On a cold day, my car's (2002 Taurus) HVAC system will stick in cool mode for a few minutes even if I set the thermostat to heat. This causes the windshield to fog (instead of defog as it's supposed to), which isn't good when driving! A few minutes later, it switches to heat and the fog disappears very quickly. Is that a bad reversing valve? (I'm thinking the pressure isn't enough to switch the reversing valve at first, but it later warms up, so the pressure rises until the reversing valve switches.) Or should I check for bad connections or something with the control circuit? (Keep in mind that it's still above freezing so there's no reason for it to run a defrost cycle.) Note that if it's not very cold, it switches to heat immediately as I set the thermostat, so I believe it's a worn reversing valve or a temperature sensitive problem with the control circuit.
BTW, I did not bother to check the pressures without a better understanding of the system as gauges connected after a reversing valve can be damaged by sudden pressure changes if the reversing valve switches with the gauges connected.
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Originally Posted by A friend of mine who has a Linux kernel named after his girlfriend.
If I was VirtualBox, I could load my virtualization module into Hannah and boot up another kernel in the same address space.
You do know the heater in a car works off of the engine heat, don't you? Until the engine temperature gets up to operating range, the HVAC system doen't have any heat to provide to the passenger compartment.
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I still think you are misintrepreting what you are feeling. Air off a cold engine block will feel like it cooling and obvuously when the ambiant temperature is colder, it will feel colder. A simple test is to let the engine warm up before turning on the heat.
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Sounds like a sticky Thermostat.
BTW New Avatar Star. Is that you?
Based on personal experience, I agree with rsaturn9. A couple of years ago, my heater stopped working (in the middle of winter) and would only blow cold air. Took my car to the shop and they put a new thermostat in and it worked perfectly.
A lot of vehicles use the AC in the winter to dehumidify the air...
I would say practically all do this and I find it somewhat annoying. Sometimes I would like to direct the airflow to the windshield without kicking on the compressor. Most vehicles don't give you the choice.
Back to the OP, how do you know the compressor is actually on? Have you lifted the hood and seen that the clutch on the compressor is engaged?
Back to the OP, how do you know the compressor is actually on? Have you lifted the hood and seen that the clutch on the compressor is engaged?
I did not connect the gauges to check, since they could be damaged if the reversing valve switches. (If the reversing valve switches, a low pressure line could suddenly become a high pressure line and break the gauge needle right off the end stop. That depends on where the gauges are connected but connecting a low pressure gauge to high pressure can damage it.)
I haven't bothered to locate the compressor but the LED display on the thermostat dims for a split second when it is turned on, so I have a clue the compressor is powered on. I might try to find the compressor and measure voltage to make sure it's not a bad connection dropping voltage. (I'm not sure if it's normal for enough voltage to drop to dim the display. But compressors do draw lots of current on startup. Refrigerant dissolved in the oil on a cold day only makes it worse.) I won't be able to check the current draw since the compressor might draw as much as 50A on startup and I do not have an ammeter that can measure that high. (The largest DC ammeter I have is rated to 10A.) But the A/C worked fine so I don't think the compressor is at fault.
Quote:
Sounds like a sticky Thermostat.
The thermostat (digital type if it makes a difference) seems to be integrated with the radio so I would like to check other possible problems first. The thermostat appears to be nonstandard (not sure about the actual board inside, however) and will probably be expensive to replace.
BTW, can anyone tell me where to find the reversing valve and how it's signaled? (e.g. apply voltage to heat or cool?) I'll make sure it's not a bad connection in the reversing valve circuit.
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Originally Posted by A friend of mine who has a Linux kernel named after his girlfriend.
If I was VirtualBox, I could load my virtualization module into Hannah and boot up another kernel in the same address space.
Its pretty easy to tell by looking whether the compressor is on or not (assuming the compressor isn't tucked away out of view). When off, just the pulley spins, when on the whole thing spins.
Its pretty easy to tell by looking whether the compressor is on or not (assuming the compressor isn't tucked away out of view). When off, just the pulley spins, when on the whole thing spins.
Are you really talking about the condenser fan? In that case, the condenser fans do spin. I'm sure the compressor must be running as the display dimming indicates a current inrush during startup.
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Originally Posted by A friend of mine who has a Linux kernel named after his girlfriend.
If I was VirtualBox, I could load my virtualization module into Hannah and boot up another kernel in the same address space.
Don't know if this is still a problem, but you should be able to see the A/C clutch engage and kick on. Or just feel the refer lines to see if they are cold and hot. By the sound of if, it sounds like you have some knowledge. Use a clamp type thermometer to get your line temps.
This is strange that is only happens on cold days. In my civic, if I turn on the defroster, the a/c kicks on too unless I turn it off.
I'll admit I'm not real current on this but to my knowledge autos don't use reversing valves. They "blend" heat from the engine via the heater core. Also I believe the thermostat the earlier responses are talking about is the one controlling the engine block coolant flow and not the one controlling the cabin temp.
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