My '04 2L 4 cyl. manual transmission has a problem with the heater. Every so often, and with seemingly no rhyme or reason, the heater will start blowing cold air through the ducting though the damper switch is in the red (full heat) position.
I believe the thermostat is good (though original), since the temperature gauge goes through a natural deflection from cold to operating temperature and then stays at operating temperature when starting up and driving.
I believe the heater core is good because the cold/hot air delivery changes are sudden, complete, and seemingly random.
For the same reaon, I believe the damper (rotary cold to hot switch) is good because there are positive sounds and a feel as you turn the knob and the damper moves continuously from one point to the next.
The car has a lot of miles (340M), but if anyone has suggestions it would be much appreciated.
Last edited by FE385; 12-18-2011 at 09:03.
Thanks for the response. While I don't think the blend door is sticking, a vacuum problem seems plausible. Now that you have mentioned it, the unpredictable cycling could easily correspond to lower (acceleration) and higher (deceleration) vacuum conditions, especially with accelerator use on a manual transmission.
The cold to hot rotary knob is obviously a mechanical link, but the knob that has the icons indicating directions of airflow, A/C, etc. is vacuum operated.
Is there a vacuum motor for that blender door somewhere in the dash? Would it take a lot of surgery to change it?
Well, for a home mechanic with GOOD tools will take the near part of a day to properly disassemble and categorize the various dash parts and hardware to aid in proper installation after. A day is a solid 8-10hours. A GOOD shop may be able to do this in as little as 6 hours.
The downside is if after you take the dash apart and find that the blend door is operating as it should.
In some cases, and as the years pile on a vehicle the hoses can show signs of fatigue and require replacement. Luck will have it that you won't have to go all the way into the dash, and just behind the HVAC controls.
I know in my Durango I rarely use the HIGH fan setting (it has 4, plus off). On occasion when going up or down a steep hill with the fan on HIGH, I'll hear a pebble or two getting picked up by the fan. Of course it won't come out, but knowingly my day will come when those pebbles will get jammed and stop the fan from turning, or jam into the blend door somehow giving me no temperature control. I haven't had to do this to any vehicle of mine, but I did replace some internals on an older GrandAm sedan years ago and it was a PITA. Took three days with 2-4 hours a day.
It doesn't help any when other people are in the drivers seat and the knobs are constantly being turned. I know in my '99 Taurus for instance, there is a delay of about 3-4 seconds when I change fan mode from say defrost, back onto floor or vice versa. I think to prolong these systems in any vehicle one has to make sure other drivers know to be patient. It's like trying to change TV channels 3 times in a second...won't happen. But in the case of mechanical hardware vs electronics, you can do damage and not even realize it until its too late.
One thing you can check as well, is the PCV valve. there's a small ball in it that should rattle. If it doesn't rattle (it's not very loud), replace it. Another sign the PCV is bad, you'll notice yellow gunk built up on the inside of the oil cap.
There's also a vac line in/around the brake booster. You can pull this line off and put a finger on the end. If you get suction that's a good sign, if not, you might have a blocked tube somewhere (hopefully not in the dash).
I agree that a heroic intervention is too much hassle for occasional cold air, though I do live in MN. It's another annoyance probably related to all the miles. I looked at my Haynes manual and it appears that you can access alot of the control mechanism for the heater just by removing the glove box and climate control area bezel. My number 3 and 4 (middle two) radio presets work intermittently also. Sometimes they work better after the radio has been on for awhile, other times they work only when starting out cold on a winter morning - go figure.
I've always only been the driver of this car - perhaps one of the reasons it has lasted. I do "encourage" rather than crank on the mechanically linked controls - I don't want that bad feeling of stripping something.
Your comment on the PCV valve is intriguing - I've never replaced it. In the old days I used to replace them every tuneup.
If anything you should be able to better narrow down the problem before letting the pros at it with their $100/hr labour costs. The backlight for the LCD screen on my taurus Radio cuts in and out at times. If I push on the top area of the radio the screen turns on momentarily so I can see the time or stereo settings. The board inside has a short in it somewhere but it still works. As the radio in the Taurus is oval shaped (imagine that...) I can't be bothered to get an aftermarket unit and most used OEM units at yards are in poor shape (scratched, cigarette burns...etc).
My 2000 Durango R/T has the old 5.9L V8 in it with all the old goodies, but it's throttle body injection rather than carb. I replace the PCV every two years or 25K miles. For $7, it's worth it. I do a tune up on that every 35-45K depending on how much I towed the trailers.
I found the problem, and wanted to let everyone know in case it proves helpful to them.
The car was low on coolant. I was going through my fall preventative maintenance recently, and was changing the coolant. To my horror, only about 2 quarts of coolant drained out (capacity 5 & 1/3 quarts). The car had also been overheating in the summer, and I thought that all might be explained by a thermostat stuck in the closed position (no coolant circulation).
I had checked the overflow tank before to determine coolant level, even looked inside. However the inside of the tank had become stained and dirty, partly because of the overflow tube that vents down and picks up road dirt. The staining on the inside made it look like there was coolant there looking from the outside and the inside even though there was none. One thing I discovered after cleaning the tank is that there are baffles inside, unlike the overflow tanks of old. The architecture and amount of plastic makes it hard to see the level (plus I have old eyes). I had changed the water pump a couple of years ago, and It appeared to be slowly leaking out the shaft (and that was a new pump). I re-replaced the water pump.
Thanks again for everyone's suggestions, and hope this helps. Everything seems fine now, and I have good heat. Sometimes it's just the simple solutions.
Thanks for the update. Depending on the pump it might have a long warranty on it, even if you installed the last one yourself. Be sure to keep all the receipts. My poor vehicle cabinet is ready to explode with owning all these old vehicles, ha.
The coolant tank in my Taurus is well stained also and a pain to check the fluid level. I just push down on the front end to shake it a bit.
The AutoGuide.com network consists of the largest network of enthusiast-owned enthusiast-operated automotive communities.
AutoGuide.com provides the latest car reviews, auto show coverage, new car prices, and automotive news. The AutoGuide network operates more than 100 automotive forums where our users consult peers for shopping information and advice, and share opinions as a community.