[Rober104]

1990 mustang gt v1 vortech, heat has never worked and its been bad recently and I looked to fix the heat.. ac has been deleted. When trying the heat it will come on for say maybe 10 seconds, then it'll go off. Little while later it will come back on for say maybe 2 seconds and go back off and then repeat... while driving the rpm needle acts crazy like there's a loose wire when it turns on for those 2 seconds, Replaced the blower motor resistor and all 4 of the modes work now but it still does the same exact thing..
I've been suspecting maybe a loose ground and going to check when it gets a little warmer hopefully sooner than later but wanted to see if anyone had this problem or possibly a solution

 

[Rober104]

If I run it on low then it runs with no problem and won't cut off, medium it will run longer but then cuts off, if you run it on high it does the 2 second cut off...

 

[Dwain]

Maybe the blower motor itself has an intermittent short that is dependant on it getting hot from being used. You can use a multimeter when its having the problem and see if the power is cutting out to the motor or if the ground is being lost by probing the back side of the connector. If its not losing power, i would replace the blower motor. If its losing power youll need to back trace the wiring and see where its losing signal. Is the tach bouncing really high at low rpm, or does it stop working then starts again?

 

[Rober104]

Going to check the blower motor here In a few, not trying to just throw parts at it before actually figuring out the cause.. looked before work and the fuse box #9 for the 30amp is melted and looks burnt. I'm thinking previous owner hard wired it to work as the resistor was bad and now all selections work for the fan. Works on low and doesn't cut out but on medium it cuts out but stays on longer and on high it cuts off after 2 seconds (figuring overload) as to also the heater core hoses are warm but still no hot air on the low setting.
Going to pull the motor today and see if I can get a correct reading and see if I can't find where the splice is and maybe correct it with an inline. Thank you very much for the reply and I'll keep this thread updated with what I find.