2001 V8 blows hot when ac on max cold. I removed the heater control valve and tested it with 12V and both solenoids closed, I checked the plug to the valve and I am getting 14V. What else could be causing this problem?

Howard

 

Hi Howard,

Reading between the lines, did you work through my HVAC troubleshooting guide?:

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


You mentioned getting hot air from the AC system. How hot? Close to ambient or hotter than that? This is a VERY important distinction.

If close to ambient, the AC may not be doing much in the way of cooling. More details in the guide on how to troubleshoot that.

If hotter than ambient, something is heating up the air, namely the heater core. Try clamping off the large coolant return line from the heater. See if the vent temperature decreases. If so, hot coolant was somehow reaching the heater core. Even though your electrical checks passed, there's a little gotcha when testing for voltage in an unloaded circuit. You could have a marginal connection somewhere, such as a spot with multiple broken wire strands. The few remaining strands pass just enough current to show proper voltage when the circuit is tested unloaded. But when the circuit is under load, this connection restricts current flow and the solenoids don't get enough power to operate properly. This happens more than you might realize. I have learned the hard way never to completely trust voltage checks on an unloaded circuit. In this instance, the quickest way to rule out this possibility is to clamp off the coolant return line. Regardless of how the DCCV may be responding electrically, the clamp shuts off all coolant flow through the heater. Then you'd know how to proceed.

 

If the DCCV has not been changed yet. Just swap it out. They will all fail and it's just not worth the time and effort to troubleshoot it. You do know the Lincoln LS part is the same?
If after that if you still have problems post back.
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Hi Karl,
I did follow your posting, in fact I was so impressed that I copied it to a word document for future reference, I put a new valve today and because of other commitments I won't be able to finish the job until next Tuesday.
Thanks for your help
Howard

 

Do you still have the old valve removed? Try testing the amp draw needed for each solenoid to close. Normal current draw is 0.6 - 0.9 amps.

One hunch is either solenoid is drawing more current than specifications, more than the vehicle wiring can deliver, but not enough to blow the 10A fuse. Just a guess, but maybe a bad solenoid was requiring 4 amps, not the normal 0.6 - 0.9 amps. When you hooked up your test jumper, the wire size was probably big enough to supply the extra current required and everything seemed good. But when installed in the vehicle, the factory wiring goes through the control module and might only be capable of supplying 2 amps (another guess) and so the solenoid stalls in the open position and lets heat into the cabin. It's not enough extra current to blow the fuse or damage any wiring, but this shortcoming is enough to prevent the valve from operating normally. If you have the valve removed, it would be easy to test the amp draw and know for sure before replacing it.

I have run into a similar scenario at work on a regular basis. The 737 has several small pneumatic valves to distribute warm air and fine tune the temperature throughout the cabin. These valves have a feedback system to monitor their commanded position. If the actual position disagrees with the command, a warning light will illuminate and typically requires replacement of the valve. Unfortunately, the replacements were also failing very quickly, often within days. For a while, we were seeing at least 3 or 4 per week, if not more. After much wailing and gnashing of teeth, our engineering department found the root cause. When installed on the aircraft, control is via a computer (black box) that was only designed to supply a certain amount of amperage. When failed valves were checked in the shop, the test equipment could supply a much higher amperage. As valves aged and started to fail, they required more power than the onboard circuit could supply. The valves would stall mid-travel and the warning light would illuminate. But when tested in the shop, the valves worked fine with higher amperage available and would be returned to stock as serviceable, only to fail again shortly after installation. The "fix" was to reduce the amperage on the shop's test apparatus, and then they were able to identify and properly repair the bad valves.

Sorry for the long-winded story, but I'd be real curious to hear what you discover if you test the amp draw on your old valve.

 

Hi Karl,
I check the current draw on the old valve but I can't get to it for several days, I let you know the results.

