2002 Nissan Sentra Heater does not blow hot air and the temp indicator jumps high and low

yeah, low on coolant, or a blockage in the cooling system. I would do the thermostat first, should be simple and fairly inexpensive.

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Sounds like the heater - ac door actuator is not working. This part would need to be replaced, it's not repairable.

Heater core may be clogged. Try flushing it to see if water flows through freely. Also check the heater water control valve for restrictions.

Might try a reverse flush of the cooling system. Might reverse flush the heater core too.

Are you talking about the engine cooling system or a problem with your Auto A/C?

i assume u r refering to the cooling fans,,, if this is so the freon is low ,fans come on and lower the high side ,there fore lowering the low side and the low side switch cuts it off and on,,charge it up

If all of the things you replaced are working fine I am going to say double check the thermostat. Also make sure your fan is engaging at temp. You cam check by running till warm and then running the AC. If the car does not overheat with the AC on then your fan is not running under normal conditions (with AC off) This can be caused by a couple of different things depending on how the fan is set up. I am not a nissan expert

My 2005 Nissan Sentra 1.8s with 55,000 mi. blows cold air from the heater. Coolant not circulating in engine. Lower hose stays cool to touch. Both heater hoses cold. Changed thermostat - didn't fix it. Coolant not leaking or dirty. None in oil - no oil in radiator. Changed worn water pump belt - pump spins freely with no noise or resistance. Cooling fans come on after warm-up. Temperature gauge stays in normal range then jumps to hot and back again. Coolant good to 10 below - didn't freeze here yet. No other problems or repairs to car. Afraid to drive and make worse. Help!

My 05 sentra with 79k miles heat will warm up and then get cold after a mile of driving, we have tried to get the air pocket out, the mechanic stated he thought it could be a blown head gasket, another mechanic said it was a bad heater core. Any advice would be appreciated.