1996 Chevy caprice classic 5.7L. My cooling fans won't turn on when engine gets hot, the vehicle isn't overheating. The AC blows hot air. The 25 fuse for air under the hood was replaced twice burns out and the connector to the cooling fan has a burnt area as well. What could be the problem? Radiator has been replaced and the thermostat.

It sounds like your AC unit could be overheating or even damaged.

AC units have a sensor that will turn them off automatically to prevent damage from overheating. If there is an insufficient amount of air flow, the unit will heat up, and then eventually turn off.

When the car is moving, more air is forced over the unit, likely keeping it cool enough to run, however, when the car come to a stop, it loses that air flow, and quickly heats up. Thus, the AC would work while the vehicle is in motion, and overheat and stop when the car is stopped and idling.

However, the AC unit could be completely blown. The cold air while moving could be just a case of air being forced into the car. Think of a house fan, the fast the wind blows on you, the cooler it gets.... Thus, it could be an illusion that the AC is working when car is in motion, when it really isn't.

Hope this helps.

Most common low on freon,or the low pressure cycling switch,If its beacuse its low you should fix the leak and refill.

CHECK TO SEE IF COOLING FAN IS RUNNING.IF NO CHECK COOLING FAN FUSE AND RELAY.THE COOLING FAN NEED TO BE RUNNING WHEN AC ON BECAUSE AIR CONDITIONER PUT A LOAD ON ENGINE.COOLING FAN KEEP RADIATOR AND AC CONDENSOR COOL.FAN NEED TO RUNNING.

Air conditioning is one area where the owner generally is not qualified or equipped to perform the necessary repairs. If you are overheating and the ac isn't cooling I would check the condenser (radiator in front of the engine radiator) and made sure it's not obstructed. Also make sure that the electric fan comes on when you engage the A/C. Beyond that there isn't much you really can do except have an professional run a diagnostics on the system.

Does the engine appear to be overheating? Signs of engine overheating are :
1. Sluggish engine operation when hot.
2. Detonation upon acceleration (pinging).
3. Coolant boiling in overflow tank.
If any of these symptoms are present, then place a cooking thermometer on the upper radiator hose where it connects to the engine. Tape the thermometer to the hose to hold it in place. Run the engine until operating temperature is reached. The temperature should stay between approx. 195deg.F and 225deg.F. If it goes over 230deg.F, then overheating is indicated. Before shutting off the engine, check to see if the engine cooling fan is running. If not, then turn on the AC switch and see if it comes on. If the fan still does not turn on, then a faulty cooling fan or fan circuit is indicated. Other causes of hard/no start when hot include :
1. Dirty air filter.
2. Bad temperature sensor (computer).
3. Bad map sensor.
4. Bad EGR valve.
5. Failing ignition module.
6. Leaking injector(s)
If the vehicle is used primarily as a work vehicle, then it might be overdue for an oil change.
If the oil is fuel soaked, then it can cause an over rich mixture during hot restart.
I hope that this information is helpful and thank you for using Fixya.com.
CAUTION : Be careful when working around a running engine. Keep hands and loose clothing away from moving engine parts and engine cooling fan.

Your cooling fan relays are controlled by the Engine Control Module (ECM). What you are unplugging is probably the Engine Coolant Temperature Sensor (ECT). The ECM will default to "fans on" if it loses the circuit to the ECT. (It loses it when you unplug it) This is why the fans come on when you unplug the connector. The engine might be overheating because the ECT may be malfunctioning and "lying" to the computer about what the actual engine temperature is. If this is the case, the ECM is not turning the fans on because it doesn't "think" it is hot enough to need them. Then again, you could have a faulty temperature gauge that is making you think the engine is overheating when it is not. (If it is boiling over, then it is OBVIOUSLY overheating and you can just disregard that last statement.)
Anyway, the only way to properly diagnose the cooling system on your vehicle is to access the live engine data and look to see what temperature the ECM is seing while you take an actual reading with an infrared thermometer or a pyrometer and compare the two. Yhe thermometer or prometer reading should be within about 5 degrees of what the ECM "thinks" the temperature is. If there is a larger error than this then the coolant temp sensor should be replaced. If the reading is within this range and the temperatur gauge reads hot when it is not, then the gauge should be replaced.
Since the fans come on when you unplug the sensor, you know that all the fan circuits are working and the ECM is capable of controlling them, so it almost has to be a computer INPUT problem, not an OUTPUT problem.