Thanks,
Howard

 

Just remember the DCCV can go out and not show in your testing. I has a friend that tested everything on it and it seemed fine and still did not work. Getting a new one solved his problem. Same 2001 car. The 2001 is a little more robust on the Climate Control unit but can still get blown with a bad DCCV.
Tom in Dallas/Plano
05 S-type 119k

 

Hi Karl,

I had some time to work on the Jag yesterday so I checked the current draw on the heater control valve that I removed and it was 0.92 amp on one side and 1.0 amp on the other side, so it looks like I replaced a good valve. After installing a new heater control valve, I hooked up my ac gages and the low side was reading 25 t0 30 psi and the high side was 95 to 100 psi. The ambient temp was 75F. The radiator fan was turning and the compressor clutch was engaged and turning the compressor. The dash vent temp was 67F.The high side pressure seems too low and the dash vent temp is definitely not cold enough. Any suggestions on the cause of this problem or next steps in troubleshooting this problem?

Howard

 

Get a vacuum and vacuum down the refrigerant and then get a small scale and weigh in the proper amount as listed in your car. I checked Alldata and your specification is 1.76 pounds There are procedures in the forum for proper weighing if you have not done before. As long as your high side was not having a needle jumping around to indicate a bad valve in the compressor, looks like you are low on coolant. Remember that this is done by weight if you are going to be exacting. Also you may want to take time and replace the Drier Desiccant Bag if you have not already done so.

TBB

 

Hmm, those numbers seem pretty close to specs. I don't know how hard and fast the 0.6 - 0.9 amps range really is. I don't see a glaring problem there, at least on the electric side. Still no guarantee the valves were sealing off coolant flow 100%, though.

A couple of thoughts regarding the new DCCV. If access isn't too difficult (HA!), it might be worthwhile checking the amp draw on this unit, too. If not really feasible, I wouldn't make more work for yourself, but it would be good to know. The other option is to simply clamp off the heater return line. This will absolutely, positively shut off coolant flow so as not to skew any further troubleshooting.

Interpreting pressure readings is not my strong suit. I mostly look at the low side reading, and it would appear your compressor is pulling the pressure down properly where it should be on the low side. This doesn't indicate a slipping clutch or drive belt, either. The high side should be higher, but I don't really know what is a "normal" reading would be. There are SO many variables, and the Visteon compressor has a self-regulating feature that makes diagnosis a little tricky compared to basic on/off compressor control systems.

One possibility that comes to mind is low refrigerant, a very common problem. Please see post #4 here for more details on that, including why pressure readings aren't much help to determine refrigerant quantity:

https://www.jaguarforums.com/forum/s...2/#post1714573


In my over-inflated opinion, your car is a good candidate for an "investigative top-off", as detailed at the link. I have no problem gambling your time and money on that. The official party line is to do a full evacuation and recharge when refrigerant quantity is in doubt, but I've had good success trying this if you're willing to roll the dice with a little bit of time and a few buck's worth of refrigerant. Or if you're not Mr. Vegas, a full evac and refill is probably in order.

 

Tom,

Can you please elaborate on this? I'd like to refine the test procedures if possible, for better accuracy.

Presently, I have the DCCV tests broken down into two broad categories. The first category is to measure temperature to see if hot coolant is making it past the DCCV when it should be closed. I've given two methods to accomplish the same thing, either by measuring the heater lines themselves or the duct temperature. If a fault (hot coolant reaching the heater) is confirmed, the next category has some basic electrical checks of power and ground to the DCCV.

Some more details of what your friend experienced would be very helpful, and maybe I can tweak the test procedures.

 

I will ask him to respond to you.

TBB

 

Hi there! I'm the friend that had a similar situation. I no longer own the car (it was for my nephew) I do remember having a heck of a time with the DCCV. I ran all sorts of electrical tests but finally ended up replacing it. Electrically speaking it was fine, but inside the valve was full of gunk which was not allowing it to close properly (the car had been siting for 3 years which didn't help).
Another issue I had was with the head unit itself. I traced the two currents all the way back to the head unit and found that one side was responsive to changes in temperature settings, but the other side made no difference. So I ended up getting a used head unit and that fixed the problem.

