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Unread 12-19-2002, 08:50 AM   #1
davejr38
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Nothing but Heat!

Help! I have nothing but heat! Compressor engages. No matter what I set the temp at, it blows out constant heat (same temp). Fan speed works OK. Any help we I can begin? Its a 96 Jeep Grand Cherokee Larado Limmited.

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Unread 12-19-2002, 09:01 AM   #2
zrexron
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Me too?

My compressor will not engage. It'll be interesting to hear what you find out. I can bypass the low pressure switch and the compressor clutch will kick it in, but so far I don't know if it's the switch or a freon/134 leak.

BTW: heat-only is a good thing around here this time of year. :-)
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Unread 12-21-2002, 12:26 PM   #3
MJR
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Re: Nothing but Heat!

Quote:
Originally posted by davejr38
Help! I have nothing but heat! Compressor engages. No matter what I set the temp at, it blows out constant heat (same temp). Fan speed works OK. Any help we I can begin? Its a 96 Jeep Grand Cherokee Larado Limmited.
Does one of the A/C lines get cold ?. If not then you have a leak and are low on Freon. If when you turn the temp knob and the temp doesn't change at all then you might be a blend air servo.
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Unread 12-21-2002, 12:28 PM   #4
MJR
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Re: Me too?

Quote:
Originally posted by zrexron
My compressor will not engage. It'll be interesting to hear what you find out. I can bypass the low pressure switch and the compressor clutch will kick it in, but so far I don't know if it's the switch or a freon/134 leak.

BTW: heat-only is a good thing around here this time of year. :-)
You can look at the A/C lines to look for oil wetness. It depends on the year and engine as to what is most common for leaks.
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Unread 12-22-2002, 08:49 AM   #5
Stocker
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Maybe I'm missing something here , but on at least some vehicles, you set the temperature with a knob, lever, or whatever, which controls a valve, usually in the heater hose. This changes the amount of hot water flowing through the heater core. If the valve (or the knob, lever, linkage etc) fails, you may get no heat (if the valve is stuck colsed), or nothing but heat (if the valve is stuck open). Regardless of whether the A/C compressor is engaged or not.

My guess is a failed water control valve. Had it happen on my old pickup.
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Unread 12-23-2002, 12:51 PM   #6
MJR
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Quote:
Originally posted by Stocker
Maybe I'm missing something here , but on at least some vehicles, you set the temperature with a knob, lever, or whatever, which controls a valve, usually in the heater hose. This changes the amount of hot water flowing through the heater core. If the valve (or the knob, lever, linkage etc) fails, you may get no heat (if the valve is stuck colsed), or nothing but heat (if the valve is stuck open). Regardless of whether the A/C compressor is engaged or not.

My guess is a failed water control valve. Had it happen on my old pickup.
Grand Cherokees do not have a heater valve. The control head uses a servo motor to move the temp door on all Grand Cherokees which adjusts between the hot and cold sides to get the temp selected (blend air system).
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Unread 12-23-2002, 04:32 PM   #7
Stocker
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Quote:
Originally posted by MJR
Grand Cherokees do not have a heater valve. The control head uses a servo motor to move the temp door on all Grand Cherokees which adjusts between the hot and cold sides to get the temp selected (blend air system).
Aha! Never too old to learn something! Thanks for the info.
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Unread 06-30-2003, 02:53 PM   #8
automan25
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So does this mean that there is hot coolant always circulating through the heater core?

Is this why all the plastic pieces underneath the dashboard on the passenger side are always radiating heat into the vehicle?
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Unread 07-01-2003, 12:02 AM   #9
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Quote:
Originally posted by automan25
So does this mean that there is hot coolant always circulating through the heater core?

Is this why all the plastic pieces underneath the dashboard on the passenger side are always radiating heat into the vehicle?
Yes the heater core always circulates coolant.
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Unread 07-01-2003, 10:01 AM   #10
automan25
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I noticed yesterday that CSKauto (Shucks, Kragen, Checker) sells a manual heater control valve for the Jeep Grand Cherokee. I may pick one of these up and install it to see if it reduces the amount of heat in the passenger compartment. My biggest concern with it though, is that it may cause the engine to run hotter.
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