Originally Posted by Alan

That is just the fuse tester - it has nothing to do with the relay part - its just a way to test fuses.

Either DEF mode & DEF relay or the blower Switch on high should make the blower run - both require the Blower Relay to turn on and Fuse #17 (HVAC Blower) must be good. Since neither works - I'd not waste any time on the DEF relay.

You need to do the tests Wally proposed to test the blower relay function. The small relay in the head unit can cause the AC not to work - but it doesn't cause the blower not to work... so deferr testing that.

In addition to what Wally proposed, assuming adding the blower relay bridge between 87/30 makes the blower run - then with the blower relay out - test pin 86 on the socket - it should go to 12v+ when the car is running with HVAC head connected and not in the "Off" mode. If this doesen't happen - you need to know why? this is the root of your issue..

BTW - are you sure you are removing & testing the right relays ...?? The labelling is not systematic wrt position - you must pay attention to the little arrows by the labels.... Lot of people didn't get this...

Alan

Originally Posted by WallyP

1) Pull Relay X, the Blower Relay. Look at the diagram on the side, and locate Terminal 30 in the relay socket. Use a test light to check for power on Terminal 30 - there must be full battery voltage. If so, go to 2). If not, the fuse contacts on Fuse 17 are probably faulty.
2) If you have power on Terminal 30 of Relay X, install a temporary jumper between Terminals 30 and 87 in the socket for Relay X. Try the blower switch. If the blower works normally, the Resistor Pack is OK. If the blower works only on the highest speed setting, there is a broken resistor wire in the Resistor Pack. If the blower doesn't work at all, there is a faulty connection somewhere between Terminal 87 and the blower motor.
3) If the blower works at all, remove the relay jumper and install Relay X in the socket and repeat the test. If the blower works exactly the same with the relay as it did with the jumper, you should now know what the problem is. If the blower does not work at all with the relay installed, swap Relay X and Relay VIII (the Defrost Relay). If the system still does not work, you probably have a failure in the HVAC Control Unit or elsewhere. The most common failure is the small relay inside the unit. This can be replaced.

It is possible that you have a problem with the cabin air temp sensor - perhaps the fan motor - but do the suggested tests first.

Originally Posted by cgraner

What year model are these instructions for? I have a similar problem with a 1979 Porsche 928. The fuse/relay panel is different than what you call out on these instructions. On a 1979 the HVAC Blower relay is XXI 21 and the DEF (Front) is XXII 22. Are the relay pinouts for jumpering going to be the same?

https://928srus.com/pages/charts

https://cdn.shopify.com/s/files/1/16.../1977-1979.png