Hey guys,
I own a 2003 Z4 3.0i. Acquired in October 2018. Months ago I noticed my low coolant light had come on once. Then it started coming on frequently. I did a cooling system overhaul by myself. Pretty good for my first DIY on the car. Replaced water pump, radiator, hoses(Lower and Upper) and Belts (Water Pump and A/C compressor) and bled the system from having any air trapped in. I haven't seen a coolant light on ever since and my heat blows hot. Now it's summer time here in Philadelphia. I noticed that my A/C is not blowing cold air and I used PA Soft to diagnose the issue. I got 5 error codes from IKHE - HVAC system. 1.Pressure Sensor 2. 2-5 were all motor flap for vents and foot well. The 2-5 errors were probably occurring because I had updated the climate control system from the old one without the green lights to the one with the green lights on the knob. I'm not sure if I have to code the new climate control system in. As for pressure sensor I haven't looked upon that yet because I am not sure which one it is. I turned the A/C on to max with the snowflake button lit. Went and inspected the A/C compressor and saw the belt was spinning on the compressor but the clutch is not engaging.
How would I diagnose this issue? I have a multimeter for starters. I looked on youtube and saw a guy testing the wire to the compressor for voltage.
If I remember correctly some past posts... the temperature sensor on the lower hose is likely the culprit. It’s a easy DIY to change from below/underneath. Make sure you clean the wire connection.
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Hey Clearencediver,
The temp sensor on the lower hose? Is the lower hose for the a/c? I see that there is a sensor on the left side of the engine bay which the low pressure A/C comes out of. I have attached an image and circled what I think the sensor is. Lmk if I am wrong.
AC.jpg
Front of engine.... passenger side.
Hose from radiator....
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I would first start with the ac service because if the pressures are off nothing is going to work right
Start it normally with the car on or in position 2? Sorry for being a noob at this A/C stuff.
Have the AC system serviced... and if that doesn’t solve your issue replace the temperature sensor in that lower hose. It controls whether or not the auxiliary fan comes on. As I remember the discussion/posts it sends a signal is required to engage the AC clutch.....
I went and googled to find this... which is from the WDS (think technical manual). The discussion on the auxiliary fan is in the final paragraphs.
And a quote from WDS.
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Air conditioning
The air conditioning system is switched on by pressing the air conditioning button. The function light signals that the air conditioning system is in standby mode.
The compressor only cuts in if the switch-on conditions are fulfilled. The evaporator then produces cold air which is raised to the required temperature in reheat mode with the aid of the heat exchanger.
If a mechanically controlled compressor is installed, the evaporator cutout temperature is dependent on the outside temperature. If the outside temperature increases above 20 degrees Celsius the cutout temperature drops to 1 degrees Celsius.
To protect the evaporator from icing up, the outlet temperature is monitored by means of a sensor (evaporator sensor) and the compressor is controlled by means of an electromagnetic clutch.
Switching conditions for the electromagnetic clutch
ON (all conditions must be fulfilled)OFF (one of the conditions must be fulfilled)Timed mode (switching on and off in 20 s clock cycle)
Terminal 15 ONTerminal 15 OFFCoolant temperature greater than 117 o C and less than 120 o C
Air flow control wheeldriver out of zero positionAir flow control wheeldriver in zero position
Air conditioning standby ON (function light ON)Air conditioning standby OFF (function light OFF)
Evaporator temperature > 3 o CEvaporator temperature < 2 o C (controlled compressor < 1 o C)
Coolant temperature < 117 o CCoolant temperature > 120 o C - 3 o C hysteresis
Air conditioning system signal sent from DME (compressor ON)Full throttle signal from DME initiates shut-down with respect to time
Delay time 5 s (on reaching engine speed > 600 rpm) elapsedSpeed dropped below minimum value (400 rpm)
Pressure switch
The triple pressure switch opens the power circuit to the electromagnetic clutch when the refrigerant pressure drops below the value set for low pressure or exceeds the value set for high pressure.
Low pressureMedium pressureHigh pressure
ON < 2.8 +/- 0.2 barON > 20.0 +/- 1 barON > 33.0 +/- 1 bar
OFF > 1.9 +/- 0.2 barOFF < 17.5 +/- 1 barOFF < 23.5 +/- 1 bar
Evaporator control
The evaporator temperature controller is made up of a two-point controller on the basis of a variable positive switching threshold with 1 o K hysteresis. The refrigerant circuit is activated at an evaporator temperature > 3 o C and deactivated at an evaporator temperature < 2 o C for open-loop and at < 1 o C for controlled A/C compressor. This function prevents the evaporator from icing up.
