Blower Regulator part number???
 

I have a 99 C230 kompressor. The problem:

The fan for the heating and AC works ok sometimes, but will then suddenly go crazy. When this happens I am unable to control the speed of the fan with the switch unless I turn it off.

I looked at other posts and I rekon this is due to a faulty heater blower regulator. My questions are:

1. Can I test this item now I've pulled it off the car, or do I just have to order a new one and hope its the culprit?
2. There are two Behr parts listed on all the supplier websites for this item. They are "Blower Regulator R2022-110518" and "Blower Regulator Heater : A/C R2022-128594". Which one do I need?

I know the mercedes part no is 202-820-73-10, but this doesn't tell me which part I need.

Any advice?

regards

chuck