Polo Mk10 2019 Fan Resistor Pack

[johntheo]

The above car is on its third fresh air blower resistor pack, (2 replacements), the fan impeller spins easily by hand, the (4 speed) fan will only run on full speed (4) when the resistor pack "burns out" presumably. the resistor pack is cooled by the fan air flow, and measures ~ 42mmX32mmX10mm, don't know what the fan maximum output is but someone may be able to calculate the resistor(s) heat load in watts at the different speeds from the info, below, 1,2,3,4 are the resistor terminals, probe to probe is the M.meter's resistance but I cannot zero it.
The pollen filter was renewed.

Spare Resistor New
1 to 2	2.3	ohms
1 to 3	0.9	ohms
1 to 4	0.6	ohms
2 to 3	1.7	ohms
2 to 4	2.6	ohms
3 to 4	1.1	ohms
probe to probe	0.2	ohms
		Amps
Fan speed 1		3.9
Fan speed2		6.2
Fan speed 3		10.8
Fanspeed 4		17.0

 

[sxdave]

The voltage at fan speed 4 is quite high. Presumably this is the battery voltage. It might be worth checking the voltage at the battery terminals. I would suggest to do this with and without the engine running.

 

[johntheo]

The 17 is amps, not volts.

This may be the heat generated in the resistors for the remaining 3 speeds but if a single resistor (of 3) is used for each of the speeds 1,2&3, its strange that they all fail together and it only leaves full speed available.

Fan		Fan	Resistor
speed	Res ohm	Amps	watts
4	no resistor	17	0
3	0.6	10.8	70.0
2	0.9	6.2	34.6
1	2.3	3.9	35.0

 

[sxdave]

Sorry, my mistake - did not read properly.

 

[sxdave]

I do not know how VW do this but on other makes I have seen the resistors are in a daisy chain so that:-
The slowest of 4 speeds uses R1 + R2 + R3,
The next slowest uses R2 + R3,
Next uses R3,
Fastest uses no resistors.
With this setup a failure in R3 causes all but fastest speed to fail.

 

[brianmoooore]

I know very little about a 2019 Polo, or any other VAG stuff, but a run current of 17A for a heater fan seems extremely high. Is this a measured current?

 

[johntheo]

I do not know how VW do this but on other makes I have seen the resistors are in a daisy chain so that:-
The slowest of 4 speeds uses R1 + R2 + R3,
The next slowest uses R2 + R3,
Next uses R3,
Fastest uses no resistors.
With this setup a failure in R3 causes all but fastest speed to fail.

Yes, that's the way I would have thought of it as well, I couldn't probe them individually because the pack is wrapped with a bit of fabric so I probed them as per wiring diagram shows from E2 the fan switch so maybe the readings are correct.

 

[johntheo]

I know very little about a 2019 Polo, or any other VAG stuff, but a run current of 17A for a heater fan seems extremely high. Is this a measured current?

These are measured readings with VCDS, as its fed from the cabin power point (cigarette) then the DRLs (daylight running lights) are always on at 4.7A so I just subtracted this from all the other readings. The fan loads were definitely very high from day 1 because if in traffic with the engine stopped when using stop/start and switched from speed 2 (6.2A) my normal selected speed to speed 4 (17.0A) then the engine would/will sometimes restart.
If there is no resistance on speed 4 then the fan output is 204W @ 100% eff, 153W @ 75% or 102W @ 50%.

Had a VW Derby 30 years ago and I seem to recollect a fan load of only 3A on either of its two only speeds.

 

[sxdave]

I have been thinking about the failure and what can be learned from the failed parts. This led me to have a number of questions, the answers to which might help lead to the cause of failure....

Do the show signs of thermal stress (eg darkening/charring) or mechanical stress (cracking)?
How do the electrical properties differ on all sections between old and new parts?
Has the interval between failures of parts been approximately the same (suggests underlying cause is there from the start and not changing) or are replacements failing quicker (may indicate either something else now faulty such as the fan motor or something not quite right regarding replacement part or procedure)?

