yeah, that's what I first thought. Which is why I've been dealing with it for the past month. I keep telling myself that it HAS to be working!

But unfortunately I'm getting nothing. I start my truck, pull it out of the pole shed, get out, shut the garage door, get in the truck, and there is NO HEAT FOR ME. None, not even a little bit. Feels every bit as cold as the rest of the freezing cold air up here.

 

I am not too familiar with the scanguage, but the stuff you are talking about (headlights, etc.) are constant draw items. I don't know enough about the rapid heat system, but your scanguage may not be able to pick up a voltage drop on something that has a duty cycle. Try using your scangauge and cycling the headlights quickly, does it read changes when you do this?

 

Based on what I have read I would guess it to be either a signal issue or a power issue, but with out having a scan tool it is likely to be fun to diagnose. With a scan tool you could check for AHCM specific DTC's and monitor the AHCM_V (voltage) and AHCM_CUR (amperage) PID's. I think this one is going to be best left to the dealer...

Some additional info...

HVAC - Auxiliary Electric Heater (DATC and EMTC)

The AHCM (Auxiliary Heater Control Module) activates if ALL of the following conditions are met:

• The ignition switch is in the RUN/START position
• The engine is operating at greater than 500 rpm
• Any ON mode is selected on the HVAC module
• The temperature setpoint is greater than 80% of the highest setting (EMTC only, DATC uses software algorithm based on interior temp and set point)
• The engine coolant temperature is less than 185° F (85° C)
• No alternator faults have been recorded and alternator is not at full capacity

The AHCM deactivates if ANY of the following conditions are met:

• The ignition switch is in the OFF or ACC position
• The engine coolant temperature is greater than 185° F (85° C)
• An alternator fault has been detected or the alternator is fully loaded due to external electrical loads
• The engine is operating at less than 500 rpm
• The auxiliary heat request is NO from the HVAC module (EMTC or DATC)

 

We have been seeing morning temps in the upper 20s for the last week or so. One thing I have noticed is on the coldest days the Rapid heat doesn't seem to work for the first 5 minutes or so. It was working fine but not so much when it's really cold. Based on what I know about how the glow plug system works on this engine, I'm assuming that the glow plugs are continuing to cycle and the current draw from them creates plenty enough load on the alternator to meet a predetermined condition that prevents the rapid heat from engaging.

I have the single heavy duty alternator so your results may vary with dual alternators. This is the best logic I have been able to apply to it. One other piece of advice, rapid heat seems to be the most effective controlling the climate control manually, fan set to medium speed and recirculating the cabin air. If you allow it to breathe the frigid outside air, it seems to really diminish the effect of the electric heat.

On the topic of "it may not have been installed at the factory", I ordered and my sticker reflects the block heater. There is no block heater cord present. I need to get back to the dealer and have this taken care of. Before I get 20 responses that it's tucked up in the frame next to the tow hook or anything similar, I have verified that there is no wiring present all the way to the heater location in the side of the block. These trucks are assembled by humans and humans make errors. It's aggravating, but it happens. At least the block heater cord is an easy fix.

 

Thanks for posting that! I read that somewhere, but didn't remember where. Looks like there's not much I can do to troubleshoot this one.

I have the single alternator as well, and this was what I was thinking as well. There was a noticeable voltage drop from the glow-plugs on my '08, so I figured those could prevent the heater from working.

But when I checked voltage with my scangauge I was moving down the road at 60 MPH, five minutes after I left the house. This way I know the glow plugs were NOT on, and the coolant temp was still well below 185. I think it was around 80 degrees EOT at the time. I was reading 13.9-14.0 volts with the system powered off, and the exact same with the fan on the medium setting and the temperature dial at max.

 

Actually the glow plugs can still be working at 60 mph or whatever other speed you may be traveling at as long as the coolant temp still hasn't reached operating temperature. This comes from the explanation of the glow plug system given us by one of our resident Ford engineering friends. That being said, I would expect that seeing 14.0 volts the glow plugs would not have been active.

