Check your radiator/condenser fan operation NOW

cidades

Veteran Member
Joined
Feb 17, 2010
Location
Portugal
TDI
Golf MK4 >> AHF(81kW)
FCM does monitor the pressure but uses it only to know:
-if the AC system is discharged, in this case compressor won't engage nor fans will turn on.
-if the high pressure line is overpressure, this disengages the compressor and turn the fans on high speed.
-if the pressure is normal, then compressor will engage and fans turn on 1st speed.


Engine temperature sense is not necessary since there is a temperature switch on radiator that bypasses my fan controller.

To drive the fans I will use a IRF4905 P-Channel MOSFET.




I have found this write up about efficient management of the fans, it looks a good approach. http://effbox.com/product/how-it-works/

The implementation is simple using a ambient temperature sensor and a condenser temperature sensor.

The algorithm is something like this:

Code:
fan_duty=50%;
loop:
     GET condenser_temp;
      IF condenser_temp >= 32ºC // ~90ºF 
                fan_duty=100%;
      ELSE
                IF condenser_temp < 21ºC // ~70ºF
                       fan_duty = 0%;
                ELSE
                       GET ambient_temp;
                       target_temp = ambient_temp + 10ºc;
                       fan_duty = fan_duty + (condenser_temp - target_temp);
                       WAIT 1sec;
GOTO loop
Makes sense?
 
Last edited:

gregoron

Member
Joined
Sep 22, 2014
Location
Honolulu
TDI
2000 Jetta
^ If I might add to above, FCM will not turn on both fans and compressor if the G65 high pressure switch is faulty. One quick way to check this is remove fuse #16 in the cabin. If the fans turn on while circuit is disconnected, then HPS might be faulty.
 

cidades

Veteran Member
Joined
Feb 17, 2010
Location
Portugal
TDI
Golf MK4 >> AHF(81kW)
^ If I might add to above, FCM will not turn on both fans and compressor if the G65 high pressure switch is faulty. One quick way to check this is remove fuse #16 in the cabin. If the fans turn on while circuit is disconnected, then HPS might be faulty.
How do you conclude that?
 

jcilforever

Veteran Member
Joined
Feb 17, 2010
Location
Southeast
TDI
2004 Jetta (SOLD), 2004 Beetle, 2003 Jetta Wagon (parts car) all manuals all for sale
Please help away fro home limited tools 90deg ac issue

Manual AC 2003 vw jetta alh wagon with car idling and AC on the clutch engages and disengages. the air won't cool. Under hood facing car right fan won't work with car at idle and AC on. AC cools when get up to speed on highway. Anyone know what to check and how to fix with limited tools, no manual, away from home. but do have VCDS with me.
 

cidades

Veteran Member
Joined
Feb 17, 2010
Location
Portugal
TDI
Golf MK4 >> AHF(81kW)
If the ambient temperature is moderate to high one fan can't maintain the condenser properly. It should be your only problem...
 

jcilforever

Veteran Member
Joined
Feb 17, 2010
Location
Southeast
TDI
2004 Jetta (SOLD), 2004 Beetle, 2003 Jetta Wagon (parts car) all manuals all for sale
Manual AC 2003 vw jetta alh wagon with car idling and AC on the clutch engages and disengages. the air won't cool. Under hood facing car right fan won't work with car at idle and AC on. AC cools when get up to speed on highway. Anyone know what to check and how to fix with limited tools, no manual, away from home. but do have VCDS with me.
Thank you to Appalachian diesel works and Dan that started this tread. tapped on my fan motor with large screw driver and it worked for split second. So I took the fan apart cleaned it then put epoxy around back and AC is as good as cold. Thank You!
 

Golf2K

Well-known member
Joined
Sep 18, 2013
Location
ONterrible
TDI
2000 Golf
2000 Golf TDI 5spd 411,000 kms

All fuses look fine

Manual A/C, was working last summer, and the A/C compressor was put in a few years ago, and the lines look good. This summer no cold air, A/C clutch doesn't engage.

I did the ignition on test with A/C on, interior fan on and the Rad fans do not turn.

I pulled of the 'Thermo Switch' Plug and jumpered 1-2 got the big fan to turn, small fan did not.

