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New blower and resistor - still no air flow, what next?
Hello all, I'm looking for some advice on where to go next. I replaced my squeaky HVAC blower with a new Behr unit from FCP and all was well for a few weeks. Then it stopped blowing. I took it out and bench tested the fan with 12v and it spun fine. Back in the car it went and I successfully tested it a few times during reassembly. The next day when I drove the car, I had no air flow again. After reading multiple thread I learned the fan resistor is a known failure point, I probably should have changed it along with the fan - duh. I ordered a new Beck Arnley resistor from Rock Auto and put it in. No luck, I still have no air flow. I confirmed power at the resistor so after talking to FCP to see if that fan could be the culprit, they suggested the HVAC controller might be bad. So I bought a used HVAC controller, installed it and still no fan. I verified 11.5v (with car off) 14+v with car running at the fat red/blue wire going into the resistor. I have 9.2v (car running) at the blue/grn signal wire - the one from the control unit to the resistor. **When I turn on the HVAC the fan spins slowly for approx. 5 seconds and then stops. Adjusting the fan speed, or hitting "auto" has no effect. If I cycle the HVAC on/off I get the same 5 seconds of slow fan and then nothing.
I've thrown as many parts at this problem as I can think of. Could the new resistor be bad? It's not a Behr, Bosch, it's made in Taiwan FWIW. The resistor is getting 12+ volt power and a 9v signal. What more should I be looking into?
Thanks for any help you can provide. Winter with no heat is not fun!
You can install your original squeaky blower to test and see if the new blower is the problem? If still not working you can check if any voltage at the blower terminal.
Hi Sand8,
Thanks for the reply. Unfortunately I don't have the old fan anymore, since the new one worked for about two weeks, I threw the old one away. Re. voltage - I have tested and have approx. 11.8v (with car off) at the blower terminal on the fan resistor. Again, when I turn on the HVAC, the fan will spin slowly for about 5 seconds, then stop. Bench testing the fan with a full 12v makes it spin at full speed. I am assuming that means the fan is not the culprit.
It's as if some aspect of the system is not letting the fan get a signal to run continuously. I've followed the Pelican Parts blower motor testing sequence and the last step utilizes a labscope - which I do not have, nor do I know where I can borrow one. https://www.pelicanparts.com/techart...or_Testing.htm
At this point, I'm considering buying another BEHR or similar OE resistor and seeing it it makes a difference. I hate to throw more parts at this problem, but I'm stumped.
Not for nothing, but I take it when you tested the voltage source, you physically checked the wiring and the connector? Just an off chance the carpet was removed before for some reason and the wiring to the fan motor was damaged. I have never had this problem on my 211, but had to rewire the connector on a W166 I used to have. So if the control unit is not the problem, physically check the wiring under the carpet (or wherever it may run from) that runs to the fan motor blower assembly. GL
Hey konigstiger,
A faulty control unit is what the salesperson at FCP Euro suggested. I ordered a used one (new is $1200 at local dealer) and that did not have any effect. The symptoms are the same with my old control unit and the used one I bought.
A sincere thank you for your feedback, I'm stumped so any thoughts are welcome.
As the Pelican Parts blower motor testing procedure suggests, I back probed the plug/connector at the fan resistor with a DVOM. There are 4 wires; the two large gauge ones are power for the fan (one neg, one pos.) the smaller gauge wires are the signal from the HVAC control unit. With the car off I have approx. 11.8 volts on the large positive wire, with the car running its 14+ volts. The signal wire has 9.2 volts with the car running and HVAC turned on. The Pelican parts test procedure says 'about 10v is normal for the signal wire, no matter what speed you have the fan set to' for the signal wire. So I believe I have confirmed that the resistor is getting enough voltage to run the fan, and the correct signal voltage - assuming my 9.2v is equal to "about 10v" in the Pelican test procedure I linked.
