My heater is not blowing hot air? - 1994 Toyota Previa

SOURCE: air condition/heater

sounds like the air-conditioning expansion valve is probably not working correctly here is a way you can fix your air conditioning:

1. Realize that auto AC is basically a refrigerator in a weird layout. It's designed to move heat from one place (the inside of your car) to some other place (the outdoors). While a complete discussion of every specific model and component is well outside the scope of this article, this should give you a start on figuring out what the problem might be and either fixing it yourself or talking intelligently to someone you can pay to fix it.

1. Become familiar with the major components to auto air conditioning:
   
   
2. the compressor, which compresses and circulates the refrigerant in the system

• the refrigerant, (on modern cars, usually a substance called R-134a older cars have r-12 freon which is becoming increasingly more expensive and hard to find, and also requires a license to handle) which carries the heat
• the condenser, which changes the phase of the refrigerant and expels heat removed from the car
• the expansion valve (or orifice tube in some vehicles), which is somewhat of a nozzle and functions to similtaneously drop the pressure of the refrigerant liquid, meter its flow, and atomize it
• the evaporator, which transfers heat to the refrigerant from the air blown across it, cooling your car
• the receiver/dryer, which functions as a filter for the refrigerant/oil, removing moisture and other contaminants

1. Understand the air conditioning process: The compressor puts the refrigerant under pressure and sends it to the condensing coils. In your car, these coils are generally in front of the radiator. Compressing a gas makes it quite hot. In the condenser, this added heat and the heat the refrigerant picked up in the evaporator is expelled to the air flowing across it from outside the car. When the refrigerant is cooled to its saturation temperature, it will change phase from a gas back into a liquid (this gives off a bundle of heat known as the "latent heat of vaporization"). The liquid then passes through the expansion valve to the evaporator, the coils inside of your car, where it loses pressure that was added to it in the compressor. This causes some of the liquid to change to a low-pressure gas as it cools the remaining liquid. This two-phase mixture enters the evaporator, and the liquid portion of the refrigerant absorbs the heat from the air across the coil and evaporates. Your car's blower circulates air across the cold evaporator and into the interior. The refrigerant goes back through the cycle again and again.
2. Check to see if all the R-134a leaks out (meaning there's nothing in the loop to carry away heat). Leaks are easy to spot but not easy to fix without pulling things apart. Most auto-supply stores carry a fluorescent dye that can be added to the system to check for leaks, and it will have instructions for use on the can. If there's a bad enough leak, the system will have no pressure in it at all. Find one of the valve-stem-looking things and CAREFULLY (eye protection recommended) poke a pen in there to try to valve off pressure, and if there IS none, that's the problem.
3. Make sure the compressor is turning. Start the car, turn on the AC and look under the hood. The AC compressor is generally a pumplike thing off to one side with large rubber and steel hoses going to it. It will not have a filler cap on it, but will often have one or two things that look like the valve stems on a bike tire. The pulley on the front of the compressor exists as an outer pulley and an inner hub which turns when an electric clutch is engaged. If the AC is on and the blower is on, but the center of the pulley is not turning, then the compressor's clutch is not engaging. This could be a bad fuse, a wiring problem, a broken AC switch in your dash, or the system could be low on refrigerant (most systems have a low-pressure safety cutout that will disable the compressor if there isn't enough refrigerant in the system).
4. Look for other things that can go wrong: bad switches, bad fuses, broken wires, broken fan belt (preventing the pump from turning), or seal failure inside the compressor.
5. Feel for any cooling at all. If the system cools, but not much, it could just be low pressure, and you can top up the refrigerant. Most auto-supply stores will have a kit to refill a system, and it will come with instructions. Do not overfill! Adding more than the recommended amount of refrigerant will NOT improve performance but actually will decrease performance. In fact, the more expensive automated equipment found at nicer shops actually monitors cooling performance real-time as it adds refrigerant, and when the performance begins to decrease it removes refrigerant until the performance peaks again.

SOURCE: heater blows only cooled air

my heater only blows cold air please could you give me some advice on this thanks . everything else is ok temp ,engine etc

SOURCE: 93 gmc sierra heater not working

THERMOSTAT REPLACE IF NOT SEE IF HOSES ARE CLOGGED SHOT OF AIR COULD HELP OR DISSCONNECT BATTERY CABLE 10-15 MIN CONNECT BACK TRY HEATER

Paul W

• 404 Answers
• Posted on Mar 01, 2009

SOURCE: heater only blows cold air but hoses are hot

Hi!
It appears we have an Air lock scenario and you will need to perform a system Bleed.
Park the vehicle on level ground, when cold remove coolant filler cap, start engine and leave to idle, turn heater on full and blower to max. When engine reaches operating temperature watch and listen near coolant filler, keep clear as gurgling and hopefully a boil over should occur. Top up with very warm coolant and wait as it may do it again.
Check for heat inside vehicle if warm replace coolant cap but keep an eye on temperature gauge as the ~Air lock may have moved on from heater matrix/core so proceedure needs to be carried out again from COLD.
If persistent boil ups/over attention must made in the cylinder head
or gasket area, or possibly water pump?
Please press the Blue button to appraise my FREE Efforts, Thank You!
Paul 'W' U.K

SOURCE: Why doesn't the heater blow hot air?

If your "Check Engine" or "Service Engine Soon" light is on, you need to have that checked out first.
If not, the next thing you should check is your engine coolant level. (Antifreeze) If the coolant level is low, the engine coolant does not circulate through the heater core and the the heater doesn't work. The coolant level could be low for a number of reasons including a leaky hose, water pump, or head gasket. In any case, if it is found to be low, you need to find out why.
If the coolant level is OK then the thermostat function needs to be checked to make sure that the engine is reaching operating temperature.
If all of the above checks out OK, then the heater control valve and/or the blend air door in the HVAC housing needs to be checked for proper operation. (NOTE: some cars are not equipped with a heater control valve)