I then jumpered 2-3 on same plug, turned on ignition got nothing, tried all A/C and fan settings, fans did not spin

I hooked a battery up to the Big fan connector and it spun on both settings, the battery was weak so it didn't spin too much faster on the full speed setting, which I think is post 2-3 to a battery.

Small fan did not spin when hooked up the battery, I think I tried every which way.

Sounds like I need a New Fan assembly and possibly a Fan Control Module.

Any tips?
UPDATE:

I replaced the Aux Fan with a new Feb, and a new FCM from Uro Parts, and still nothing. I also got the car up to 93.5c Degrees and the fans did not turn on still.
 

wwshaw1

Member
Joined
Feb 22, 2013
Location
New England
TDI
2005 Passat wagon
AC fan always running

I'm hoping to be directed to the answer to my problem without having to read through 80+ pages of posts.
05 passat wagon: air conditioning works fine but the fan (the one on the engine, passenger side) runs constantly. At start up it takes a few seconds to come on and then runs the whole time I am driving, and the AC and defroster are NOT on.
Any help would be appreciated.
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
most all the good stuff is at the first page of this thread. You may have a wire grounding or a bad sensor.
Dan really did a thorough job on this
 

cidades

Veteran Member
Joined
Feb 17, 2010
Location
Portugal
TDI
Golf MK4 >> AHF(81kW)
FCM does monitor the pressure but uses it only to know:
-if the AC system is discharged, in this case compressor won't engage nor fans will turn on.
-if the high pressure line is overpressure, this disengages the compressor and turn the fans on high speed.
-if the pressure is normal, then compressor will engage and fans turn on 1st speed.


Engine temperature sense is not necessary since there is a temperature switch on radiator that bypasses my fan controller.

To drive the fans I will use a IRF4905 P-Channel MOSFET.




I have found this write up about efficient management of the fans, it looks a good approach. http://effbox.com/product/how-it-works/

The implementation is simple using a ambient temperature sensor and a condenser temperature sensor.

The algorithm is something like this:

Code:
fan_duty=50%;
loop:
     GET condenser_temp;
      IF condenser_temp >= 32ºC // ~90ºF 
                fan_duty=100%;
      ELSE
                IF condenser_temp < 21ºC // ~70ºF
                       fan_duty = 0%;
                ELSE
                       GET ambient_temp;
                       target_temp = ambient_temp + 10ºc;
                       fan_duty = fan_duty + (condenser_temp - target_temp);
                       WAIT 1sec;
GOTO loop
Makes sense?

Well I'm running a prototype on my car right now, so far it's doing just fine. With ambient temperatures bellow 17ºC the fans are completely off when the car is moving. with ambient temperatures above 28ºC the fans are at full speed(1st speed). Between about 17ºc and 25ºC when the car is moving the fans are usually at 35% duty or a little higher.

Control board:


Power MOSFET, flyback diode and condenser filter



Ambient temperature sensor:



Condenser output temperature sensor:



PICBASIC code for PIC12F683
Code:
    @    device    mclr_off
    
    ambientSensor CON 0  
    tempSensor con 3
    
                
    LED var GPIO.1              
    fan var GPIO.2                  
    
   ' Define ADCIN parameters
    Define    ADC_BITS    10    ' Set number of bits in result
    Define    ADC_CLOCK    3    ' Set clock source (3=rc)
    Define    ADC_SAMPLEUS    50    ' Set sampling time in uS
     
    rawTempData    Var    Word    
    rawAmbientTemp var word
    target_temp var word
    pwmduty var word
    temp_min var word
    temp_max var word
    tempOffset var word
     
    ADCON0.7 = 1        ' Right justify result
    ANSEL = %00111001    ' Set AN0 and AN3 analog, rest digital
    TRISIO.2=0
    CMCON0=7  ' Analog comparators off
    CMCON1 = 0
     
     hPWM 1,0,1000 
      
     'set variables
     temp_min = 43 '43 =~ 21ºc
     temp_max = 66  '66 ~= 32.2ºC                                    
     pwmduty = 127 '~50% DutyCycle
     tempOffset = 24 '~12ºC
     
