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Doctor D
Doctor D, BMW Mechanic
Category: BMW
Satisfied Customers: 684
Experience:  ASE Master, 20 Years Experience
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2002 BMW 530i: auxiliary water pump..air conditioning system

Resolved Question:

I have a 2002 BMW 530i. Can the failure of the auxiliary water pump affect the operation of the vehicle's air conditioning system?
Submitted: 4 years ago.
Category: BMW
Expert:  Doctor D replied 4 years ago.
No it can not. You have replaced so many components at this point it would have been cheaper to take it to the dealer to fix the problem. Give me more info on the situation and i will try to help you.
Customer: replied 4 years ago.
I purchased the car in November of last year and thought the A/C worked but now I'm wondering if it actually did. It was cold out when I inspected the car and all I did was put my hand in front of the vent and feel cold air. I have learned that the car was in an accident and was re-built as I have discovered some electrical wiring repairs on the right front side and in the passengers door wiring harness. This past spring when I discovered that the A/C was not working I took the car to a local radiator / A/C repair facility hoping that it just needed a freon charge. They told me that the problem with the A/C was electrical and that they did not do electrical troubleshooting and or repairs. I then took the car to an independent repair facility that I had some brief experience with and thought he was trustworthy. I explained the situation to the owner of the repair facility and he said that he was experienced with performing electrical troubleshooting and repairs. His first conclusion was that he had power going to the pressure switch but not from the pressure switch to the compressor. He replaced the switch and then told me that power was leaving the pressure switch but the compressor would not come on. He said that when he jumped power to the compressor it would come on and blow cold air. He concluded that the heater control head was not properly sending the signal to the compressor. I then ordered a used heater control head unit on ebay and gave it to him for installation. He installed it and told me that the compressor came on and blew cold air for about 4 seconds and went off and would not work again. He said that he was getting a codes from remote temperature sensors (the ones that are under the front bumper near the front tires) that did not make sense, like the exterior temperature was minus 40 degress out when it was actually in the 80's. He said that these temp sensors keep the compressor from coming on and freezing up in sub zero conditions. He determined that these codes he was getting were flawed obvioulsy based on the actural temperature outside. He then told me that he thought it was a control device in the trunk near the battery (can't remember the name of it) that was not communicating with the compressor properly. He ran a jumper wire from this device to the compressor and it still would not come on. He then said it must be the evaporator sensor located in the dash behind the radio. He replaced that and it still it did not work but he said he was getting new codes and that he called the local BMW dealer and they said it could be the Auxiliary water pump. If the auxiliary water pump is not working it will not "electrically" allow the compressor to come on. My car has been with this guy all summer. I picked it up last Friday while he was supposedly trying to locate an auxiliary water pump for it. I have only paid for the parts so far which is about $300.00. He's told me that he has countless hours invested in it but has not asked me for any money yet. I have located an auxiliary water pump on line and can get one for about $160.00. I'm questioning if all or most of what he has told me over the last three months is accurate, I don't really feel that he is dishonest but I'm not sure if he is experienced enough in this kind of troubleshooting and repair, hence my email to you this morning. Mike
Expert:  Doctor D replied 4 years ago.


Good call on pulling the car. These electrical system's are very,very complex. You really are not going to be able to "accurately" fix your car without communications with the DME computer on your car. There are so many things that can turn off the a/c command signal and for various reasons. Drivability concern, temp concerns, ect.

You need to find a good independent that has a REAL BMW scanner and can communicate with the DME. A generic scanner will not do it. Otherwise all your doing is guessing and throwing parts at it. My teeth cringe when i hear about mechanics or customers back probing or jumping various sensors on the AC. This can Quickly destroy very expensive modules! This system does not operate like old school cars and uses pulse width and digital data technology and serial communication between the sensors and the various modules. Jumping, test lighting, ect can all damage the circuits and cause a very expensive repair. You will be amazed how simple the actual repair will be on your car when someone with talent and the proper scanner actually diagnosis your car. And thats assuming this last guy did not destroy anything else during his testing.

So make yourself allot of money and find a good BMW specialist in your area, or if you cant find one just bight your teeth and go to the dealer. Even the dealer will be less expensive then your last guy.

Good luck, and if you want to go over any future diagnosis with this problem I will be more then happy to go over it with you!


Customer: replied 4 years ago.

I think what your saying makes sense. I have one follow up question. The one and only time I took this car to a BMW dealer it cost me $800 with really little to show for it. They performed a lot of diagnostics and they changed the T-stat, T-stat housing, the fan blade and my windshield wiper inserts. One thing that I recently noticed on the over $3,000 list of items on the dealerships "wish list" of repairs that they said my car needed, was the Auxiliary Fan. The BMW dealer told me that it wasn't working. I asked the indenpendent mechanic about this and he said it WAS working. I have yet to see it come on myself. When I activate my A/C which ofcourse isn't blowing cold air, it doesn't seem to come on.

I' m not sure of the functions associated with the auxiliary fan but do you know if this could be a reason for the A/C not working?

Expert:  Doctor D replied 4 years ago.


It is possible but I dont think so. The Aux fan (condenser fan) will only come on as necessary to lower high side pressures. So even if it was commanded on and did not work the compressor would be turned off, however the next key cycle it would allow AC operation again. I do allot of those fans, they are available after market and are much cheaper then OE. The main complaint of that fan being bad would be "irratic" AC operation. Like waiting at a traffic light my AC starts blowing warm. If you want to go in to the dealer and just pay for a "diagnostic" maybe $100-$150 I would guess. Get all the fault codes and Diagnosis. And then maybe we can go from there.

Doctor D, BMW Mechanic
Category: BMW
Satisfied Customers: 684
Experience: ASE Master, 20 Years Experience
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