Interesting electrical issue, cooling fan relay powering A/C air blower relay?!

[ALEXtheGREAT]

1984 944, sorry for the long post.

So I've got this weird issue that I can't seem to figure out. Long story short my A/C wasn't working and I found the original A/C relay behind the glove box had failed, so I ordered a new OEM replacement from Porsche. Relay arrived and I figured I'd swap the cooling fan relay and A/C relays.

I placed the original working relay from the relay block to the A/C relay spot behind the glove box and inserted the brand new relay into position one of the fuse block. As soon as I went to insert the new relay, I heard the A/C air blower relay (position 3 on the fuse block) click and energize. Blower motor started running at its position "0" setting (as if ignition was on) and I could turn the A/C on without they key in the ignition. I was unable to get the radiator fans to stop running unless I removed the cooling fan relay completely.

I swapped both relays (brand new relay into the A/C relay position and original working relay back into its original cooling fan relay position on the fuse block). Upon inserting the original relay, I did not hear the A/C air blower relay click or energize, the blower fan no longer runs and I cannot turn the A/C on without the key in the ignition.

I figured maybe my new relay was defective so I had a new one ordered. Relay arrived and I again inserted the relay into position 1 on the relay block. As soon as I made contact with the board, the A/C air blower relay (again position 3 on the relay block) clicked and energized.

I cannot figure out why the brand new relay is causing the relay to energize and allow the blower motor and A/C to work without the key in the ignition, where the original relay isn't having these issues. Any suggestions!?

[walfreyydo]

I think we confirmed over on Rennlist that your new relay was bad, no? Failed the diode test?

[Monkey Wrench]

when you put the key in the ignition this is closing a set of contacts, much like turning the key to the second position in a " normal car."

I'd verify if that power wire is consistent as it might be intermittent, you seem to be having some different results. this wire probably turns on power to some of the fuses in your fusebox. Id note which fuses are energised with the key out as opposed to the key being present. write them down for your reference.

if you think you are blowing up relays and cant; decide why , there is no harm in inserting a in line fuse or just making one up from a couple hunks of wire and a fuse that's appropriate for the draw, maybe one with connectors not like the little porcelain europen ones..

It sounds like it could be a case where a short perhaps something similar is blowing relays by overloading them. you might check current draw or maybe the resistance through the motor if its running a motor. you may not know that the motor's resistance is but it probably wouldn't' be 0 ( a Dead short) if the motor is physically stuck maybe it can draw way more than normal. try turning the motor physically..


if you wire in some fuses temporarily and then see the fuses blow than its a clue.. fuses are cheaper than relays , usually.


some multiple speed motors have separate windings that can be switched in or combined, to change speeds.

sometimes motors just have 2 wires and resistors are used to slow the motor by wasting power, by making heat basically.. the motor may run at 12 V full speed but be reduced in voltage by a voltage drop through a resistor in the same circuit. for example a 3 speed motor may see 8 10 and 12 volts depending how much resistance is added to the circuit. this is not uncommon for heater / AC fans or rad fans. if one resistor blows or breaks, and it is in circuit with the motor, then it will be open circuit and no rotation. in other words power cant; get through an open resistor to run the motor if the resistor is in the same circuit as the motor.