I would try to find a Xentry system. There's like, 15 different sensors that are involved with HVAC. Beyond that, I think you've done well with what you have so far with diagnostics. I think there is an HVAC reset procedure for the 211's that is legitimate. Multiple button holds and such. I think I came across one when looking into my W212 system. I'd dig into that if I had a few minutes.
I would try to find a Xentry system. There's like, 15 different sensors that are involved with HVAC. Beyond that, I think you've done well with what you have so far with diagnostics. I think there is an HVAC reset procedure for the 211's that is legitimate. Multiple button holds and such. I think I came across one when looking into my W212 system. I'd dig into that if I had a few minutes.
Thanks for the input. My HVAC cannot be reset by the methods I've found on YouTube and the forums. The procedures I've found either have you hold the defrost and recirculation buttons simultaneously, or the "rest" and "off" buttons simultaneously. My defrost and recirculation are on a rocker, so holding them both down at the same time is not possible. I have no "rest" button at all, there's just a blank on my unit where other (older?) systems have "rest".
I spoke to my Indy and they are going to take a look at the car in a few weeks. I hate to conceded defeat but without the correct system to properly diagnose this I'm stuck. In the meantime, I'm going to start looking for a MB specific system that is not too difficult to use and hopefully won't break the bank.
Thanks to all who took the time to respond. I hope to be able to return the favor some day.
I would check the connector to the blower motor, make sure it is secured and no carbon buildup. I had a burnt wire to the resistor in my other car (Cayenne) and need to make new connector and spliced about 4" back (instead of replacing the whole harness which not available locally). The funny thing is that I just replaced the blower 2 months before this happened. So, I suspected the blower motor failed again!
I would check the connector to the blower motor, make sure it is secured and no carbon buildup. I had a burnt wire to the resistor in my other car (Cayenne) and need to make new connector and spliced about 4" back (instead of replacing the whole harness which not available locally). The funny thing is that I just replaced the blower 2 months before this happened. So, I suspected the blower motor failed again!
Thanks, I'll take a look at the plug which connects to the resistor and the plug from the resistor to fan. Some Deoxit should work to make sure the full signal and fan voltage are making it through. I would be overjoyed if it's something this simple. If not, I have an appointment with my Indy shop for a few weeks from now.
Are you trying to run heat or AC? If AC (and maybe heat, as the compressor is involved with a lot of heating functions to de-humidify) and the system pressure is too low/high it may shut the system down to protect parts (compressor et al). Might have something to do with it...
Are you trying to run heat or AC? If AC (and maybe heat, as the compressor is involved with a lot of heating functions to de-humidify) and the system pressure is too low/high it may shut the system down to protect parts (compressor et al). Might have something to do with it...
Hey Senscat,
Thanks for your input. I'm trying to run the heat, not A/C. I hadn't thought of the possibility that if the compressor doesn't kick in for whatever reason, the system wouldn't allow air flow. I have been using the "auto" HVAC setting since I've owned the car and when the temps got colder I simply hit the A/C button so as to not run the compressor. *unless it's raining and I need it to dry the air. The A/C worked fine a few months ago when it was still warm enough to use it. I suppose that doesn't really mean anything however, it could have failed and I wouldn't have known.
You raise a good point, I'll mention it to my indy mechanic in a week and a half (earliest I could get the car in). I've done some HVAC and A/C work before on much simpler cars but without the correct diagnostic code reader for MB, I feel I'm in over my head on this one and will pay to have it sorted out. I'll report back once it's fixed in the hopes it helps someone else down the line.
Right on. I think you're doing the right thing getting a proper scan. These aren't grampa's old Fords. Looking forward to the solution.
In the meantime, if you had access to a gauge set, it would only take a few minutes to throw gauges on it and rule out a pressure-related fault. Not sure on Benz, but low/high refrigerant won't necessarily throw dash CEL's on a lot of cars, the sensors just shut down the compressor and stuff to prevent damage.
Right on. I think you're doing the right thing getting a proper scan. These aren't grampa's old Fords. Looking forward to the solution.
