The SDL doesn't have a relay.

It has a "blower controller", a very costly part that regulates the blower speeds. If the blower functions with 12V applied directly, the problem is either the CCU or the controller.

However, intermittent blower operation can also be attributed to a worn ignition switch............the symptoms are similar. If you get high blower speed on occasion............and then nothing...........I'd work with the switch to see if you can affect the blower operation...........and then you'll know it's the culprit.