Question about 1999 Chevrolet Blazer

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My 98 S10 BLAZER'S heat does not work.

The coolant level is good. The engine runs at a normal operating temp. The blower runs at all speeds. Zero heat. I suspect the actuator valve but I'm not sure where its' at.

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  • Roberta Smith
    Roberta Smith May 11, 2010

    feel the inlet and outlet hoses to the heater core... are they both hot ?



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The most common reason for no heat is a faulty thermostat. this is an easy and cheap fix also. go to an autozone store and they will assist you in changing it.

Posted on Feb 17, 2009


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2003 grand marquis no heat engine temp normal other eatc ops all normal. is there an external heater control valve on the car?

  • Insufficient, erratic, or no heat
  • Low engine coolant level.
  • Engine overheating.
  • Plugged or partially plugged heater core (18476).
  • Temperature blend door binding/stuck.
  • Temperature blend door actuator (19E616).
  • Incorrect heater control valve (18495) operation.
  • Go To Pinpoint Test I .

Are the heater hose's going through the fire wall hot ?
I2 CHECK FOR HOT WATER TO THE HEATER CORE INLET HOSE WARNING: The heater core inlet hose will become too hot to handle and may cause serious burns if the system is working correctly. Allow the engine to reach normal operating temperature. Feel the heater core inlet hose.
  • Is the heater core inlet hose too hot to handle?
Yes GO to I4 .

No REFER to Section 303-03 to check cooling system function.

Jan 06, 2018 | 2003 Mercury Grand Marquis


Over heating

Cold engine - - check that coolant level is correct - Ignition on but engine not running - set heter temp settings to max - set fan manual to one of the lower speeds - start engine and within 30 seconds rev it 3-4 times up to 3000rpm - shut off engine before end of 30 seconds (before it starts to heat) - reset climate to normal settings - recheck coolant and top up if necessary. Hot engine. - take car for a run to get up to operating temp - using caution - slowly open the bleed valve (steam and bubbles may come out) - close as soon as you see liquid coolant without excessive bubbles. - do not overtighten this as they are plastic threads. Just snug till it seals fully. - after engine cools check the coolant level again and top up if necessary. Check coolant level every few days for a few weeks and top up again if required - repeat the Hot engine bleed process again. If coolant keeps droping after 2-3 top ups have the system pressure tested. If you are still getting over temps have it analysed by a dealer. The temp is controlled by the engine computer so there may be another fault.

on May 19, 2008 | 2006 BMW 545i

3 Answers

1999 ford expedition , runs good doesn't overheat , but puts out no heat ?

heater core might need replaced . check the hoses going to it under the hood after it gets to operating temperature .One should be hot and the other not so much

Nov 19, 2015 | Ford Cars & Trucks

2 Answers

My 2005 gmc seria heater will not blow hot air

There are a number of possibilities.
First, its the level of coolant in the radiator full?
Low coolant level will cause this, because the heater is higher than the engine, so air can rise to the heater and form an air-lock.
Second, is the thermostat good?
A thermostat that is stuck open will not make heat for the heater.
Third, the control valve may be stuck or broken, not allowing the hot water to flow to the heater core.
Usually these are vacuum operated, and usually found under the hood.
God bless your efforts.

Oct 26, 2015 | GMC Cars & Trucks

1 Answer

How do i flush the heater core on the 2007 ford tarus

you may have air in coolant system you should have a bleeding point somewhere and good idea to change pressure cab too.
Just becarefull engine coolant and heating system is a pressurized system that works on high temp. can cause a serious injuries!!Safety.
you need to run the car on idle with heat on at high speed and open and close the bleeding valve with proper size and long reach tool
till no air bubbles comeout make sure you run the car enough that thermostat opened and engine run on normal operation temp. for a while.good luck.

Dec 06, 2012 | Cars & Trucks

1 Answer

Heat sometimes works in 2003 envoy

First I recommend checking that your coolant level is good. Please check this cold so you don't risk getting burned. I have seen too many heater complaints where the coolant level was simply too low to fill the heater core. Next, you should check if the heater control valve is operating. I don't have any GM experience, but heater valves are often the cause of intermittent heater operation in many cars. Good luck!

Dec 20, 2011 | 2003 GMC Envoy

2 Answers

Heater only blows cod air even when engine is warm. changed thermostat. doesnt fog up ad smell like haeter core.