In the meantime, if you had access to a gauge set, it would only take a few minutes to throw gauges on it and rule out a pressure-related fault. Not sure on Benz, but low/high refrigerant won't necessarily throw dash CEL's on a lot of cars, the sensors just shut down the compressor and stuff to prevent damage.
I do have a manifold gauge set. If I find the time this weekend, I'll see if the compressor is kicking in and what my pressures are.
I do have a manifold gauge set. If I find the time this weekend, I'll see if the compressor is kicking in and what my pressures are.
pressures are for A/C mode only, but when the cabin heater mode is on the blower should still work with its various speeds. Controlling fans speeds on much older vehicles was done with wire wound resistors, one resistor per fan speed. 3 speeds usually but on your w211 its done with triac semiconductors and a control signal. So the RESISTOR name stuck from years past, although some sites properly list the part as a blower motor regulator or controller. Your symptoms indicate its the controller module that is mounted on the fan housing. I would only use Behr brand for longevity. 2308216451 is what I installed December 2017, But its backordered at FCP maybe there is a new part number. I had a squeaky fan motor too, replaced just that and two months later in the dead of winter I started getting erratic fan speeds, then it would mostly only work only at 2 or 3 lowest speeds, Finally crapped out altogether but the part was already on order.
pressures are for A/C mode only, but when the cabin heater mode is on the blower should still work with its various speeds. Controlling fans speeds on much older vehicles was done with wire would resistors, one resistor per fan speed. 3 speeds usually but on your w211 its done with triac semiconductors and a control signal. So the RESISTOR name stuck from years past, although some sites properly list the part as a blower motor regulator or controller. Your symptoms indicate its the controller module that is mounted on the fan housing. I would only use Behr brand for longevity. 2308216451 is what I installed December 2017, But its backordered at FCP maybe there is a new part number. I had a squeaky fan motor too, replaced just that and two months later in the dead of winter I started getting erratic fan speeds, then it would mostly only work only at 2 or 3 lowest speeds, Finally crapped out altogether but the part was already on order.
Thanks for the feedback. My fist step early on in this process was to try a new fan controller/regulator. As you said FCP, Pelican, AutoHausAZ are all sold out of the Behr brand so I got a Beck Arnley (made in Taiwan) unit. Unfortunately it did not solve my issue. The local dealers have them in stock for $380 - $500, but considering I already tried a new unit, I am hesitant to to throw a $400 part at the problem. The car goes to the mechanic on Monday, hopefully they can diagnose the issue easily.
Follow up post to close this thread and hopefully help someone else down the road. It turns out my new Behr/Mahl fan was the issue. It would bench test with 12 volts just fine, however when it was in the car and the controller scaled up the voltage, that was not enough to get it going continuously. Thankfully my independent had a w211 parts car which borrowed the fan from and put in my car. He told me diagnosing the issue was a challenge and not a common for a new fan to be faulty. That makes me feel a bit better about getting stymied by what should have been a simple fix. The award goes to Sand8 who suggested I try my old squeaky fan to rule out the fan itself as the issue. If only I had kept my old fan for a few weeks and not trashed it.........
Thanks to all who took the time to post suggestions!
I replaced my squeaking blower motor a little while ago and it would start up no issues. Replaced it with a an OEM Behr from FCP euro but kept my blower motor regulator. Fan started up no problems. Now when I turn on the blower/fan it sometimes doesn't start at all, then waits about a minute or two of driving then starts. Then if I adjust on different fan speeds it sometimes goes up and or down but sometimes doesn't do anything.
I only want to stick with Behr for the regulator but as everyone suggests it's back ordered everywhere... so I guess I can wait....
This is the message I am showing in Xentry.
The blower motor regulator is as old as the car at 13 years old. I've never had this problem prior so now I'm wondering if it could be the blower motor as mentioned above being defective... I threw the old blower motor out so I can't test anything. Would hate to buy a new blower motor just to test but the indication in Xentry shows the regulator problem.... just think it's weird that having this problem shortly after replacing the blower motor.
Pretty much currently dealing with the same parameters on my parents car.
Last year their MB had a squeaking blower motor - especially when making R/L turns.
