Re: 1999 Porsche boxster radiator fans don't come on

When car is above 180 degrees the fans wont kick on unless the ac is turned on, turn ac back off and they run till temp is back down but wont come on again unless a is turned back on

Quote
jfischer45601
When car is above 180 degrees the fans wont kick on unless the ac is turned on, turn ac back off and they run till temp is back down but wont come on again unless a is turned back on

Doesn't read like a problem. Reads like the fans are behaving as they should. Maybe I'm missing something?

Fans are turned on low speed by the DME when the coolant gets hot. "Hot" is 212F this by my observation using an OBD2 code reader/data logger connected to the OBD2 port and viewing coolant temp in real time. The fans shut off when the coolant temperature gets down to 205F. If the coolant temperature climbs to 216F the fans are switched to high speed.

they wont kick on at all unless i turn the ac on, the temp keeps on climbing

i dont get low speed, nothing at all at either side radiator or engine compartment, turn on AC and all 3 come on, if i dont turn on ac the temp keeps on climbing

and observe it climb above 212F with the fans still off? My experience is it can take some idling/slow speed running to get the engine hot enough the radiator fans will switch on.

With your '99 you may be able to monitor the coolant temperature using a "hidden" feature of the A/C system.

Here:

Car diagnostic tricks which work on 1997- 2000 Boxsters.

There is some sort of serial data stream or CAN interface that allows the AC (manufactured by Audi) unit to display engine parameters. Here is a list of what can be seen:

To switch from F to C:
Hold down the recirculating button then push both the temperature + - buttons.

To access diagnostics:
Hold down the Recirculating & Air up buttons for 5 seconds.
The + - buttons go up and down through the list of "c" codes.
The center vent button switches the left display between the "c" code and its actual value.
Press the Auto button to exit.

0c - ERL
1c - Oil Temp
2c - Inside temp. Sensor mounted in the aspirator assembly at the side of the dash.
3c - Outside temp. Sensor located inside the air inlet of the A/C unit.
4c - Outside temp. Sensor located in front grill of the radiator. The data is fed to the climatronic from the instrument cluster. When not moving, the instrument cluster OBC temp display retains it's last setting until moving. This is to prevent heat emanating from the radiator affecting the temp. sensor. The A/C unit uses the lower of the two outside air temp values in determining fresh-air temp.
5c - Outside temp. (matches with OBC outside temp display)
#################
6c - Coolant temp.
#################
7c - Footwell discharge temp.
8c - Sun sensor (dash top)
9c - Sun sensor.
10c - Passenger compartment fan speed.
11c - Passenger compartment fan voltage.
12c - Temperature mix Flap command 1=COLD, 100=HOT
13c - Temperature mix Flap position
14c - Central Flap command
15c - Central Flap position
16c - Footwell/Defrost Flap command
17c - Footwell/Defrost Flap position
18c - Recirculation Valve command 1=OFF, 100=RECIRC
19c - Recirculation Valve position (feedback)
20c - Vehicle speed in kph, updating only once per second. (real speed, not speed+safety margin as in the speedometer)
21c - Engine RPM in hundreds. This too only updates once per second.
22c - ?
23c - ?
24c - Sun sensor, exterior lights switch & panel lights control (term. 58 & 58d voltage) - used for A/C panel display illum.
25c - ?
26c - ?
27c - ?
28c - Fan speed?
29c - ?
30c - Engine run time in seconds (255 max.)(=0xff)
31c - Timing counter
32c - Displays test
33c - Software version? Mine states 3.4
34c - ?
35c - Outside temp. from inlet sensor (filtered?)
36c - temp?

If both fans remain off if the coolant temp climbs to above 212F and higher then obviously that's a real problem. And it would appear to be a single point failure. My WAG would be the temperature signal is not getting to the DME or is getting to the DME but does not reflect reality.

Using the above method to view the coolant temperature might highlight this.

I have not actually seen a real temp reading, the gage gets to the 0 on the 180 and doesn't kick on, i will try what your suggesting to do, thanks for your help, i am trying to sell the car and don't want to sell it if there is a problem, fix then sell lol

ok i tried that and it went up to 215 and didn't kick on the fans, had to turn ac on

These are used to run the fans at slow speed.

I've had to replace at least one on my Boxster. I had the tech replace the fan and motor assembly.

The resistors can take a beating. Often what I'm told the techs find is if anyone had been in this area the ballast resistors are not mounted properly but just shoved/jammed between some plastic panels. The resistors need to be properly secured so they do not run too hot and are not subjected to water splash which can damage them. Even if they are mounted correctly they can go bad over time.

If there is a way to salvage the radiator fan motor and reuse this (or in your car's case both of these) by replacing just the resistors I'm sure someone has done this and written about it. Otherwise you are probably looking at replacing both radiator fan motor assemblies. I seem to recall the cost of one of these was not that much higher than the cost of the resistor so if this is still true (assuming my memory is right about this) then with new radiator fan assemblies you get not only new resistors but new fan motors as well.

(My Boxster has been through one and my Turbo has had both radiator fan motors replaced. One due to a broken shaft, the other side because while the fan was running it was not moving nearly as much air and was using way more current than the other side.)

but it is in a forum to which I do not belong or no longer remember/have a user name/password to access. I think the link at this forum actually references a write up on Pedro's Garage site, so you might just go there and see if you can find the write up.

[pedrosboard.com]