Chevrolet Repair: heater blower only runs on high, chevy s10 pickup, resistor pack

Question
hi i have a 88 chevy s10 pickup. 2.8 w/air . my poblem is the heater blower only blows on high. i already replaced the resistor and switch assembly.im not sure how to trouble shoot the wiring to see if there is power at the switch for the lower speeds. can u help me in how to test the switch and the resistor harness's to see if the problem is in the wiring..i assume that the blower motor is ok, being it runs on high.also i notice when i switch it to high the headlights dim abit momentarily  any help will be appreciated. thanks, john miller


Answer
Hi John,
That symptom is almost always the resistor pack.
The motor is good.
There is also power to the switch, or it wouldn't work on hi.
The best place to test the switch operation is at the resistor pack connector. At different speed selections of the switch, different wires in the connector should be hot. Have the connector unhooked from the resistor pack.
Go here, and scroll down to fig 15.
http://www.autozone.com/az/cds/en_us/0900823d/80/12/41/a3/0900823d801241a3/repai...

It is possible the relay is not making contact when not in Hi, so swapping relays would help eliminate that.

Van