here, the fan died suddenly a few days ago. The fan doesn't react on the fan speed at all from the CCU and sometimes the fan speed just goes up and down on the CCU. I have changed/checked the following things. - Replaced ignition switch - Removed the fan, it actually works with a 1.5V battery and also with 12V. - Compared the fan voltage from CCU channel 11 with another 996 and it shows the same value or slightly less. - All fuses are ok. - Changed places with relays and they are all ok. The strange thing here is that when measured the voltage from the fan connector it shows 14V when the engine is running and full fan speed from CCU. If the fan is turned off from the CCU it shows 10V and when car is turned off it shows 0V. Any ideas? Will try a different CCU when I get hold of one but it still sounds strange that there is voltage to the fan but it doesn't rotate.

Found a used CCU and now the HVAC fan is working properly. Strange thing is that now the radiator fans are also working when the snow flake is on. With the bad CCU the radiator fans didn't work even if the snow flake was on, compressor was running and AC pipes were ice cold.