The other day I was driving home and my ice cold AC did a complete 180 on me and started blowing hot air. I've been doing some research and as a long shot I decided to try replacing the heater control valve . Has anyone had any experience with this type of failure ? I hear it's possible that when the valve failed that it actually has a possibility of shorting out the climate control modal behind the dash .. Am I possibly looking in the wrong area for the problem ?

 

Your on the right track , the heater control valve is called the dccv (duel climate control valve) and is located behind the radiator about half way down the narow gap , under the coolant tank , search dccv in the search bar there is plenty of info on it , the modual doesn't always blow , but some times will .

 

Datsports , thanks ..... I have it scheduled to be replaced next Saturday so we will see what happens. Went and picked up the Jaguar antifreeze today 86 bucks "ouch" ... Can't wait to see if this will bring the AC back online ...

 

Define "hot air" please. Put a thermometer in the center dash outlet.

If the discharge temp is close to the outside air temp, that would indicate a loss of cooling from the AC system, and not necessarily a DCCV problem.

If the discharge temp is above the outside air temp, that would mean heat is being added downstream of the AC system, via the DCCV. That could mean a DCCV stuck open, as they are spring-loaded that way by default. You could pinch closed the center hose at the DCCV for troubleshooting and see if that gets your cold air back.

 

Could a leak happen all at once ? This was not a gradual drop in cold air, it went from freezing cold to hot air in about two seconds when it happened ..

 

You're probably on the right path thinking it's the DCCV, but I really need you to take a temperature reading at the center duct. I use a chef's pocket thermometer, set me back about $5 at the grocery store. It clips perfectly into the vent.

It's very important to know the temp of the discharge air. As previously mentioned, discharge air near ambient temp would point towards no cooling from the AC system.

Discharge air hotter than ambient is likely from the DCCV adding hot air. This could be the DCCV stuck open (most likely), an erroneous input causing a full hot command (less likely), or a loss of command signal relaxing the DCCV to the spring-loaded hot position.

Also, take a look at the clutch on the compressor. With the engine running and AC on, you should see the face of the pulley spinning. It may cycle on and off, which is normal. This will indicate the AC system has at least some refrigerant and is trying to provide cooling. This will help rule out the possibility of some fault that has disabled the cooling output from the AC system.

But do please get that temp reading from the center duct. Without it, you're spinning your wheels. From there, you can determine if the AC system isn't cooling, or if heat is being added downstream via the DCCV.

 

I agree with you 100% .... Before I get that temp reading let me share a concern with you ... When it happened I shut down the climate control system ASAP because I knew something wasn't right... If I turn the climate control back on, what is the chances I'll short out the climate control module behind the dash ? I've read several stories where the failed DCCV will short back to the CCM .

 

Valiant effort, but it may be moot. Read through the diagnosis section here:

DIY: Diagnose It Yourself - JaguarClimateControl.com

"Even if the CCM is turned off by the user, a non-damaged CCM will continually supply the Ground signal to the DCCV so that the heater core doesn’t continue to heat up the ambient air."

In other words, even though you turned off the control panel, the two solenoids in the DCCV were still energized.

Read through the rest of that website, including the electrical test further down on the diagnosis page. You should be able to do those steps and know with certainty exactly what is at fault.

If your control panel is damaged, I'd definitely have that guy repair yours. He adds an overcurrent protection feature sadly lacking from the factory.

 

OK, DCCV valve replaced. still have the issue. SO , I pulled the CCM.... I see one trace smoked, would this be the only one ? can I just run a small piece of cat5 wire in place of the trace as sort of a jumper ? Is it just more simple to send it in ? I can work solder iron fairly well...

 

You could give it a go , but disconnect the dccv and test the wires when you re fit it , instead of risking the coils in the dccv .
I have seen people just bridge the burnt track and have a win others not so lucky ,
Put a 5amp spade fuse in the bridge as I have seen done seems a great idea !

 

Well heck, I guess I'll just send it away. They put in the protection fuse I think .

 

Regardless of whether you fix the module yourself or send it away, I'd highly suggest checking the amp draw of the DCCV. Your new one may have been bad from stock.

The link above gave instructions how, but that version seemed a little complicated. I can walk you through a simpler method with a multimeter and some jumpers, if you'd like.

Per that link, normal current draw is 0.6 - 0.9 amps.

I'm curious about the fuses that are added. I'd assume replacement requires pulling the module. I wonder if it's possible to add external fuses that are easily replaceable.

 

They're maybe (automatic) resettable fuses.

 

The module was easy to pull once I dropped the glove box... Then it took 4 hex scews to peek into the module ... I have it packaged up and ready to ship tomorrow... Hope to have it back by Friday or Saturday .... Sometime next week at the latest I guess .. I'll diddle around with the volt meter this week and see what the DCCV reads.. I feel good about this working out... Should be back on top with AC soon... On a sadder note, there seems to now be a small leak in the lower right corner area of the radiator .. I noticed a very small amount of antifreeze... I'm not to worried, it don't seem to be a high pressure leak.

 

OK .... AC is now 100% operational once again... The whole exercise reminded me of why I'm not a mechanic while trying to put the glove box back in, throwing ever cuss word I could think at it... So, here is the damage .

The DCCV cost about 80 bucks "eBay", replacement time for DCCV was about 200 bucks. sending the CCM out for fixing was about 120 bucks "shipping included" "eBay rebuild"... The correct Jaguar coolant fluid 80 bucks so, its about a 480 dollar bill to correct the issue... do NOT try to get away with just repairing the CCM . you will just burn it up again. That was on a 2005 4.2 with navigation ...

 

For future reference, any coolant meeting Jaguar specification WSS M97B44-D may be used. This includes DEX-COOL and Motorcraft brands, which can be purchased for about 18$US, or less, at most parts houses.