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Maintenance & Repair Climate Control Problems (Air Conditioning, Heat) - All Cars
791 messages, Last post on Aug 12, 2009 at 12:55 PM
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replace the engine? hey, I have a light out in my bathroom, replacing your engine is just as likely to fix that, too. the damper doors that direct air from various sources to various places have spring returns to some master mix, generally fresh air. virtually everything now uses vacuum motors to make these changes, and there is a vacuum switch or switches to distribute the vacuum. if you don't generate a good engine vacuum (bad hoses, leaking input manifold or attachment to same, broken vacuum motor or control), you won't hold those doors in position under all conditions. there are check valves that are installed several places on a lot of cars that help to keep the door closed for a short time if you are idling and the vacuum drops below what it takes to swing the motor. there have also been any number of vacuum tanks to maintain that pull on the motors. it is not impossible for a vacuum motor diaphragm to get pinholes or cracks and leak all the vacuum out. that should be expected under the hood, however, where conditions change from one extreme to another, and techs spray cleaning chemicals now and again. it is much more likely to have a loose or deteriorating hose at a master vacuum nipple under the hood, or perhaps a vacuum switch in the temp controller was iffy or being pushed around by a lever bent in installation. somebody playing footsie at the firewall might have kicked a hose off a vacuum motor or bent the hose fitting so it leaks. the shop can put a hand vacuum pump and dial on the rig at the engine side of the firewall and see if they can draw and hold a vacuum on the geegaws going into the passenger compartment. if that fails, fix stuff. if it works, an ultrasonic listener can find little leaks in the works inside, like at the vacuum switch or at a motor with a fading diaphragm. rather than replacing parts until the shelf is bare, an hour or half an hour spent in these tasks should be quite useful in diagnosing just what the heck is really wrong. |
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Swschrad makes some very good points about a potential vacuum leak and what relatively simple things to check before letting the dealer blindly replace expensive components. By all means, have your friend make the dealer do these things first. Stickguy... when describing the AC problem, you didn't say whether the air was still blowing cold when it switches to the defrost vents. On many vehicles, the AC system has a cut-off switch that will temporarily shut down the AC compressor when a demand is placed on the engine... such as passing a vehicle, climbing a hill, hard acceleration, etc., so your engine will have nearly all HP available to meet the demand for the task. Your second post sounds a little like this may be happening. You also weren't clear as to your AC control settings when this occurs... are the controls on any setting that allows defrost operation? You said bi-level, but DC vehicles have 2 bi-level positions... floor/defrost and floor/dash vents. It's possible that the controls are designed to direct air through the defrost or floor vents whenever engine load trips the compressor cut-out switch so it keeps the warm, moist air from slapping you in the face. That may sound unbelievable, but it may be "normal" operation. I've owned vehicles that did this and I was told that they were designed to operate for this reason. Definitely check for vacuum problems as swschrad says. I just offer this as another possible cause to look into. A side note here... many people also don't realize that the AC runs to provide dry air for the defroster, no matter what your heat settings are when in defrost mode. If the outside air temp is above 45-50 degrees, the AC runs in defrost mode.
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All, Thanks for the replies. I'm pretty sure the coolant level is ok - I just had an oil change and they re-filled. Also, I've checked it a few times when I was having the problem and it seemed fine. My next step will be to check to make sure the radiator is not blocked with bugs, leaves, etc. If it is something bigger, such as faulty thermostat or any of the other things swschrad suggested, how much will this cost, approximately? How will I know if my mechanic knows what he's talking about when I take the car in (any specific questions to ask that he should know the answers to?). I don't know much about cars so I have to rely on the mechanic's word. Is this a problem I should take to a Toyota specialist, or should any general mechanic know how to identify and fix this? Thanks again - you're all extremely helpful. |
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I have a 1999 Jeep Cherokee Sport . The dealer just charged the system and found no leaks. The problem is that after 5 minutes on the road the AC stops and it starts to blow warm musty smelling air. THe cooling fan works as designed to begin with going on and off repeatedly in a matter of a few seconds.When the AC quits the cooling fan runs all the time. THe cooling fan continues to run even when I switch over to let in fresh air. After having the AC off for a while it will then kick back in for another 5 minutes burst of cold air ,HELP Just had the coolant flushed and replaced. |
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Sounds like the a/c clutch is cycling off and on, so the problem could be electrical and has nothing to do with freon charged or coolant. I am not sure under what conditions your a/c compressor would be switched on and off automatically by the car's computer or sensors or whatever, but for some reason I think this is what is happening. |
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all a/c has an overpressure safety switch that cuts out the compressor in case of high head pressure. I am dating myself here, but in the 70s GM EEVIR valve bodies had a similar protection switch that could act up if you had moisture in the system causing valves to freeze up and excess pressure to build. high-head is usually a sign that you can't get rid of the heat the evaporator picked up from the interior car air, and I would first consider this as the issue. in particular, is the radiator assembly clean, with no gook between the fins? use an old toothbrush on the outside (road side) of the radiator assembly to brush with the fins and get the cottonwood fuzz and dead bugs off, then back flush the radiator assembly with the garden hose...again, with the fins, not crossways against them, because the nozzle pressure can push fins closed... until you have water bubbling out the front. if you still have issues, you need somebody with a full gauge set to clamp onto the system and see what both the high and low pressure sides are doing. if it's not just a charge issue, it is likely that it's repair time. the best hope is that the clutch coil is overheating, popping a breaker, which then puts the a/c back into service. replacing a clutch or a clutch coil doesn't require dismounting the compressor, and won't require work on the pressurized system. anything else likely means pressure work. low gas is not likely to cause this issue as I remember. |
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| I have a 1992 Honda Accord. I replaced the blower motor that is under the dash for the A/C. When i put it back up under the dash it will not blow cool air through the vents. Each time i pull it out and retest the motor you can feel the air blowing, all the speeds seem to be working fine. What am i doing wrong? | |
| Just back from the dealer. They had overcharged the system last week 1.45 lbs not 1.2 lbs. they corrected that. Raditor fan control relay circuit working fine "THis INDICATES the coil clutch/ AC compressor is working intermittenly ." That much I knew!!!! They recommend relacing the whole assembly $450 + 2 hours labor.I sure like a better rational than it "indicates". The check engine light came on for a day but I don't believe they looked to see if any info was stored. Time to get another opinion or another dealer?The cooling fan also runs full time when the AC has kicked off and I switch to vents. | |
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