Your car's heater is a life saver in cold weather. Before attempting to repair your car heater, you should understand how your heater system works. First, on this page is an explanation of how the car heater system functions, further down the page are some pointers on heater system trouble-shooting. To warm the passenger cabin of your car, the heating system makes use of excess heat from the engine internal combustion process. A car's engine, in fact, when in operation produces so much excess heat that if the excess heat is not removed, it would destroy the engine. It is your car's cooling system that removes that dangerous excess heat. Some of the excess heat is released through the exhaust. Most of the excess heat is absorbed by a circulating liquid coolant, which is a mix of water and antifreeze. The heated liquid coolant is carried from the engine through hoses to the radiator, which transfers the heat from the coolant to the outside air. That heat transfer lowers the temperature of the liquid coolant, which is then circulated back to the engine to absorb excess heat again. Whereas the radiator is located at the car front grill, the unit that transfers heat to the passenger cabin is located inside the dashboard. This unit is something of a mini-radiator and is referred to as the heater core. Heated liquid coolant circulates through tubes in the heater core and a heater fan blowing across those tubes, as well as through little fins encasing the tubes, directs warm air through heating vents into the passenger cabin. Because your car's heating system works off of its cooling system, heating system malfunctions are often caused by problems in the cooling system. The heater core in your car is similar to the radiator in the front of your car; in fact it looks like a small radiator. The difference is the heater is mounted inside the car and air is blown through the fins of the core. The heater hoses transfer engine coolant from the engine to the heater core, this allows the heat from the engine coolant to be utilized and warm the passenger compartment. When a heater stops functioning determine what type of failure has occurred to execute a repair. We have listed the most common problems below:
Heater Core
Troubleshooting Procedure
  • Step 1: Check Engine Coolant Level - Most cars have coolant reservoirs with opaque white plastic tanks and measuring lines allowing you to see if the coolant is at the recommended level. Coolant expands when heated, and for that reason, most coolant reservoirs have a Full-Cold and a Full-Hot line. If there is too little coolant in the reservoir, you should be alerted to the possibility that there could be a leak somewhere in your car's cooling system. Remove the reservoir cap and add coolant to the Full-Cold line, if a very short time after you refill the coolant reservoir the coolant level is low, there is a leak in your car's cooling system. Engine coolant is used to heat the heater core and if the vehicle is low on coolant the heater core will stop working. The heater cannot produce heat due to the lack of heat from the engine coolant. Even if the engine is not over heating the coolant level can still be low. Inspect the engine coolant level in the coolant reservoir tank; coolant level should be between the hot and cold marks. Always check the coolant level when the vehicle is cold, preferably over night. Check for engine coolant leaks and repair as needed, then refill with coolant and recheck the system.
    Radiator Cap
  • Step 2: Inspect Heater Control Valve - The heater control valve is used to shut off hot coolant from entering the core when the heater is in the off position. A heater control valve can be actuated by either a vacuum line or a cable from the vacuum heater control valve to the heater core. This hose should be warm; if not the heater control valve is stuck and needs to be replaced. After the repair has been made refill the coolant level and recheck system.
    Heater Control Valve
  • Step 3: Check Vacuum Feed - Most heater systems are operated by engine vacuum. This vacuum is used to actuate servos to move the temperature adjustment doors inside the heater plenum. If engine vacuum is not present the heater will not operate properly. To test for this condition remove the vacuum feed line from one of the vacuum servos. With the vacuum feed line removed insert a vacuum test gauge. If no vacuum is present, open the hood and inspect all small vacuum lines from the engine to the firewall and repair as needed. If a hissing noise is present under the dash when the engine is running a vacuum leak exists and must be repaired to restore heater function.
  • Trouble Shoot Heater/Air Conditioner Blower Motor. An electrical motor is used to push air through the heater and air conditioner system. If this electric motor fails it will not force air through the system. Ground a test light lead to a good ground source, like a metal brace under the dash, seat mount bolt or under hood brace. Turn the key to the on position; check the fuse in the heater or blower motor fuse panel with a test light. Then lightly touch the service port at the top of the fuse on both sides. If the test light illuminates on both sides of the fuse, the fuse is ok and working properly. If the fuse lights the test light on one side it is blown and needs to be replaced. fuse_panel.jpg
    Power Distribution Center
    If you are unsure of the location of the heater fuse consult a repair manual. If the fuse condition is ok, position the blower speed to the highest setting. Connect the ground end of the test light to a known ground source. Then probe both ground and power feed wires of the fan motor. The test light should illuminate on only one of the wires (fan motor failed). If the test light illuminates on both wires the ground source has shorted. If neither of the wires illuminate the power source is shorted. To trouble shoot this style of problem a wiring schematic is needed.

Jan 12, 2011 | 2001 Chevrolet S-10

1 Answer

Does not.over heat runs great blower blows fine, fan speed switch is only runs on high but every now.and again it'll blow heat then strait back to cold. The temp on the car.stays perfectly...

First the switch this may not be bad switch it sounds like a bad blower resistor, this is what controls the speeds, the loss of heat may be low coolant level or a bad blend door actuator, depending on the heat/ac system in the van it may also be a bad vacuum leak in the engine compartment, some models use actuators to control system and some use vacuum, if the system looses vacuum the door will close until vacuum is restored, hope this helps.

Sep 12, 2010 | 2001 Nissan Quest

1 Answer

Warm heat not hot

Check antifreeze level, if it is low coolant may not flow through heater core. If coolant level is ok feel the heater hose with engine running at normal operating temp and heat on high, if one hose is much cooler than the other you have a bad heat control valve or a pluged heater core.

Oct 15, 2009 | Pontiac Grand Am Cars & Trucks

2 Answers

1996 crown victoria has no heat

the temp blend door may not be rotating from the a/c evaporator to the heater core opening.

Could be the motor on the blend door or the temp control knob.

Do you have manual a/c or electronic temp control?

If it's the a/c door electronic actuator motor, it's on top of the plenum. Have to remove the instrument panel for access.

Hope it's the temp knob on the control head.

top one is the circuit you are looking at

Apr 23, 2009 | 1996 Ford Crown Victoria

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