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Discussion Starter · #1 ·
Its getting cold and my 97 vulcan has been running cooler than i thought it
should. Heats been luke warm. Flushed out the heater core for good
measure. Good flow, clean fluid when done. Hooked up the scan tool,
it been running around 135/140 temp or so. But, it seems with the heater
on, the cooling fan seems to be cycling. Now, this is heat only without
defrost so as i thought i understood it, the fan should not be forced on
like it is with the AC running. So my dilemma is, why is the darn fan running
at that cool of a temp? IF the scan tools is reading 135/140, and the CPU signals the fan on at 215 or so, why is the dam fan cycling on and off?
once in awhile it does jump up to 205/215 or so. something is obviously
intermittent. I am trying to find a CCRM to swap in, but have not got
that done yet, Any ideas?

It seems to the the fan is coming on too soon not allowing the motor to heat up when its cold. Outside are temp seems to be OK on the scan too.
 

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check your high pressure AC Sensor, the one with 4 wires, Mine broke and fan were always running...
 

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Discussion Starter · #4 ·
Flaky ect, thermostat, relays?
Well, here is what i do know. The water temp on the dash gauge when
its not too hot is about a little over a 1/3 of the way up. Its not jumping.
Note this sensor does NOT control the computer or the fan. I have been
monitoring the ECT (which DOES control the engine and fan) and its
consistent on the scan tool 135 or so when this is happening.
and the cooling fan is cycling. If the scan tool is showing the ECT that
parallels the dash gauge, i would tend to believe both temp senders are
ok. That leaves the ECM, and CCRM relay module, or other wiring such as
AC.

Its my understanding the fans run when the AC is switched on. Just heat
alone should not trigger this unless the window defrost is on? I suppose there could be some problem in the dash swtich, but i don't see this a likely.

I know if you unplug the ECT, the fans will run also. But the scan tool is showing good reading. If the circuit was intermittently open, the scan tool should show a out of scale reading

as far as the four wire AC cutout switch goes, i have never played with
this before. but would it trigger the fan with the ac off?

I know there is a temp sensor in the trannie. I have NO way of monitoring it, and not sure if it can command the fan on.
 

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^^^^^ Yes, the fans will run on high speed whenever the AC comp runs. There is a time delay that runs the fans for several seconds after comp cycles out. When triggered to run via ECT, they will run on low speed and only switch to high speed if temp continues to climb. PCM will turn on low speed around 210 deg, and will switch to high speed if temp continues to climb to around 220 deg (I forget the exact temp values programmed in the PCM, and it seems to change somewhat from year to year).
 

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Today I disconnected the high pressure AC Sensor, the one with 4 wires. The fan does not come on when cold or cycle on and off. The problem goes away, except the a/c doesn't work. Not a fix, but identifies that the problem is in this circuit.
 

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Discussion Starter · #11 ·
mine seems to be running warmer now with it disconnected. I had it disconnected since i IM'd you to try it on yours. Now, why it would make any difference is beyond my thinking. The AC should be off. The only thing i can think of is the High pressure switch is malfunctioning making the computer think the AC pressure is too high and it defaults to fan on whether the AC is on or not. Assuming it is the four wire AC switch, i hope it has a scharader valve or such on it so the sensor can come off without draining all the R134 out of the systems. If anyone knows about this, chime in
 
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