     
    PwmFanControl:
    ADCIN TempSensor, rawTempData
  
    
    if rawTempData > temp_max then  
       hPWM 1,255,2000
       High led
       pwmduty = 254 ' reset pwm to max 
    else
        if rawTempData <= temp_min then    
            hPWM 1,0,2000      
            LOW LED
            sleep 1 'sleep about 2,3seg    
            High led
            pwmduty = 90' reset pwm to min speed 
        else
            ADCIN ambientSensor, rawAmbientTemp
            target_temp = rawAmbientTemp + tempOffset
            pwmduty = pwmduty + (rawTempData - target_temp)
            HIGH LED
            If pwmduty > 254 then
                 pwmduty=254
            ENDiF 
            If pwmduty < 90 then
               pwmduty=90
            ENDiF
            
            hPWM 1,pwmduty,2000
            pause 1000
            LOW LED
            pause 10
        endif
        
   endif
   
Goto PwmFanControl      


return
 

runonbeer

Maintenance EnthusiastVendor
Joined
Apr 15, 2002
Location
Austin, TX/Chapel Hill, NC
TDI
'00 Golf 02M, '10 Golf 02E, '02 UTE 02M
This is a great thread. And fantastic work by DanG

One thing that just grabbed my attention as I was using the fan troubleshooting guide for the ten-dozenth time is this:

...It is fairly easy to test the fan's response to temperature signals. Refer to section 38, page number 97-532 of the Bentley manual for the schematics,...
My Bentley actually has the AC stuff on 97-352. Surprised that nobody has caught this until now.
 

shauny88

New member
Joined
Nov 8, 2014
Location
australia
TDI
mk4
Hi all, wondering if someone can help me. I have read and referred to this thread a bunch of times and got my fans all sorted (both low speed resistors burnt out) but i am still fighting with the aircon.

Ac switch and blower on any speed and no fans run, but they will kick on when idling for a long time with no airflow, and when jumpered at the thermoswitch.

I have followed the diagnostics through and all is good except for the ac clutch voltage which is 3.5-4volts.

Jumping battery straight to ac clutch it engages and with engine and fans going gives nice cold air. Manifold gauges say pressures are perfect while jumpered and running.

Cant find any wiring issues anywhere with corrosion or breaks, so im thinking pressure switch.

I have the 3 wire duty cycle switch so cant test it as i dont have a scope.

However, unplugging fuse 16 and putting ac switch and blower fans on finally has my fans spinning.

Is this a definitive method of testing pressure sensor/switch besides this or getting a scope?
 

catodd

Active member
Joined
Jan 10, 2015
Location
Central Texas
TDI
02 Jetta GLS
Glad I ran across this post, the only fan that was working was the passenger side, had 12vdc going to the driver side fan and it was not turning. Ordered a new fan.:)
 

dremd

Veteran Member
Joined
May 31, 2007
Location
South Louisiana
TDI
06 sprinter. 03 jetta wagon premium with 6 speed ALH swap, 14 JSW
Thought I'd give a note on a fan issue that I ran across recently.
The 2 outputs from the fan control module can plug in to each other as can the inputs going to the fans. Obviously this caused a non operational fan condition.
Just something else to check if the car has no history and the fans don't work.
 

cjz

Member
Joined
Dec 28, 2014
Location
Baltimore
TDI
2004 Jetta TDI
My AC struggled towards end of summer. I decided to put it off until Spring.
After seeing this thread I checked the fans - driver's side was out.
Replaced it today. Will take apart the original fan later to see if I can determine root cause and rebuild as a spare.

Thanks
 

Stiesel

Member
Joined
Mar 25, 2014
Location
Hbg, MS
TDI
None for now
So this past summer I noticed my AC was marginally better than rolling with the windows down. Checked the compressor, no leaks and charged. I thought maybe it just needed some help, so I had the windows tinted. Minimal difference, so searched the forum and here was the problem all along.
Thanks for the saving me from the MS summer and damage to my compressor.
 

