Viscous Heater mystery

samse2101 · **Posted:** Tue May 19, 2015 4:26 am

Hi friends of the vehicle with the second IFS in jeep history,

following problem so far:

The viscous heater clutch at my 2,8 Export KJ doesn`t work anymore -> if i short the relay place in the power distribution center both works (relay and the viscous heater clutch).

it seems for me, that the relay get´s no signal from the ECM... :banghead:

what are the parameters to get a signal to the viscous heater relay?

found this in the forum, but what are the OEM parameters?

Quote:

Per GDE

Operates under the following conditions
RPM < 2400
Coolant < 131 Deg
OD Ambient < 44.6 Deg
Pedal < 60%

hopefully,

samse

flash7210 · **Posted:** Tue May 19, 2015 7:54 am

I dont know the exact temperature but if its not cold enough, the vicous heater will not activate.

Relax, its almost summertime. You shouldnt worry about it till winter.
And besides, you dont really need that silly thing anyway.

samse2101 · **Posted:** Tue May 19, 2015 8:48 am

Thx for the quick response...

Yeah i know it´s summer, and normally i´ve always pulled out the relay, but i tried it exactly now for a test of the coupler

Anyway -> if there is someone who knows the parameters, please tell, thx... :wink:

bye,
samse

samse2101 · **Posted:** Wed May 20, 2015 4:43 am

Especially the stock parameter of the max. RPM and the max. pedal position would be nice to know... :wink:

btw: if anyone can read it out of my ECU file, i can send it her/him per e-mail...

thx and bye,
samse

papaindigo · **Posted:** Wed May 20, 2015 9:58 am

I don't think the OEM settings matter much and in any case they are likely not much different from what GDE posted, although you could just email Keith at GDE and ask him, as the only setting GDE messed with IIRC is lowering the cut off point from 145F to 131F.

You say you pulled the relay and jumped the contacts at which point the viscous heater clutch engaged so it's functional. Did you try swapping in one of the other relays as it's possible the relay is bad?

samse2101 · **Posted:** Wed May 20, 2015 11:51 am

Hi,

GDE also lowered the cut off point of the ambient temperature down, or?

Relay was changed with the AC-Clutch Relay on the upper side in the power distribution box and it works normally... :wink:

bye,
samse

papaindigo · **Posted:** Wed May 20, 2015 12:36 pm

I have no clue if GDE changed the outside ambient temp setting; as I said I know they lowered the coolent temp cutoff point so the viscous did not run as long.

Sounds like your problem was a dead relay. If your year round temps do not get lower than say 20F then just leave the viscous heater relay unplugged. If they go lower you will need to replace the relay. My son says having the viscous heater plugged in makes a small but noticeable difference in how soon he gets cabin heat in Nebraska during the winter but not as much as if he plugs in the block heater which he cannot do at work but can at home

samse2101 · **Posted:** Thu May 21, 2015 7:46 am

papaindigo wrote:

Sounds like your problem was a dead relay.

No, maybe i wrote wrong -> the relay from the VHC worked normally at the place for the AC-Clutch relay...

So definitely no dead relay... :wink:

papaindigo wrote:

Sounds like your problem was a dead relay. If your year round temps do not get lower than say 20F then just leave the viscous heater relay unplugged.

20°F are about -7°C -> sometimes we have here about -10°C...

I´ll wait until the temperatures are lower here and take a look again then... :ALONE:

bye,
samse

JBflyer · **Joined:** Tue Mar 28, 2017 9:40 am **Posts:** 9

Was this issue ever resolved? I have the same thing going on. The relay is good but the viscous heater does not activate. Is there a fuse for that?

TKB4 · **Posted:** Thu Jan 02, 2020 10:53 am

Problem could also be the ambient temperature sensor ( or less likely to go unnoticed coolant sensor etc) not "thinking" temp is low enough for viscous heater to engage. One thing I do for quicker engine warmup especially at idle is to turn both front seat heaters on high. This is not to warm the seat but put a little bigger load on the engine for coolant to heat faster but it does help the cabin too.

I would guess the ambient signal it uses is the same as overhead console uses , if so you could check and see if its relatively close to actual outside temp.

JBflyer · **Joined:** Tue Mar 28, 2017 9:40 am **Posts:** 9

I can take a look at the ambient temp sensor. Mine is a sport, so it doesn't have the heated seats or overhead readout.

flash7210 · **Posted:** Thu Jan 02, 2020 4:09 pm

Yes, there is a relay and a fuse.
There is also a connector on the heater for the clutch.

JBflyer · **Joined:** Tue Mar 28, 2017 9:40 am **Posts:** 9

I have replaced the heater and manually toggled the clutch with power directly to the clutch. I just can't seem to find a fuse marked for the viscous heater.

flash7210 · **Posted:** Thu Jan 02, 2020 4:24 pm

JBflyer wrote:

I have replaced the heater and manually toggled the clutch with power directly to the clutch. I just can't seem to find a fuse marked for the viscous heater.

Yeah, I just looked. Cant find fuse either.
sorry :oops:

WWDiesel · **Posted:** Thu Jan 02, 2020 5:24 pm

flash7210 wrote:

JBflyer wrote:

I have replaced the heater and manually toggled the clutch with power directly to the clutch. I just can't seem to find a fuse marked for the viscous heater.

Yeah, I just looked. Cant find fuse either.
sorry :oops:

According to the FSM, fuse No. 21 (20 amp) in the Power Distribution Center under the hood feeds 12v to the Viscous Heater clutch Relay and to the AC compressor clutch Relay Terminal 30 on both Relays. The Relay is labeled: "Cabin Heater" in the Power Distribution Center.
Terminal 87 is the 12v output on the Relay to the clutch when the relay is energized.
Fuse No. 16 supplies 12v input power to the control circuit (terminal 86) on the Relay. It also supplies input power to the control circuit of the AC clutch relay as well.
The ECM controls relays by grounding the control side of the circuit (terminal 85) to the Relays.

Viscous Heater mystery

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