So I ordered the BEHR OEM Blower motor from FCP, and swapped out the old OEM blower motor, and placed the 13 year old OEM MB Resistor on the new FCP/BEHR blower motor.
All has been fine w/ the HVAC for over a year of heavy use, until this week...
It's starting to get hot outside, and yesterday my father called up, and said verbatim "the A/C wasn't getting cold until at least two minutes of driving."
So, hearing that, I assumed that after 14 years, the FREON was low.
I referred them to a local independent MB shop, and told them to get the Freon recharged.
Shop recharged Freon (it was low), took it for a test drive, and the Tech experienced the same conditions that the car came in with.
Shop did a deeper probe, and have come up with the 14 year old blower motor resistor is in the process of going bad.
RE: Availability of Blower Motor Resistor: OEM Quality (i.e. Behr for $140) is on backorder everywhere, BUT you can easily get the M-B part starting at $350
The independent shop says that the ChiCom aftermarket part is garbage (they've tried it a couple of times, and it lasts only a few months) so they're going to spend the rest of the week and try to source a NEW OEM Behr part or a USED MB Part from the wrecking yards in South Sacramento.
Pretty much currently dealing with the same parameters on my parents car.
Last year their MB had a squeaking blower motor - especially when making R/L turns.
So I ordered the BEHR OEM Blower motor from FCP, and swapped out the old OEM blower motor, and placed the 13 year old OEM MB Resistor on the new FCP/BEHR blower motor.
All has been fine w/ the HVAC for over a year of heavy use, until this week...
It's starting to get hot outside, and yesterday my father called up, and said verbatim "the A/C wasn't getting cold until at least two minutes of driving."
So, hearing that, I assumed that after 14 years, the FREON was low.
I referred them to a local independent MB shop, and told them to get the Freon recharged.
Shop recharged Freon (it was low), took it for a test drive, and the Tech experienced the same conditions that the car came in with.
Shop did a deeper probe, and have come up with the 14 year old blower motor resistor is in the process of going bad.
RE: Availability of Blower Motor Resistor: OEM Quality (i.e. Behr for $140) is on backorder everywhere, BUT you can easily get the M-B part starting at $350
The independent shop says that the ChiCom aftermarket part is garbage (they've tried it a couple of times, and it lasts only a few months) so they're going to spend the rest of the week and try to source a NEW OEM Behr part or a USED MB Part from the wrecking yards in South Sacramento.
I'll update when the circle is closed.
I ended up getting the Behr blower motor regulator from Ebay from England. The dude had 5 or 6 brand new and it was actually cheaper than anything here but shipping was 20 bucks. I think total cost was $150 to get it over here which put it higher than FCP Euro but lower than Pelican Parts... Got it in about a week.
I installed it and I was still experiencing the same behavior and was super annoyed. I was doing other things with the the car and had to disconnect the battery because I broke the optical loop when I was moving wires around and then tested it again and everything works. I drove the car up to PA via memorial weekend and had the air on the entire time. It worked going up and coming back home 4 hrs each way. I keep testing it and it's fine now. Honestly not even sure what was happening. Just had the car inspected for state emissions/inspection and it passed fine.
Seems like these cars need to be driven and not sit for a long period of time even if they are in fact on a battery tender...lol
So it appears my issue is resolved. I'll hook it back up to STAR just to see if anything is out of the norm, but any time I turn on the blower it comes on and adjusts fine now with the new blower motor regulator.
I definitely didn't want to spend the $3-400 for an OEM MB behr labeled blower motor regulator only to find out it didn't work either. My guess was that perhaps the new blower motor was pulling more current or drawing more than the older one was and it was throwing the regulator off or it's just by chance that the blower motor regulator was in fact going bad...At the time I replaced the blower motor I could have ordered the regulator but choose not to since it was working prior to that, it was the slight squeak the blower motor was making that I wanted to address. But air turned on fine prior to that.
02-16-2022, 04:49 PM
New blower and resistor - still no air flow, what next?
