QuestionQUESTION: The heater and defroster blow cold unless I hold the engine above idle speed - 1000+ rpm. At idle I get only cold air from the heater/defroster ducts.
Outside temp this morning 30F.
ANSWER: I'm only 4 nominations behind!
Please 'rate' my answer below, and thank me with a "Yes"
The deadline is Thursday the 31st at 4 pm CT
Your help is most appreciated, Charles
Hi Charles,
Earlier this month I answered your question about your car and hope that is is repaired now. I have a favor to ask:
I am competing to be recognized as 'volunteer of the month' at this site. Would take a moment to click on the "Thank/rate the expert" button below? You will then see a question which asks whether to nominate me for that award. If you then click on "yes" that would give me another vote. Thank you for your help.
Roland
Hi Charles,
Two broad possibilites are that there is a problem with the air handling of the unit under the dash, or that there is a restricted flow through the heater core. The control of the air can be evaluated by a self-diagnostic procedure which is:
TROUBLE CODES FROM THE ATC CONTROL
The trouble codes can be checked with the ATC control if a DRBIII® scan tool is not available. The control head can only be placed into the diagnostic mode while the engine is running and the vehicle is not moving. Set the control to a 75° F setting (so there is no confusion with the 23-51 Diagnostic Trouble Codes (DTC's)
To place the system into it's diagnostic mode, press and hold the Floor, Mix and Defrost buttons (at the same time) The ATC head display will begin to blink. Release the Floor, Mix and Defrost buttons. Once the control head enters the diagnostic mode, the display on the control head will continue to blink. This occurs until it completes its tests and climate control unit door/actuator calibrations. Then it will display any diagnostic trouble codes that are present in the BCM. If there are no diagnostic trouble codes, the system will return to its normal operation as indicated by the temperature symbol (a C or a F) Diagnostic trouble codes related to the ATC and climate control unit will appear on the display in numerical form. The diagnostic trouble codes are stored in the BCM and can range between 23 and 51. The ATC control can only show one diagnostic trouble code at a time. Under certain circumstances, more than one diagnostic trouble code could be in the memory. To scroll through any additional diagnostic trouble codes, press the Panel Mode button on the ATC control. It is important that no other knob or button is pushed until all codes are read. Pushing any button except Panel Mode or turning a knob will end the diagnostic test without showing the rest of the trouble codes.
The flow issue can be checked by touching the two hoses that go throught the firewall from the engine compartment to the heater core in the cabin. They are located centrally on the firewall, below the hood opening. While the engine is warmed up and idling check to see if the hoses are about equal in temperature. If not, then the flow is impeded and the solution for that is to back flush the core by removing the hoses where they attach to the engine and use a garden hose to flush water from the cooler hose backwards and out the hotter hose.
It is also possible that the thermostat is opening at too low a temperature when idling so that the coolant never reaches 200+ degrees until you are driving. How does the temp gauge read? It should at least get to 1/3 of full scale by idling, though it may take a few minutes. In any case, it is not good to idle the engine unnecessarily to warm it up in cold weather. Better to drive it and heat it up promptly.
Roland
PS Let me know any codes that come from the diagnostics.
PPS Please 'rate' my answer and consider a nomination for me to be 'expert of the month'. Thanks
---------- FOLLOW-UP ----------
QUESTION: Roland,
There are no codes. The temp gauge indicates normal warm up. Even after warm up and driving several miles, at idle the air from the heat/defrost ducts blows cold. I discovered this in heavy stop & go driving on the freeway.
A new thermostat was installed last January when the radiator was replaced (because of collision damage). Is it possible that vacuum lines were misconnected when the repairs were done?
AnswerHi Charles,
Have you tried touching the two heater hoses at the fire wall after the engine is fully warmed up? They should be equally hot. If not then there is an obstruction to that flow, either in the connections between the engine and the heater core or the core itself, or if the coolant level is low then the water pump can't effectively move coolant through the heater core so check the level in the pressure bottle to verify that is not the case. If the test for fault codes went as described earlier then we have to conclude that the issue is not in the function of the box proper (excluding the question of a core obstruction). There might be some debris in that heater coolant circuit from the accident so if the hoses aren't equally hot you would want to remove them at the engine and try reverse flushing with a garden hose to clear it. Put hose on the colder heater hose for a reverse flush.
I doubt that vacuum hoses have anything to do with this as the coolant/HVAC system is not dependent on vacuum sources at all (although they were in past years).
So check the water level and the heater hose temperatures and let me know what you find.
Roland
PS: Thank you very much for the rating and nomination. By the way, the rules of the contest allow for multiple nominations by a single questioner (which is counter intuitive to me, but that is how it is), allowing one nomination for each answer given. So if this answer is useful you may give me another nomination! I am in a close race with computer guru who for some reason scores 90+% nomination rate from his questioners, and also has about 60% of his questions in the private category. I am not sure I am competing on a level playing field.
