Having problems with your 1991 Ford F150 ?
1999 ford f150 heater no blowing any heat - 1991 Ford F150
Sounds like the thermostat is stuck open and needs to be replaced. That would be the first place to look. If all teh hoses are not hot, that would be a good indicator.
Repair Help & Product Troubleshooting for 1991 Ford F150
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