98 riviera climate control

Does anyone know what would cause the heater fan motor to run intermittantly?
Some times will go for weeks without a problem and then will decide to not blow at all. When it starts up again, maybe an hour later or so, it will run up & down by itself betwwen low & medium speed & will either stop running or go to the desired blower setting as if there was nothing wrong.
This symptom appears quit randomly and is not dependant upon outside temperature. It has happenned at 90 deg. F & -20 deg F.
Thanks for any ideas.

Fixed it. It was the heater control module!

Fixed it. It was the heater control module!
How did you decide to replace the module?

When I went to remove it for testing, the blower would start up & stop, depending on pressure applied to the module, indicating an electrical fault within the module. Gerryt www.used-tractors.ca

When I went to remove it for testing, the blower would start up & stop, depending on pressure applied to the module, indicating an electrical fault within the module. Gerryt www.used-tractors.ca
Was this the rectangular module that fits into the duct beside the blower motor? It has two plugs. One with a single red wire and one with a purple, black, and gray (black stripe) wire.

You got it!
2 screws to take it out at the bottom