Hello and welcome to FixYa! If you have overheating problem, it can lead to multipleissues. You may be running on low coolant that's why the vehicle overheats. Ifthat's the case, please add coolant and make sure that it sits on the rightlevel, too much coolant can cause overheating too for coolant will overflow. The vehicle may have a faulty or worn out radiator blowermotor that's why it overheats. If that's the case then you will need a blowermotor replacement to resolve the issue. If the radiator is clogged with dirt and rusts this issueoccurs too. The coolant doesn't flow normally on the cooling system if it'sclogged. If that's the case, I strongly suggest that you have the radiatorflushed to drain out dirt and rusts. If you think that the radiator served youenough then it's better to have it replaced. Please do check the radiator hoses, If you have worn outhoses it can cause coolant leakage which can result to overheating. A tiny holeis good enough for the vehicle to overheat. A faulty thermostat sensor can cause the issue too. If youhave worn out thermostat, the fan may not trigger that's why the fan won't workwhen under stressed conditions. A blown radiator blower fuse can cause thisissue too so I suggest that you check the radiator blower fuse and replace itwhen necessary. What causes the radiator blower fan fuse to blow? It's becauseof a failing radiator blower motor, If that's the case have the radiator blowerfan motor replaced. If the fluid in radiator doesn't circulate then it meansthat you have a blown head gasket or a faulty water pump. I suggest that you gofor the water pump replacement first specially if you think that it's near theend of it's service life. Usually, water pops out the radiator when engine isreved (a sign of faulty water pump and possible blown head gasket). Hope you find this information helpful enough and thank youfor using FixYa! Have a good one!

WHEN CAR STARTING OVERHEATING MAKE SURE COOLANT LEVEL DIDNT GET TOO LOW. IF NOT I WOULD REPLACE THERMOSTAT AND RADIATOR PRESSURE CAP IF OVERHEATING WHILE SITTING IDLING COOLING FAN NOT COMING ON.CHECK COOLING FAN FUSE AND RELAY IF ALL IS GOOD.CHECK COOLING BY HOTWIRING IT.IF RUNS YOU HAVE A BAD COOLANT TEMPERATURE SENSOR OR FAULT IN WIRE CIRCUIT.IF FAN DONT RUN WHEN HOTWIRED REPLACE FAN MOTOR.IF CAR STILL KEEP OVERHEATING CHECK ENGINE OIL LOOKS LIKE MILK BLOWN HEAD GASKET.IF OIL LOOKS OKAY YOU NEED RADIATOR AND ENGINE FLUSHED OUT.

check the radiator. maybe you punctured it.

your AC cooling fan is not working properly, most vehicle has two fans, one for the radiator and another for AC, both work in sync with one another; if one cooling fan only working it does not produce enough cooling for both radiator and condenser at the same time; by running ac you producing more heat and its cant cool the engine fast enough with one fan so your engine is overheating when running AC. The temperature sensor could be faulty and need to be replace or your fan motor can also be faulty. Check the fuse first and the relay make sure they are not burn out. sensor cost about 30 bucks get it new, relay 35-40 new used 5 bucks at junk yard, fan get it from a junk yard for 25-30 bucks, new will run over 100 bucks. don't run the air and overheat your motor, it can damage your engine or may blow your radiator. if you do run ac watch the temp very closely, don't let temperature get into the red.