What do you mean by "has no heat"? No air blowing out, blowing out cold air when heater is on, blowing nothing at all? Heater not turning on? What specifically is happening?
it could be a couple of things you could have a bad thermostat or a bad heater core
One of the reasons a 2000 Jeep Cherokee heater would randomly blow cold air and then hot air and then cold might be that there is a problem with the hot/cold duct. The air or a vent might be inadvertently blowing periodically.
blend door is broken re-move dash and replace
this is not an answer just an update. coolant is filled
The HeaterTreater is an after market kit that solves heater and AC for the Jeep Grand Cherokee and Laredo. It is much cheaper than the dealership fix and is easy to install. For diagnosis and info, check out www.heatertreater.net or search eBay for "heatertreater".
The heater core is leaking. GEt a manual from DISCOUNTAUTOREPAIRMANUALS.COM and replace it.
Thermostat and/or heater core may be defective
Sounds like your cooling system termostate is stuck open.
The most common reason a automobile heater blows cold air is the water level is low. Check the water level and fill to the appropriate level.
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Because your jeep wrangler is over heating, you must have a sensor in the dash not working If that smoke is steam, the heater core is leaking and in need of replacement.