From your last post it sounds like the underlying cause has been present from the start. I too am surprised the power consumption of the fan could be around 200 Watts.

I am not sure that the method of measuring the fan currents is that accurate as I think quite a lot of other stuff may be powered up when the DRLs are on.

 

[johntheo]

Unfortunately, didn't collect car in both instances so didn't see the resistors.

The failures didn't follow any set pattern. the first failed after 2.0 years and 6018 miles which based on long term MPH (converted from KPH) of 13.7 gives a "running" life of 439 hours, the second failed less than a year later (0.73 years) after a further 2164 miles or a "running" life of 158 hrs or only 36% of the first replacement. It is now in place for just less than 6 months, ~ 108 "running hours",

I would think the fan load measurement is accurate because the VCDS measures the DRLs+whatever other loads when the ignition is switch on, I ensured all other auxiliaries were off and then measured the the total loads at the different fan spoeeds and subtracted the original load of 4.7A to give the fan loads.

 

[johntheo]

This is the battery current as measured by VCDS, negative when engine off (but ignition on) and positive with engine running (charging) but meaningless then for load measurement as the alternator is supplying all the electrical loads + the BMS managed charging rate.

IDE01836 Battery current -4.645 A

 

[sxdave]

I found this (

) on youtube - testing and disassembling a fan blower resistor from a skoda. Early on in the video the resistor values can to be 2.25 ohms, 0.85 ohms and 0.3 ohms. Later in the video, after destroying the part the conclusion is that the resistors are in series. The resistor values are similar to the you have measured. So taking the values from the video 2.25+0.85+0.3=3.4 ohms and the current you have for the slowest speed setting (3.9 amps) I get 13.26 volts, almost no voltage left to run the fan motor. From this I conclude the current readings must include some other users (probably various ECUs and associated peripheral sensors/actuators).
Also of interest is that the resistor pack has a thermal fuse that blows on overheating. The partial cut diagram you have also indicates the presence of a thermal fuse. I suspect this may be what fails in your case.
Another thing you mentioned is that the pack is wrapped in fabric. I wonder what this fabric is and if it should be present in operation (removed on installation?).

 

[johntheo]

This is what I come up with, probably incorrect. (Table 1) as the fan power will scarcely have such a jump from full speed 4 to speed 3.
The fan speed control has a 30A fuse and speed 4 is the only speed that will restart the engine (stop/start) even after a hours run so the current draw must be pretty high?

If you compare just my resistance readings (which are as shown) in Table 2 below, how does this fit with the U tube diagram and which terminal is no1 from left, are the terminals (u tube) 1,2,3&4 or 4, 3,2&1. My resistor had the terminals numbered and that's how I probed them so resistance readings+probed terminals are as shown.

Also have a look at electrical diagram in post #1.

Fan	Resistance	Circuit	Resistor		Resistance	Fan	Fan	Fan
speed	Ohms	Amps	watts		Vd	volts	Watts	Output
4	no resistor	17	0		0	12	204	100%
3	0.6	10.8	70.0		6.48	5.52	60	29%
2	0.9	6.2	34.6		5.58	6.42	40	20%
1	2.3	3.9	35.0		8.97	3.03	12	6%

Spare Resistor New
1 to 2	2.3	ohms
1 to 3	0.9	ohms
1 to 4	0.6	ohms
2 to 3	1.7	ohms
2 to 4	2.6	ohms
3 to 4	1.1	ohms
probe to probe	0.2	ohms

 

[telectrix]

replace the pollen filter. if it's blocked, the reduced airflow may be causing over heating.

 

[johntheo]

This was done after 2nd replacement and the old one looks in pristine condition compared to the ones that I change normally in other cars (every 3/4 years) with ~ X 5 times the mileage.