Hello,

This is my first post but this forum has been an incredible resource.

BACKGROUND
I bought the car (2001 S_Type 3.0) last Sept with 123Kmi and it is relatively unmolested. AC and heat worked as intended. I don't know the cause of failure but shortly after topping up my coolant reservoir with about a quart of the wrong stuff, I started getting full on heat. Or more specifically, cold AC until the heat overwhelms it. My assumption is that my AC works fine but I screwed up my DCCV valve operation.

I thought both driver and passenger side went hot but the center passenger vent gets hot from proximity to the center driver vent. So I can't be certain if both driver and passenger sides went bad or only the driver side as I never reached across to the passenger window vent to see if that stayed cold. (I only bring this up because it is the current failure mode as you will read)

After completely researching the functionality and potential failure modes I started my repair. As a baseline of my DDCV / ACCM knowledge, here is what I think I know:
1] DCCV is electrically a 3 pin device. Pin 1 controls the driver side relay, pin 2 is VBATT, pin 3 controls the passenger side relay. Pin 2 is always hot (VBATT) regardless of key on/off.
2] When the DCCV fails, the valves stay open allowing hot coolant to reach the heater core. Heater core has 2 sides, driver and passenger.
3] DCCV normal operation:
a] No heat, pin 1 and pin 3 are brought to ground by the ACCM, relays are energized and the valves are closed.
b] High heat, pin 1 and pin 3 are brought to a high impedance state by the ACCM, relays are de-energized and spring loaded open.
c] For temps between low and high, pin 1 and pin 3 are pulsed between ground and high impedance.

ANALYSIS
I jumped right to the replacement of the DCCV since odds are I would be removing the ACCM module anyway. I bought the Ford DCCV valve but as it's been pointed out on this forum the valve bodies still say Bosch. After replacing the DCCV valve and adding the proper coolant, there was no change in the functionality other than that a passenger confirmed that they thought the passenger side vent was staying cold.

Armed with a thermal gun and a multifunction meter I moved to the next step. The thermal gun confirmed that the relay that controls the driver side temperature was staying open regardless of the temp setting and auto/man mode of the ACCM. I next disconnected the DCCV valve electrical connector and measured the voltage on the 3 pin connector using my multifunction meter set for DCV.

My expectation was that on the working passenger side I would measure;
- pin 2 (VBATT) - pin 3 with key off (high impedence) = 0V
- pin 2 (VBATT) - pin 3 with key on but ACCM off (high imedance) = 0V
- pin 2 (VBATT) - pin 3 with key on and ACCM set to high temp (high impedance) = 0V
- pin 2 (VBATT) - pin 3 with key on and ACCM set to lo temp (grounded) = VBATT
Instead all my voltage measurements were = 0V.

On the failing driver side, my expectation was that since the relay stayed open, pin 1 was never being pulled to ground by the ACCM and I would always measure 0V between pin 2 (VBATT) and failing pin 1. My assumption was that failing pin 1 was open circuited (infinite impedence) by a burnt circuit board trace caused when the DCCV went bad. Instead the same 4 voltage measurements were all = VBATT.

Lastly, I removed the ACCM from the dash board and disassembled it looking for any burnt metal traces. There was no evidence of any thermal or electrical damage on either circuit board. I did break my ash tray lid removing the ACCM (grrrr).

CONCLUSION
At this point I assume my ACCM is bad but I would really like to understand the electrical results I've taken. Are there any resistance or current measurements to be taken? I know the current drawn by the relays is an indication of their health but at this point I don't believe them to be a factor.

Any and all insight is welcome.

Thanks and regards,
Ed

 

Just follow the steps: https://www.jaguarforums.com/forum/s...ol-how-185002/

 

Hi,
At last some data that made sense.
1. Reconfirmed pin 2 had 12V (or VBATT).
2. Found a good chassis ground for taking resistance measurements.
3. With engine running and temp set low;
Resistance pin 3 (passenger) to ground = ~ 0 ohm (good)
Resistance pin 1 (driver) to ground = ~ open circuit (fail)
4. With engine running and temp set high;
Resistance pin 3 (passenger) to ground = ~ open circuit (good)
Resistance pin 1 (driver) to ground = ~ open circuit (good)

This implies my ACCM is faulty. I will retake the voltage measurements in my first post just to make some sense of the voltage readings I measured. My measurements were with engine off which may be the culprit. Regardless, I'm satisfied my ACCM was damaged when the DCCV went bad.

Thanks and regards,
Ed

 

Ed,

Do you still have the old DCCV? If so, and you're comfortable with electrical stuff (sounds like it), rig up a fused test circuit to measure the amp draw on each coil of the old DCCV. Per this guide, a good coil will draw 0.6-0.9 amps:

DIY: Diagnose It Yourself - JaguarClimateControl.com

Above that limit? That may have burned out the control module. At that website, you will find info on how to have your module inspected for free, and repaired if needed.


It was previously suggested to look through my HVAC troubleshooting guide. Post #2 there has other details on how to quickly check the operation of an installed DCCV, too.


https://www.jaguarforums.com/forum/s...ol-how-185002/

 

Hi Sandy,

I've had that HVAC troubleshooting guide of yours open on 2 laptops and multiple pages/posts spinning off of it in an effort to learn about the symptoms and repair of the DCCV / ACCM, so thank you very much. The proper voltage measurements required a load on the outputs of the ACCM that connect to pin1 and pin 3 of the DCCV. So I rigged it where I had the DCCV plugged in with 3 wires coming out of the connector for test points. I did not save the old DCCV, but the current (I) readings on the valves on the new DCCV are below one amp. So I'm comfortable the ACCM is faulty, it just would be nice to see evidence of electrical overstress on one of the ACCM circuit boards.

Thanks and regards,
Ed

 

Here's one example:


Curious to know what damage to the CCM board looks like? See an actual photo here! - JaguarClimateControl.com

 

Hello again,
When I say "it sure would be nice to see evidence of a burnt metal trace", it means I've opened up the ACCM module and carefully removed the 2 circuit boards from the plastic housing. After a 1x visual inspection, I see no evidence of a burnt PCB trace like has been attached. Electrically, the ACCM is faulty, most likely the 68pin IC is the culprit. It just would be nice if the damage had been external to the IC. It's kind of like the DCCV valve. It went bad but it never leaked externally. At least I saw the ash tray lid break. I will make a final post when resolved.
Thanks all,
Ed

 

If you do get the ACCM repaired consider adding protection circuitry. The guys at Jagclimatecontrol.com repair offer that too.
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Hi guys,
Just to close out this post. I bought a used climate control module on E-Bay and installed it and the climate control system is working fine now.
Regards, Ed