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Old November 7th, 2018, 12:32
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XpedientJ XpedientJ is offline
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Test protocol for '99 Heat Control Switch

Couldn't find any info. via search....

Have the heat/cold<--->hot switch out, and wish to test for proper function.
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Old November 7th, 2018, 12:48
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XpedientJ XpedientJ is offline
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Re: Test protocol for '99 Heat Control Switch

Did, using the center pin, as a common, find that...with the shaft rotated to one end of travel, it shows 16.72 M-ohms on one side pin, and 26.++ on the other pin, with the same readings, REVERSED, with the shaft rotated to the other end of travel....

Does that indicate proper function, by chance...?

Any assistance is much appreciated....

Also, might with to do a direct jumper on the plug, to effect the high-heat position, to confirm system function, beyond the switch....if anyone can advise.
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Old November 7th, 2018, 20:38
Heavyopp Heavyopp is offline
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Re: Test protocol for '99 Heat Control Switch

Whats going on here -- what are your symptoms? What are you trying to fix?
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Old November 8th, 2018, 00:03
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Re: Test protocol for '99 Heat Control Switch

- Typically, no heat coming, when control is max-hot mode, but will usually/eventually come
on after a while...sometimes, only after multiple vehicle uses.

- Core is fairly recent, and has been flushed. NO moving parts in the core, thus, if it does,
sometimes, yield heat, would seem logical that that is not the problem.

- Didn't think it was the issue, but did recently replace the T-stat

- Also, and a more-recent issue, even when there is heat coming through on dash-registers
mode, it goes cool when the defrost mode is selected...

Thus, trying to eliminate potential issues, and it seems there are, indeed, more than one.

Will, next, check vacuum lines to blend door(s)


Thanks for postin-in'....!
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Old November 8th, 2018, 10:29
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XpedientJ XpedientJ is offline
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Re: Test protocol for '99 Heat Control Switch

Further:

- I purchases a use/supposed-good OEM control panel, and the heat-control switch shows
the same readings, and installed performance...

- There does not seem to be a vacuum leak, as door(s) work as they should

- I DID get some fair heat, at one point during testing, but still not what I would expect
given the heater-hoses felt temp. Higher-cap radiator, Hessco pump, modded 'stat
housing, water-wetter, so it does run somewhat cooler-than-stock, but....again,
hoses are HOT.

- Heat output, regardless of control position, is sometimes/sometimes not. This time, though,
when there was decent heat output, the defrost DID retain the heat, where before, as
mentioned, the heat would go right away when defrost was selected.

I must, then, by process-of-elimination, conclude that whatever the mechanism is that
controls actual heat-in, is faulty... The switch is, of course, electrical, but...I believe
the inner control is vacuum-actuated?

Don't remember what is in there, from the core replacement process a few years back.

Thus, perhaps someone can advise just what the control unit is/looks like, where it is located, and whether or not it can possible be accessed without pulling the whole dash out, and the heater box, again.

I do note what appears to be a relay, mounted front and outside on the heater box, behind the glove compartment ; and...a white flange in and behind that, on the heater box, with
an electrical plug. Might those have anything to do with heat control?

Again, thanks very much for any/all assistance.....
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Old November 8th, 2018, 10:47
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XpedientJ XpedientJ is offline
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Re: Test protocol for '99 Heat Control Switch

From some further searching, it appears that:

- Behind the white flange, is the blower motor resistor...

- The 97-01 does NOT have a HCV/heater control valve and, thus, that hot-water flow is
constant, always-on...??? - And, if so, it is purely a blend door that controls temp??
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Old November 8th, 2018, 11:38
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Re: Test protocol for '99 Heat Control Switch

With the dash swung-away, box removed, at 2:08 this gent mentions a vacuum line...that 'goes to the heater control', as he points to a spot un underneath the windshield...??

https://www.youtube.com/watch?v=btoxTq_yGjY
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Old November 8th, 2018, 12:03
lawsoncl lawsoncl is offline
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Re: Test protocol for '99 Heat Control Switch

Broken blend doors are common. If you can get to the blend door actuator, I'd remove that and check if door moves correctly and the whether actuator rotates when you turn the hot/cold adjustment. The controller looks like this https://www.rockauto.com/info/952/95...20_1__ra_p.jpg. It's electrically driven, not vacuum.



This guy has a writeup, but focuses mostly on fabricating a new door after you pull the dash.
https://www.instructables.com/id/DIY...-Door-Failure/


This site sells a kit to replace a broken blend door without pulling the entire dash.
https://heatertreater.net/jeep-cherokee.
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