I just had the brake fluid and oil changed in my 2002 F-150 at a chain oil and lube shop. Now, my heater a/c fan doesn't respond to the switch. It comes on and goes off intermittently. I am thinking it is responding to changes in engine vacuum as I accelerate and brake. Did the lube guys break something?

2002 F-150. I had the oil and brake fluid changed at a chain shop. After, I now have a
problem that did not exist before. The fan for heater and a/c does not respond to the
switch. If the fan is on max, it blows full on then stops, then will blow full on. If the fan
is set at a lower speed, it does the same, blows, then stops, then blows, then stops. I
am associating the change with changes in engine vacuum as I accelerate or let off
the gas and/or brake.  I replaced the control head for a/c, heater, fan just over a year
ago at a Ford dealer so I know the control unit is good.