Coolant temperature
The instrument cluster electronics (IKE) features a coolant sensor on the radiator circuit. This analog sensor signal is processed in the IKE and read in by the IHKA via the K-bus.
To avoid the engine overheating, the cooling water is monitored by the air conditioning system. At a coolant temperature above 117 o C, the electromagnetic clutch is switched on and off at 20 s intervals. If the coolant temperature exceeds 120 o C, the electromagnetic switch is switched off until the temperature drops below 117 o C. The electromagnetic clutch then cuts in once again at a rate of 100%.
Full load cutout
In order to shorten the rev-up time of the engine from idle up to full load, the electromagnetic clutch is switched off for a limited period of time at full throttle. The cutout time is between 4 and 10 s depending on the type of engine.
Full load condition: Speed signal < 14 km/h and acceleration
Idle increase (anti-stall)
To ensure smooth operation is not impaired by the compressor load, the control lines AC and KO are provided for activation of the DME by the air conditioning control unit.
When the air conditioning system is switched on, the air conditioning control unit output AC requests an idle increase from the DME. When the signal is active, the DME increases the idle speed by 110 - 200 rpm irrespective of the electromagnetic clutch.
The idle increase function (anti-stall) is additionally possible by means of coding.
Option 1: After switching on the rear window defogger, the blower in maximum setting, low beam or high beam.
Option 2: When undervoltage detected. The idle increase function is activated at terminal 30 < 11.4 V and deactivated at terminal 30 > 12.2 V.
Compressor activation
The air conditioning function is activated by pressing the A/C button. This is followed by idle increase. By way of the output DME_KO, the air conditioning control unit informs the DME that it intends to switch on the compressor. Consequently, the DME implements an interfering variable circuit, i.e. it moves the throttle in the direction "more air" while at the same time increasing the injection volume.
By way of the DME_KOREL signal (compressor relay), the DME sends a feedback message to the air conditioning control unit instructing it to switch on the A/C compressor. If all conditions for switching on the A/C compressor are fulfilled, the A/C compressor is activated directly by the control unit.
To avoid excessive water discharge from the evaporator, after the air conditioning system has been switched off while driving, the compressor is switched on and off at set intervals for 15 minutes. In this way, the evaporator temperature is slowly brought to the value of the outside temperature. This switching procedure is not necessary if controlled compressors are installed.
Auxiliary fan stage 1
The air conditioning system cuts in stage 1 of the auxiliary fan by means of relays when the compressor clutch is active and the outside temperature is greater than 10 o C. The auxiliary fan cuts out when the compressor clutch has switched off or the outside temperature is less than 8 o C.
For safety reasons, a thermostat switch also causes stage 1 to cut in at a temperature of 91 o C irrespective of the instruction given by the air conditioning control unit.
Auxiliary fan stage 2
Stage 2 of the auxiliary fan is not cut in by the air conditioning control unit.
If the cooling water exceeds a value above 99 o C or if the medium pressure switch has closed, stage 2 cuts in by means of a relay.
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So I checked out the lower radiator hose. I do not see a pressure sensor on it. This is the real oem diagram. Lmk if I am wrong and send the correct diagram. lowerhose.jpg
I was reading the WDS thing. Mentioned coolant temperature. The sensor is working correctly because I accessed the hidden cluster menu and read the readings when warm vs cold. It matches with the optimal temperatures for cold and warm but I do get a low coolant light sometimes when doing a cold start or warm start. It disappears and does not come back for the rest of the ride. Also the coolant is at MAX level and not leaking. I have bled the system. Should bleed it again? I wish I had the money for the A/C service but Drexel University hit me with that $3k Outstanding balance due to increased tuition lol. Rip wallet. Im a budget Z4 dude since im a student but I do not compromise for important aspects of the car especially in the engine bay.
This is the video I took. If it is not working try https://www.youtube.com/watch?v=7bKSmdsrNMI
Temperature sensor... part 5 on your diagram.
Clean electrical plug in connection to temperature sensor as a minimum. Replace sensor if you can afford it.
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This temperature sensor engages the electric fan....
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Interestingly on my ‘04 3.0i... my hose is installed with the temperature sensor closest to the radiator... with the sensor port pointing downward...
My diagram in realoem is the same as yours as well... which seems to be 180 degrees out.
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