Admittedly I was one of those that "throws money" at the problem rather than doing proper testing, but in my case it worked. The DCCV was less than $70 and from what was told that it wasn't a matter of IF they go out, but rather WHEN they go out (by the way, you may already know this but many parts from the Lincoln LS will fit the S-type, only without the Jaguar price tag) so I felt justified in having a new valve regardless of it wasn't the problem at the moment, I figured it would be eventually.

 

Hi TBB,
Thanks for your suggestion. I don't have a vacuum pump. What do you think if I try adding additional R134A in small amounts at a time and watch the results on the dash vent temp and the high side pressure?

Howard

 

The high side pressure tells you about valves. You should be able to get from autozone or Oreilly a pump on loan. Harbor freight has them cheap also. If I had to look I would look at low side pressure and it should be in the 35-40 PSI range depending on the temp.



TBB

 

Hello,
Thank you all for your suggestions, I added 10 oz of R134a to the system and my dash vent temp went from 67F to 45F.

Howard

 

Groovy! Thanks for the update. Glad to hear of the big improvement.

Was that temperature measured while stationary or moving? My '02 will consistently put out 38F air while moving, with all that ram airflow through the condenser. When stopped, the temp might slowly creep up to 42 or so, when the fan is the only thing moving air.

If you're seeing 45F while in motion (expect several minutes to get all the way down to 38F), you may want to continue troubleshooting to get that last bit of cooling performance. Way back to square one, make sure your new DCCV is indeed closing 100%. The troubleshooting guide has two methods to test this.

How long since the refrigerant was last serviced? 10 ounces is a lot to add, so if not much time has elapsed, you may have a leak present. The other possibility is the system is slightly overfilled now, which could explain why things are much better but still not down to 38F.

 

10oz is a lot to add and where did it leak from? Generally 134 systems are less forgiving than R12 and that amount should have caused the low pressure switch to engage and turn off the compressor. Did you have a 10oz can or otherwise, how are you sure it was 10 oz since most cans are 12? What was your outside temp and low side psi? Of course your vent temp on a hot day may take some time to cool down as you build up much heat in the objects in the car- seats, ect and it takes time to get to max cooling under such circumstances if it has been left sitting in the sun for long.

Otherwise, at least for now, thumbs up on get some cool air.

TBB

 

Agree that it looks like you have a leak somewhere with those results.
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Minor clarification here. The only pressure "switch" in the system is the AC Pressure Sensor, if I remember my nomenclature correctly. It's not an on/off switch, but a variable sensor that sends a signal to the controller to indicate system pressure. It's installed on the high pressure side, and if pressure rises above 420PSI, the compressor is commanded off to prevent damage.

It's kinda sorta a low refrigerant protection input, too. With the compressor off, pressure will be equalized between the high and low sides. In the event of a MAJOR leak, and pressure has dropped very low, compressor operation will be inhibited. This is to prevent the compressor from running without proper lubrication. Keep in mind refrigerant pressure behaves weirdly. At a constant temperature, a closed container or system will basically show the same pressure whether full or almost empty. Only when a system is nearly depleted will the pressure finally decay. This low pressure protection is a very last ditch kind of thing, only kicking in just before the system is totally empty.

'Scuse me while I go off on a tangent here, but you've got to be careful troubleshooting this type of AC system. The control system is somewhat different than most vehicles, which commonly used a fixed orifice and a pressure switch to regulate the low side, keeping the evaporator just above freezing. Jaguar used an evaporator temperature sensor as the primary input for control of the compressor. In addition, the compressor has a self-regulating function, too, not found with fixed orifice systems. Some excellent troubleshooting methods from a fixed orifice system will give very misleading results on a Jaguar. Pressure readings are one of the big gotchas, especially on the high side.