Dragos

New member
Joined
Feb 11, 2015
Location
Malmo-sweden
TDI
A6 quattro 3l tdi
Cooling fans starting with engine cold

Hi all,

For almoust a year i have a strange issue with my audi A6 quattro tdi. The cooling fans start working when the car is parked and the engine cold so my battery goes dead. I already changed a battery but it proved to be a bad move as the new one was soon killed by my doddgy fans. I even took the car to audi but they couldnt find the problem so now i have my car with a small work shop trying again to find the problem. I was thinking to sell the car but that wont be a christian thing to do as the buyer will face the same problem and not an easy one. If any of you heard about a simillar issue it will be much appreciated as i am tired of carrying a jump starter with me.Please , any ideea will help.
Thank you in advance,
Dragos - sweden
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
When this happened to me, it was one of the large fuses on top of the battery was so corroded, it was shorting out.
Also check your radiator switch.
 

passatforbus

Veteran Member
Joined
Jan 20, 2015
Location
NC
TDI
97 jetta tdi 244k stage 2 Malone Bosch injectors, 98 jetta tdi 240k injectors.
ok key on, ac button on(lights up), blower on low. no radiator fans on .
Put 12 to the fan, fans run smooth. no fuse blown on the fan control module.
#1 opened fan control module, the middle relay is not there. 2 contractors only.
#2 looked at my hi/low pressure conn. it has 4 wires witch do i jump?
#3 if i jump the radiator sensor it will cause a High fan command?
help?
 
Last edited:

UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2000 & 2003 Golf GLS (2005 Mercedes E320 CDI)
A while back I tested my wife's car. I was apprehensive abut doing so because I'd managed to whittle down the repair list (new car) to the point that the number of issues are countable on one hand:D. Anyway, I hit the AC button ON, turned the fan switch to "1" and NO radiator fan operation!:eek: I then read through this thread and find that AC won't operate when at or below freezing. Feeling better about things I waited for temps above freezing to re-test. Temps were up around 34 F, but the radiator fans still weren't coming on. So, I reluctantly added this repair issue to my list. But, then, with outside temps being much warmer I thought that I would test one more time. WORKS!

The lesson here is that whatever temperature sensors are used to signal radiator fan operation (for just AC?) are not real precise and that one is best off checking fan operation when it's significantly above freezing out.

The large fan is a bit noisy, something that I'll follow up n later.
 

jettavex

Well-known member
Joined
Jun 17, 2013
Location
Whitby, Ontario
TDI
2015 Jetta TDI
Please tell me I am not crazy...
Hello DanG144 or another knowledgable sparky,
I have read through pages and page of the thread you created concerning condenser fan troubleshooting. I am impressed with your knowledge and kindness in helping so many people. Initially I was brought to this thread while attempting to find a schematic on the system. Any links to useful information has been removed. Please kindly provide any insight you may have to my situation.
I have a 2006 Jetta A5 with a climatic HVAC control head. My fans stopped operating so I removed the assy. and applied power from the battery to the assy. harness. Still inop. Verified voltage from chassis harness, good. Applied power to the smaller fan and it ran great. I took the large fan motor apart, as I have done twice in the past, to check the brushes. All looked good so I figured the problem lies within the fan motor circuitry. For fun I reversed the polarity to the large fan and it worked in reverse to the direction indicated by the arrow and common sense to help pull the air through the rads. Figuring it was time to bite the bullet and purchase a new large fan. I plugged it into the harness and to my surprise nothing. Again applied direct battery voltage and nothing accept an initial spark when I touched my test lead to the + on the battery. Reversed leads and sure enough ran in reverse. Thinking I had a bad fan I exchanged it for another. Same experience with the 2nd Behr fan. I am loosing my mind dude! What am I doing wrong? Any advice is greatly appreciated, for any help provided. :confused:

Regards,
Jettavex
 

jettavex

Well-known member
Joined
Jun 17, 2013
Location
Whitby, Ontario
TDI
2015 Jetta TDI
Yes I am able to open post 1 links however there are more within the thread that pertain to A'5 which i need. Still lost. Thanks
 

solmog

Member
Joined
Mar 25, 2015
Location
UK
TDI
MK4 Golf 130 PD TDI
My aircon has been dead for a while and auto electricians said that signal was coming from climate control unit and aircon pump can be made to work.

I swapped fan control unit beforehand and I think they said that that unit was proven good.

I checked the plug on the side of the fans my self (as shown on here) and found that shorting it out got both fans working slow speed.

Fast speed would not work at all with second short out test, with ignition on.

