Odd HVAC Behaviour
07-09-2014
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Odd HVAC Behaviour
I am having an intermittent issue with the HVAC in my 2003 EX Coupe. At unpredictable intervals, immediately after starting the car, the temperature control will not work correctly, i.e. heat will blow cold (even if the car is warmed up) or the AC will blow hot air. It is so intermittent and random that I have no idea where to start the diagnostic process.
The biggest thing I wish I were able to ascertain is if the AC compressor is engaging when selected to defrost (hot.) I know it is a Honda thing for the AC compressor to engage regardless of AC selector button position if cold defrost is selected, so I feel like if the compressor was engaging when selected hot that may narrow it down to a bad temperature control rheostat in the dash.
Anybody had this problem? Any ideas on what I should start looking at first? Should I just replace the dash controller and see what happens?
Thanks,
EM
The biggest thing I wish I were able to ascertain is if the AC compressor is engaging when selected to defrost (hot.) I know it is a Honda thing for the AC compressor to engage regardless of AC selector button position if cold defrost is selected, so I feel like if the compressor was engaging when selected hot that may narrow it down to a bad temperature control rheostat in the dash.
Anybody had this problem? Any ideas on what I should start looking at first? Should I just replace the dash controller and see what happens?
Thanks,
EM
07-09-2014
#2
Re: Odd HVAC Behaviour
Yes, AFAIK the compressor is used during defrost. You can tell when it's on because the compressor is located on the driver's side of your engine bay and should only work when it's activated. If you don't know where it is, just look in that area with car running and the A/C and defrost OFF. Make a note of which belt isn't moving. Make sure it IS moving when you turn the A/C or defroster ON. You can usually hear a difference with the engine noise too!
07-09-2014
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Re: Odd HVAC Behaviour
Yes, AFAIK the compressor is used during defrost. You can tell when it's on because the compressor is located on the driver's side of your engine bay and should only work when it's activated. If you don't know where it is, just look in that area with car running and the A/C and defrost OFF. Make a note of which belt isn't moving. Make sure it IS moving when you turn the A/C or defroster ON. You can usually hear a difference with the engine noise too!
07-09-2014
#4
If you think a good mechanic is expensive, try hiring a bad one
Re: Odd HVAC Behaviour
Make a note of which belt isn't moving.
OP must watch the compressor clutch hub to see if it is engaged and spinning or not.
OK the hot/cold thing I guess you need to figure out if the HVAC system is actually changing the blend door (temperature control) modes
or if there is something else going on. Or not going on, since some things may be normal....
immediately after starting the car,
the AC will blow hot air.
the AC will blow hot air.
Example: you drive along and have the car all warmed up and AC blowing cold, then stop at the store and shut the car off.....
You shop for like 15-30 minutes.......
You come back out of the store and get back in and expect cold air immediately, it's gonna be blowing damn hot until the AC system gets to operating for a few minutes and internal pressures are where they need to be to take heat out of the cabin air.
I wish I were able to ascertain is if the AC compressor is engaging when selected to defrost (hot.)
The AC button will not illuminate when defrost is selected, even though the AC may run.
07-09-2014
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The BELTS are always moving when the engine is running.
OP must watch the compressor clutch hub to see if it is engaged and spinning or not.
OK the hot/cold thing I guess you need to figure out if the HVAC system is actually changing the blend door (temperature control) modes
or if there is something else going on. Or not going on, since some things may be normal....
They will do this....
Example: you drive along and have the car all warmed up and AC blowing cold, then stop at the store and shut the car off.....
You shop for like 15-30 minutes.......
You come back out of the store and get back in and expect cold air immediately, it's gonna be blowing damn hot until the AC system gets to operating for a few minutes and internal pressures are where they need to be to take heat out of the cabin air.
If the AC system is operable, it SHOULD run when defrost is selected, regardless of temperature selected. Job #1 of any AC system is to dehumidify the air and that's exactly what the front defroster (defogger) system must do.
The AC button will not illuminate when defrost is selected, even though the AC may run.
OP must watch the compressor clutch hub to see if it is engaged and spinning or not.
OK the hot/cold thing I guess you need to figure out if the HVAC system is actually changing the blend door (temperature control) modes
or if there is something else going on. Or not going on, since some things may be normal....
They will do this....
Example: you drive along and have the car all warmed up and AC blowing cold, then stop at the store and shut the car off.....
You shop for like 15-30 minutes.......
You come back out of the store and get back in and expect cold air immediately, it's gonna be blowing damn hot until the AC system gets to operating for a few minutes and internal pressures are where they need to be to take heat out of the cabin air.
If the AC system is operable, it SHOULD run when defrost is selected, regardless of temperature selected. Job #1 of any AC system is to dehumidify the air and that's exactly what the front defroster (defogger) system must do.
The AC button will not illuminate when defrost is selected, even though the AC may run.
Also, there is no questioning when it is acting up. I bought the car new, I know how long it takes to heat up/cool down. Something errant is going on inside the thing.
07-09-2014
#8
If you think a good mechanic is expensive, try hiring a bad one
Re: Odd HVAC Behaviour
I was just pointing out that an AC system can blow 'heated' air under certain conditions even when working properly.
--------
So it would seem you need to determine whether or not the blend (temperature) door is being controlled (moving) at the wrong times.
If it is, then it's a HVAC control related issue.
If not, then it's something else entirely different.
----------
A heater core with a trapped air pocket may blow cold air at seemingly random times.
It's one of the first noticeable symptoms of a blown head gasket.
Not the only possible cause, but a very common cause.
If your engine is overheating, the computer can and will shut off the AC compressor.
Again, another symptom of a blown head gasket.
Not the only possible cause, but a very common cause.
HTH
--------
So it would seem you need to determine whether or not the blend (temperature) door is being controlled (moving) at the wrong times.
If it is, then it's a HVAC control related issue.
If not, then it's something else entirely different.
----------
A heater core with a trapped air pocket may blow cold air at seemingly random times.
It's one of the first noticeable symptoms of a blown head gasket.
Not the only possible cause, but a very common cause.
If your engine is overheating, the computer can and will shut off the AC compressor.
Again, another symptom of a blown head gasket.
Not the only possible cause, but a very common cause.
HTH
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