Fan for heat turns on and off and sometimes stays off

The most common cause of this problem is that the drivers seat heater grid is open or burned out. That is based on 25 years as a Ford dealer technician.

Sounds like the blower control module. Alo inpect the multi wire plug,they sometimes get damaged from the heat. The module and plug should be in the immediate vicinity of the blower motor,generally behind or below the glove box

check your fan relays and temp sending units...turning on the heat will help dissipate heat from coolant. turning on a/c will engage secondary cooling fan...check your relays and sending units

I would disconnect the fan connector and use contact cleaner to clean the connection. Usually corrosion. Also fan might be going bad (Common Problem).

Could be the second fan motor or a relay. Have the circuit tested for the second fan.

check radiator fan motor first, if good check fan belts. then check thermostat. also check radiator for blockage.

Most modern vehicles using an electric cooling fan have a thermostatic switch that will allow them to run even after the engine is turned off. Start and stop driving can cause heat buildup in the block which can cause problems such as the one you have and if the fan isn't bringing the excessive heat down during a stop, the hot engine can refuse to idle or accept fuel as it should.
You should listen to see if the fan is turning on after the ignition is off; this is sometimes delayed for a minute or so until the thermostatic switch adjusts to the rising block temperature and starts the fan. If the main fan is belt-driven, it may be the AC fan that is used for this purpose.

cOOLING fAN tURNS ON @ 210-230 dEG. tEMP sENSOR bAD & OR fAN relay cAN cAUSE THIS pROBLEM

Older cars sometimes have many difficult problems, especially the wires problem, it is very hard to find out which wire got trouble, I think your Olds wire got hot sometimes before and some wires connected together and by pass.

Olds is GMC products, the plastic sucks easy to melt, sometimes also cause the engine over heat, because the cooling fan doesn’t work right.

Good luck, my friend.

Frank

Check the fan's resistor (behind the glove box) and its connections to the fan and power source! You can easily do this yourself.

My 03 Civic LX (sedan) was doing the same thing ~6 mos. ago (no fan, a/c wasn't clicking on/off, nuthin). The dealer SWORE (almost with his job) that it was one or both of the 2 control boards in the dash (one has 3 potentiometers aka variable resistors, the other has 3 on/off contact switches) and would cost ~$200 each.

It turns out that both were good, and the culprit was the fan's resistor (~$60) had burnt up. I would first check the fan and its resistor for a loose connection before bringing it to a mechanic.

Open the glove box, remove 2 pins on either side of the glove box, then let it hang fully open. On my sedan I had to remove the a/c filter box to get to the fan.

Good luck!