I have had the rad and heater core flushed. The operating temp does reach normal but not quite as quickly as I would like (will change thermostat sometime soon). The problem is lack of consistent heat. While driving the heater can blow hot but then for no explained reason start blowing cool while operating temp stays normal. I find that if I play with the heater control **** (turning between cool and hot) this can cause at times to blow hot again!!?? I have run the car with the cap off to remove any air locks. Any ideas would dearly be appreciated.

thanks!

 

Do you have air conditioning? combination A/C-heat control vacuum switches and vacuum lines are prone to failure. Start by checking for a cut or damaged line first (usually makes a faint hissing ir sucking sound). You may also hear noise coming from the area of the switchinstead - that would help center you on the switch in that case. At any rate it seems like your heater selector (whether vacuum or cable operated) would be the place to start searching.

 

thanks goinstrong Yeah I do have AC. Are these vacum lines easy to locate (obvious)?

 

Yes - especially if you have a small mirror. Just trace them right off the switch. Look for color tracers (stripes) on the line to identify each one. Look for any obvious noises while the car's running. Some systems use a lot of lines. Sometimes you must also remove and separate them from the wiring harnes (the companies like to tape them together with electrical tape in a bundle). You can remove the electrical tape and any plastic (usually black in color with a split on one side) shroud to trace them more easily. Be somewhat careful if removing tape not to cut a wire or vacuum line if using a tool like a razor blade or sharp scissors. If you have plastic vacuum lines be extra careful not to bend or kink them. They also fail by age/heat cracking quite easy if plastic - so pay special attention to them in this case. They usually connect with a rubber end evev if plastic - sometimes the rubber cracks with age/heat also.

 

Look up under the middle of the dash and see if you can find the blend door actuator. The symptoms you sescribe sound like it is either the actuator going bad or a bad connection somewhere. Here is a diagram of the part.