Fan Circuit Won't Activate

Gypsy62 · **Posted:** Sat Jan 27, 2018 12:47 pm

My '05 CRD's OEM electric-fan circuit won't energize when the temp gauge reaches 3/4. I already pulled relays to confirm operation (Flash!); fan's high/low is working =circuit good, grounds solid.

This is almost certainly a "data-to-ECM" issue to direct the stock-setup to energize the circuit at the correct coolant-temp.
Reviewing other threads, these are my questions:
- Did CRD's originally have radiator temp-probes? I definitely have a newer radiator, no probe.
- The "battery-tray temp-sensor" (seriously?). Location/appearance? I removed the tray during major surgery and don't recall thinking "what the %$#@ is THAT?"

Is it possible to 'close' those circuits (or any others) so that the only sensor input-data to the ECM is the actual Coolant-temp?
Wouldn't that mod cue the ECM to energize the elec.fan's circuit solely through coolant-temp data?
Thanks!

Keywords: crd overheating over-heating, jeep diesel running hot, CRD electric fan not spinng running operating, crd electric fan problem issue gremlin mystery conundrum debacle head-scratcher hair-puller tragedy, jeep-involved divorce-inducing tryst, etc.

flash7210 · **Posted:** Sat Jan 27, 2018 6:55 pm

Either of these two things will cause the electric fan to turn on.

1. Coolant temperature of 210F.
Are you able to measure your coolant temp?

2. A/C system on.
Is your A/C functional?

Gypsy62 · **Posted:** Sat Jan 27, 2018 9:49 pm

Your advice to "pull the relay" confirmed that the circuit itself is fine. Anyhoo:
Temps: Yeah, I have a beijing laser thermometer. But if the gauge reached 3/4 -on two separate occasions- without the circuit activating? The engine was definitely on the 'hot' side, but far shy of overheating.

AC: I need to refill the r134. I'm fairly certain that the compressor must be inline to fill, so I'll need to reinstall my stock serp stuff (again) which is not thrilling.

What is that going to tell me, really?
Meaning, it seems very odd that the ECU would need a pressurized AC system in order to activate the cooling-fan circuit. That seems counter-intuitive: so if the AC-pressure is low, in winter while towing uphill the car can overheat because the ECU won't energize the fan circuit?

You know your CRD's; I'll shut-up & repressurize the AC system.
It just seems bat-guano loco that faulty-AC could disable the entire cooling system.
Thanks!

flash7210 · **Posted:** Sat Jan 27, 2018 10:11 pm

You don’t have to get the AC working.

Just drive it till it gets hot, stop, pop the hood, and get a temp reading at the thermostat.
If it’s above 210F and no fan, then yes, there is a problem.

Gypsy62 · **Posted:** Sun Jan 28, 2018 2:03 am

I'll laser it, but I feel reasonably confident that the condition of 210f has already been achieved at 3/4 gauge, without fan activation.

Time to test the coolant temp-sensor located @ thermo housing?
It seems like it would have been running funky if the ECU was receiving temp-sensor data saying that it never reaches normal operating temperature.
Trans temp sensor?
Thanks

Gypsy62 · **Posted:** Mon Jan 29, 2018 2:52 pm

Maybe NOT bat-guano loco.
I recall that the gassers were stock-outfitted with only electric-fans unless "Tow Option"ed, which substituted a mechfan.

This is a CRD, not a gasser. It was engineered with a mechanical fan (w/thermal-clutch) to provide primary cooling, independent of any sensors or electronic data.
By design its stock electric-fan* is tertiary; its central purpose is (apparently) to enhance cooling to the...... AC CONDENSOR!
So, if the AC's system lacks sufficient pressure to close its 'system-pressure' switch, the absence of that signal to the ECM MAY prevent it from activating the electric-fan circuit.
The CRD's Brain may not give a vermin-booty that we're mauling the original cooling design; it may still need to hear "Ready!" from AC-pressure before it consents to whirring blades.

Enlightened by a life liberated from the laboratory, our CRD's minds have become wistful, wandering. Meanwhile, back at engineering, our mods are met with sheer horror. The blood-curdling screams of Frau Benz and Vito Mancini can be heard across the pond. And Beyond.

I'll reinstall an AC serp-setup, repressurize the AC, and update.

