Heater Core Replacement Procedures

Generic Procedures
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We have provided this generic information in hopes that it might be useful to you if we don't yet have your specific model listed.

Recommendation: If you need detailed heater core replacement procedures immediately for a 1990's vehicle that are not yet available on our site, you might consider getting a copy of the Chilton's 1990-2000 Heater Core Service manual for your 1990 - 2000 Domestic & Imported vehicles. The manual contains very good step-by-step procedures, detailed illustrations and exploded views.  You can download the Table of Contents to see whether your model is covered before you buy the manual. (The models are not in continuous alphabetical order, so you may have to look carefully through all 5 pages to find your model.)

NOTE:  Most vendors charge from around $45.00 to over $90.00 for this manual (over 700 pages). The cheapest we've found is around $30 at Amazon.com .

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Heater System Inspection

Source: AutoZone.com

The heater core is a small heat exchanger that engine coolant is circulated through. It is usually located inside the driver's compartment.

When performing any checks and service procedures, always follow the procedures recommended in the manufacturer's service manual.

In most cases, problems with the heating system are problems with the engine's cooling system. Therefore most service work and diagnosis is done to the cooling system.

Coolant flows through the heater core to warm the passenger compartment.

Problems that pertain specifically to the heater are few: the heater control valve and the heater.

  • Most often if these two items are faulty, the engine's cooling system will be negatively affected.
  • Both of these items are replaced rather than repaired.
  • In some cases, it is possible to make repairs to vacuum hoses and electrical connections without removing the heater assembly.

When there is a problem of insufficient heat, begin your diagnosis with a visual inspection and a check of the coolant level.

If the level is correct, turn the heater controls on and run the engine until it reaches normal operating temperature. Then:

  • Measure the temperature of the upper radiator hose.
    • The temperature can be measured with a pyrometer.
    • If one is not available, gently touch the hose.
    • You should not be able to hold the hose long because of the heat.

CAUTION
While doing this, make sure you stay clear of the area around the cooling fan. A spinning fan can chop off your hand.

  •  
    • If the temperature of the hose is not within specifications, suspect a faulty thermostat.
  • If the hose was the correct temperature, check the temperature of the two heater hoses.
    • They should both be hot.
    • If only one of the hoses is hot, suspect the heater control valve or a plugged heater core. Like the radiator, heater core tanks, tubes and fins can become clogged over time by rust, scale, and mineral deposits circulated by the coolant.
    • Reverse flushing the core with a power flusher may open up the blockage, but usually the core has to be removed for cleaning or replacement.
  • With cable-operated control valves, check the cable for sticking, slipping (loose mounting bracket) or misadjustment. With valves that are vacuum operated, there should be no vacuum to the valve when the heater is on (except for those that are normally closed and need vacuum to open).
  • Water on the front floor mat or passenger compartment may indicate a leaking heater core. Complete the following diagnostic checks:
    • Check the liquid to see if antifreeze is mixed with the liquid. It should be oily if it contains antifreeze.
    • If it is oily, check all hose connections for leaks.
    • Check the drain passageways to make sure they are not clogged with foreign material.
    • Use a pressure checker to test the pressure in the cooling system. this procedure may detect a small leak in the heater core.
  • Air pockets in the heater core can also interfere with proper coolant circulation. Air pockets form when the coolant level is low or when the cooling system is not properly filled after draining.
  • Flush the cooling system and replace the coolant seasonally.

 

Heater Core Replacement

If it is necessary to remove the heater assembly, the cooling system must be drained before removing the heater core.

When a heater core leaks, a new heater core is installed or the old one repaired.

Heater Housing

  • The heater housing is usually under the dash and must be removed to gain access to the heater core.
  • Procedures for replacing the heater core vary with the year, make, and model of car. It threfore necessary to consult the manufacturer's repair manuals for the proper procedure for replacement.

The heater housing is disassembled to get to the heater core.

Heater Core

  • Remove the access panels(s) or the split heater/air conditioning case to gain acess to the heater core.
  • Remove the heater coolant hoses.
  • Remove the cable and/or vacuum control lines (if equipped).
  • Remove the heater core securing brackets and/or clamps.
  • Lift the core from the case. Do not use force. Take care not to damage the fins of the heater core when removing.
  • To reinstall the heater core, reverse the removal steps.

When the heater core leaks and must be repaired or replaced, it is a very difficult and time-consuming job primarily because of the core's location deep within the firewall of the car. For this reason always leak test a replacement heater core before installation.

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