Presumably I've proved my fans work, but don't know where my fast speed signal/feed is coming from.....what's immediately up stream to check?
 

dremd

Veteran Member
Joined
May 31, 2007
Location
South Louisiana
TDI
06 sprinter. 03 jetta wagon premium with 6 speed ALH swap, 14 JSW
As best as I can remember high fan speed can come from 2 places 1) duty cycle signal from the high side A/C pressure sensor 2) high coolant temp / temperature switch in the radiator near the fan control module.

As a side note this is my very least favorite part of these cars to work on. Smart enough to know it is broken but to dumb to tell you what is broken.
A huge thanks (again) To DanG for documenting and helping so much.
 

zukikat

Veteran Member
Joined
Jan 7, 2012
Location
Greater New Orleans area
TDI
2001 Jetta GLS, 2003 Jetta GLS Wagon
ok key on, ac button on(lights up), blower on low. no radiator fans on .
Put 12 to the fan, fans run smooth. no fuse blown on the fan control module.
#1 opened fan control module, the middle relay is not there. 2 contractors only.
#2 looked at my hi/low pressure conn. it has 4 wires witch do i jump?
#3 if i jump the radiator sensor it will cause a High fan command?
help?
First, thanks to the gurus for this thread!!!

Second, is there definitely a full proper charge of refrigerant in your AC system?
Low/No freon also makes the fan symptoms you described.

My AC was working properly on my way home one evening but the next day in the rain I turned the controls to defrost and never felt the usual engine load variance of the compressor engagement or any vent temperature drop from ambient/
Puzzled by this sudden and unexpected problem I stopped the car, opened the hood to check for compressor clutch engagement, and saw no compressor clutch operation or fan operation with the engine running and blower speed selector and AC button both on, all of which was working properly one day earlier.

All fuses were still good and the typical issue of the "melted fuseholder" that some people have experienced with these symptoms was still in totally normal condition and in proper working order on my car.

I found unusual signs of oily residue in an area of the engine bay which lead me to a tiny oily pin-hole in one of the metal AC lines that had allowed the system to slowly lose its' refrigerant charge overnight.

A new AC line and a complete vacuum/charge got the system running properly again...

Sometimes it's the most simple things that can be the cause of the problem rather than all those commonly complex electrical system issues we so often tend to suspect from seemingly identical symptoms.
 

Grigg3

Veteran Member
Joined
Aug 5, 2006
Location
Lexington, VA
TDI
05 Jetta wagon, 15 Golf wagon
I've only read the first several pages of 86 and didn't see it but this may have been mentioned already...

The fan can be opened and reassembled with a hammer and punch. No need for a dremel tool or JB weld. I don't have one and didn't like the idea of cutting the fan apart anyhow so just tried bending the tabs back. It really was no trouble at all and real quick.

My left side fan was not working, one brush holder slightly melted and sticky. Working now after a cleaning and smoothing of brush holder.

Thanks for all the great info in this thread! I had no idea my fan wasn't working or to check it until spotting this thread by chance while looking for info on heater fan and thermal fuse.
 
Last edited:

jrerly69

New member
Joined
May 15, 2015
Location
Sicily
TDI
2003 VW Jetta 1.9L
I have a 2003 VW Jetta TDI 1.9L. My issue is my a/c isn't blowing cold air, all it's blowing is hot air. I've checked the fuse and its good, then I checked the temp control knob to see if it was sticking in the hot temp setting but after looking at the cable by the gas pedal it was working properly. so then I figured it needs to be recharged with coolant, but when I connect the pressure gauge it reads that there is pressure, but its in the red zone of the gauge. not sure what the issue is but I figure having the pressure being in the red is the reason why my a/c isn't working. what should I do to correct this issue and or what else could be the issue if it isn't the pressure problem?

so I did this step : "Manual AC (as opposed to Climatronic AC or Climatic AC -the transmission type is immaterial) cars, push the AC button in, place a fan in slow and leave your key to ON (engine does not have to be running). Both fans should run in slow (unless it is near freezing or your refrigerant pressure is too low.) If your AC light does not come on and your cabin fan does not work, do not proceed until you have troubleshot and fixed this problem; this is the primary signal to turn on the AC system."

both fans are running. so what is the next step to correct my ac? it still isn't cold at all.
 
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