Actually, I need to temporarily reinstall the stock MF bracket & serp to serve a second purpose; I'm proceeding with the 2nd custom (lower) bracket & the fab-shop needs the precise serp 'lay' atop the wide/flat MF pulley in order to accurately mount/align the new serp-width/flanged pulley on the custom bracket.
I'm also going to examine whether the custom pulley can be located (laterally) to allow one serp-length to serve >1 setup. However, any relocation from the MF-shaft's original axis mustn't impinge on a direct ALT-HB serp-run during AC-delete setups.
Related, those who've pm'd interest in obtaining the 1st "upper" MF-replace bracket (installed/approved) may want to wait until the "lower" is done and tested. Given the combined objectives of VH/MF-delete & added-clearance for a (puller) elec-fan install, it probably makes sense to order the pair at once.

*No electric-fan whatsoever on mine when purchased.

flash7210 · **Posted:** Mon Jan 29, 2018 7:12 pm

I remember testing this a few years ago.
Hot summer afternoon. Jeep parked in the garage running with AC off. And me monitoring coolant temp with torquePro.
The electric cooling fan came on all on its own in the 205 - 210 F range. Again, AC was off.

None the less, here is a simple way to turn the fan on manually.
You will need a SPST toggle switch and some wire.

Bottom left corner of this picture is the fan low relay.

Relay pulled out and upside down. Note where the white wire is connected.

Put the relay back in the socket.
Run the wire to one post on the switch. The other post gets connected to ground (-).

Gypsy62 · **Posted:** Mon Jan 29, 2018 7:26 pm

Manual fan switch:
https://www.dropbox.com/s/etondh6jtiqsb ... 2.jpg?dl=0
(Says You, "There's not enough room behind there". Says I, "there is NOW", lol).

UPDATE: So, the AC now has great pressure. With the serp still AC-routed I plugged-in the fan, turned-on the switch and about a minute later the fan kicked-on (might have activated "LOW" circuit, not high). That was promising.
However, then I reverted to my VH/AC/MF-delete (w/out serp around AC pulley) and repeated conditions but now the fan won't kick-on unless I use my manual switch.
This suggests that activating the stock CRD electric fan circuit isnt as simple as energizing the AC's "ON" switch while the system is passive-pressurized; its pump has to be spinning.

I'll be roadtrip-testing tomorrow and see if it auto-activates at operating-temp. I'm not optimistic, but at least I can toggle the manual-switch as necessary.

Gypsy62 · **Posted:** Mon Feb 05, 2018 5:45 pm

UPDATED:
Well, now the fan-circuit is activating when the temp gauge reaches slightly past 12:00 (= <5 angular degrees right of TDC. I couldn't quickly locate my laser-thermometer to confirm temp).
I think the circuit activates the "High" feed; the gauge quickly returns to slightly left of 'noon'.
This is in the VH/IPB/AC/MF-delete setup, with the AC charged but the serp deleting the AC pump.

This confirms Flash's test results* that in order to energize the stock CRD's electric-fan circuit the AC does NOT need to be switched "ON". Further, my results confirm that the AC pump does NOT need to be rotating.

However, the ONLY change from my previous condition of 'no fan activation' is that the AC system is now "charged". Consequently, it is tempting to conclude that the AC's system-pressure switch is 'passively' impacting the CRD ECU's decision to activate the fan-circuit. If true, that would mean that the CRD vs. Gasser's ECUs have different electric-fan control parameters (excepting tow-gasser w/mechfan). Obviously, the gasser's ECU would not be programmed to cripple its entire engine-cooling capability simply due to a depressurized AC system.

Maybe the CRD's ECU is programmed to recognize a 'pressurized' AC system and then when thermal conditions elevate above normal operating temps it combines those two signals (pressure & heat) to begin cooling the AC condensor. A pre-cooled AC condensor would then provide quicker & enhanced cabin-cooling if/when demanded by driver.

I may well be missing something, but that seems plausible. I don't know what else to conclude from my own tests.
Bottom line, after all this monkey-biz I'm greatly relieved that I now have an ECU-activated electric-fan. Including a manual back-up switch, if necessary.

Cheers

* I just reviewed this entire thread to see if I missed anything. Though I'm not 100% certain, It sounds like Flash's test was with his AC system charged and serp'd.

Fan Circuit Won't Activate

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