Hello all. I have an '03 STR that I picked up earlier this year. I love it. However, as winter appeared I realized I had very weak heat. The a/c troubleshooting guide was very informative on how the system works but the checks it had me do did not yield any results. I presumed the dccv originally and swapped it out with a new unit when I installed a pulley/intake with no improvement. The a/c functions beautifully and chills the car quickly. The heat only works if I've driven a bit and only at lower fan speeds. I can "prime" the system if I drive for awhile and slowly increase fan speed but over half and it goes cool again. This made me think it was the aux coolant pump. I was going to swap it out today while doing the serp belts but I tested the pump off the car and it seemed to function as it should. Could it be weak in the car? Could the car not be commanding the pump on for some reason? Any help would be appreciated. I enjoy driving the car but not if I can't defrost the windows!

 

This does sound like the aux pump .
have you checked the fuses . And made sure the connector is getting power to the pump .
heads up the STR has two 12v Aux pumps . The one on the front side of the radiator is for the inter coolers.
the one behind is for the heater.

 

I have checked all fuses. But I haven't made sure it's getting power. I'm not exactly sure how to force the pump to run. Does it run everytime the heater is on? And yes, I pulled the pump that's on the engine side of the radiator. Thank you.

 

I believe the pump runs as long as the engine is running . Along with the intercooler pump .
did you check all fuses or just the ones in the engine bay ?

 

All the fuses I know about. In the bay, in the passenger footwell, and in the trunk. I didn't test any relays though. I guess I'll have to look at the wiring diagram for the the pump circuit.

 

Time to put on my orthopedic thinking cap. No heat is an unusual fault. Typically the problem is the heat won't shut off, because the valves inside the DCCV are spring-loaded open for max heat.

We've got to determine if you have an issue with low coolant temperature, such as a bad thermostat. Or do we have an electrical issue, such as the DCCV never receiving the command for heat? Both sides of the equation have to be working to get your heat back to normal. No point throwing parts at one side if the fault is in the other.

You mentioned a new DCCV. How did you determine the old one was bad? After replacement, did you test the lines with a thermometer? This component has a very high failure rate, so if you tell me it's good just because it's new, I shall hop the next flight to your fair city and subject you to The Norwegian Fish Slapping Dance:


(Note: Only person ends up in the water, and it won't be me...)

So with that out of the way, I would suggest repeating the test of the DCCV as given in the HVAC troubleshooting guide, post #2:

https://www.jaguarforums.com/forum/s...2/#post1714570

Make sure both sides of the DCCV respond properly to the on/off commands. I wouldn't worry about the fuse to the DCCV, as it is the same one that controls the AC compressor clutch. You've said the AC works well, so we know that fuse is good. Likewise, that same fuse also feeds the aux coolant pump, but we are getting ahead of ourselves.

While testing the DCCV operation, point your handy infrared thermometer at the radiator inlet (the upper connection). Make sure you are seeing approximately 200F. If you see substantially less than that, the heater will never feel very warm. This could be a bad thermostat, for example. Be aware the temperature gauge on the dash is deliberately misleading. From about 180F to 230F, the needle is centered no matter the actual coolant temperature. On my car ('02 V6) on a cold morning, I don't really feel much heat at all until the needle reaches the center, meaning it has just passed 180F. Do you have a scanner? It would be very helpful to see the actual coolant temperature while you're driving, as these conditions are much different than just sitting at idle in your driveway. Or if the needle never quite reaches the center, you'd know the coolant is not really warm enough for good heat.

After verifying the coolant is at the proper temperature, and the DCCV is capable of routing this hot coolant to the heater core, let's consider the aux coolant pump. From a training manual, here's a description of how it operates:




The way I read it, if you set the control panel to HI, the pump should operate, except for the first minute after engine start. With the engine at idle, is it safe to get your hand down there to feel if it is running? If not safe (belts, fan, underhood trolls, etc.), there's another way to test it with the engine off. Wiring diagram is here, see figure 06.1 at the bottom right corner:

http://www.jagrepair.com/images/Elec...al%20Guide.pdf

Note how relay R7 under the hood controls the aux pump. Pull the relay and inspect the prongs for any discoloration or pitting caused by overheating. This would indicate a bad relay itself or loose sockets in the fuse panel. There are two ways to proceed from here, and both are very simple:

1) Swap this suspect R7 with another one. R11 is for the fog lights and R12 is for the horn. Make sure either system works, and then you've got a known-good relay to swap in place of R7. Go for a test drive and see if the heat is now normal.

2) With the engine off, connect a jumper between relay sockets #3 and #5. The sockets aren't labeled, but the prongs on the relay are. Look at the relay to determine which socket is which. To jumper the two sockets, straighten a pair of paper clips (or use two short pieces of similar size bare wire). Insert a wire in each socket, and then touch them together. I'm having you use two pieces of wire because you might get a little spark when you make contact. This way you don't damage the sockets in the fuse panel. And in rare cases, the two pieces of wire may fuse together, but you can easily pull them out together. Oh anyways, once you make contact, the pump should run. With the engine off, you should be able to hear it and safely feel it.

One last though, is there any way the pump could have been installed backwards? I'm not familiar with it, and don't know if it is Murphy proof.

 

Firstly, thank you for the effort in helping me diagnose this.

Secondly, I didn't determine the dccv was bad. I was in the process of new supercharger pulley/belt so I figured I'd replace the 168k original as a prevented. It wasn't expensive and the old one looked fairly corroded around the connector. I won't expect it to be functioning now but it is acting the same now as before. I will definitely start with testing it, however.

I had found the wiring diagram with relay and was going to test the relay next. Hopefully it's simple!

 

A few more thoughts:

For troubleshooting, bump up the selected temperature until HI is displayed and keep it there. This bypasses some of automatic features and can help isolate the problem.

If you'd like, pull the connector from the DCCV. By removing power, this should force the internal valves open at all times for maximum heat. This will help rule out an (unlikely) command for no heat.

Run a cooling system pressure test. I'm talking about the device that looks like a bicycle pump and connects in place of the cap on the coolant reservoir. Pump it up to the pressure listed on the cap. Make sure it holds for at least 15 minutes. Test the cap, too. If pressure drops, you've got a leak, even if you don't notice anything. On my '02 V6, twice I've had a small leak and the only symptom was low heater output. I think this is because of the many convoluted passages in the cooling system. Without normal pressure, the coolant flow seems to misbehave.

How much have you driven the car since the cooling system was apart? There's an official bleeding procedure to purge air from the lines. But I'm lazy and have just driven the car. From my limited experience, it took several drive cycles of at least 30 minutes, with full heat selected, before all was normal again.

 

This was it. The relay. Ha. Something so simple and I've been chasing my tail. It looked fine but I yanked it out and jumped the terminals in the fuse block and the pump came it life. I put the aux coolant pump relay in the place of the horn relay and it wouldn't beep. So, relay is bad. Off to the parts store tomorrow to get a replacement and I'll be comfortable.

Thanks again!