Can you do us all a favor and check your voltage A) key on prior to startup, B) key on engine running just after startup for several minutes? It is possible that with these higher output alternators and advanced electronics in this system that we just don't see the voltage drops we did with the older trucks. I'm just curious as I try to be a student of whatever platform I am currently driving. I may just try it tomorrow morning simply using a multi-tester and checking it directly at the battery for lack of a better method at this time.

 

I know the 6.4L glow plugs could be on for up to 2 minutes, I figured the same was true of the 6.7L engine. This is why I waited for more than that to check it out, but now I'm not sure.

I'll go out and do this later this morning. Have to finish clearing my driveway, we got 5 inches last night!

 

720Deere is correct on the GP's... Here is some additional info on GP operation from a earlier post of mine...

It should be noted that the wait-to-start indicator on-time is controlled by the PCM and is independent from the GPCM on-time.

If the ECT is below 140°F (60°C), the GPCM energizes the glow plugs immediately after the key is placed in the ON position. The on-time is controlled by the GPCM and functions on the basis of the engine RPM, engine torque, engine coolant temperature, air temperature, BARO sensor and battery voltage. The primary ones are battery voltage and the engine coolant temperature.

Additional tidbits...

The GPCM provides battery voltage for approximately 2 seconds to rush current and heat up the glow plugs, then drop back to 7 volts lowering the amperage.

The glow plugs can operate up to 20 minutes.

The glow plugs may turn back on at cold ambient extended idle.

 

Good point. I wonder if the truck's logic is programmed differently if a single heavy duty or dual alternator setup is being used. At 1850W and the possibility of other electric devices being active, does it downgrade the wattage output based on the single heavy duty alternator setup? There is a sizeable difference in between the single vs. double alternator total amperage availability.

 

would be nice to know if the dual alternators make the difference, might make them worth ordering

 

If you haven't tried it already, keep the fan low and give it a minute. That doesn't explain the voltage though unless it only works with low fan speed.

 

I just went out and tried this.

Key-on engine off - 11.5 V. I think this is because of the glow plugs being active.

Engine Running - 14.0-14.3.

So I got the voltage with the key on, started the engine, got the voltage with the engine running. I then turned the heater on at the low fan setting.

Noticed no drop in the voltage, was still reading 14.1 V. Noticed the water temp was starting to climb, and I felt a bit of heat coming out the vents. I figured this may have been due to the warmer coolant in the heater core giving a bit of heat, so I ran inside and got my multimeter and thermocouple.

Checking again, water temp was up to 50°, and I was showing 72° at the vents...how is this POSSIBLE?

Played with the on/off switch for the HVAC and listened closely, and I could hear the engine being loaded when I turned it on, but the voltage remained the same.

So in a nutshell the system is working. That's the only possible way I could get warmer temps out of the outlets than the coolant temp.

I feel like a moron.

Thanks to everyone who helped me figure this out...would have felt like twice as much of a moron had I taken it in to the shop for this.

 

...feel like a moron...that's a little harsh...I have to admit I was puzzled about the way mine acted for a while. One morning I remote started the truck but did not go right out. When I got in, 20 degrees out side, I could immediately feel much warmer air softly wafting out the vents. I then determined that the truck was smarter than me. There are many who think that this is not news...

 

The answer to that would be no. Based on design the AHCM would not be allowed to operate if there is not enough juice to run it at full output. It would either not activate to begin with or if the alternator becomes maxed out while it is operating it will just shut down.

The single heavy duty alternator is more then sufficient on a stock truck. Now if you plan on adding a number of accessories that draw additional power to the point where the primary alternator would be maxed out, then it would be worth looking into the dual alternator setup. If you do not have the need for the additional power you just end up with a additional unutilized alternator.

The other thing I am trying to figure out is where this 1850W number came from. I am still digging around for some additional info, but taking into consideration that the AHCM takes its power directly from a fused link to the battery and it being a 125A Mega Fuse I would not expect the heaters wattage to exceed 1500W...

 

It is weird that there is no drop in voltage when it is working. Had I been diagnosing as you were, I would come to the same conclusion.