The A/C on my 2003 S-type has come up with a new odd behavior. Could anyone give me a guess as to what's wrong?

Here's what it does: Around town, on short trips, it seems to work normally, but on long drives, after about 60-90 minutes, it gradually stops blowing cold air (or even hot air) through the vents. I can crank the fan up to full blast and hear it roaring, but my hand on the vents feels just barely a trickle of cold air -- and eventually nothing at all.

Switching the controls to defrost or to heat makes no difference. Nothing comes out the defrost vents at the windshield, and you barely feel anything when reaching underneath where the heater vents are. The fan is working fine -- I can hear it roaring. And the slight trickle of ice-cold air tells me the compressor and other parts are functioning as well. It's just as if all the vents have been shut down.

If we stop for 5 or 10 minutes and restart it works fine, but only for a few minutes before the air is cut off again. I tried searching for other threads that tackle this but haven't been able to find any, although I did find some that discuss the AC blowing hot out of one vent and cold out of another. That seems to be caused by a faulty DCCV, located in the dash. But there are a couple other electronic control modules involved in this and I don't want to just start replacing them at random. Any guesses as to which one? Or some other cause?

Thanks in advance!

 

Does this happen when you have heat on? If it only happens when you have it set to "cold" then it could be due to ice forming around the core. Air conditioning systems are supposed to cycle to stop this happening. Once it happens it will take a while for the ice to melt.

 

If your car is still running its factory compressor, I would bet that it is gradually dying now. Your symptoms sound very similar to my 2005 S-Type in May 2010. The A/C became less and less effective, especially as outside temps rose into the 80s. Eventually it quit cooling at all. A new compressor restored my system to ice-cold A/C again....

I also initially suspected the DCCV. But a check-up at a local A/C shop confirmed that my compressor was indeed on its way out. Unfortunately, it is a relatively common issue with these cars....

 

Very good advice!

Check the bottom of the compressor for yellow/green stains. Another sign you need a replacement. The good thing is they are very cheap since the Lincoln LS uses the same one.

Be sure and change the filter/dryer too. Most compressors won't have a warranty unless you do.
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Thanks for the good advice, but in this case I think the problem is not the compressor. The compressor is brand new -- replaced last summer. And, as I mentioned, if I hold my hand up against the vent I can feel just a trickle of very cold air, which would seem to mean the compressor is doing its job. The problem is that the air doesn't blow out of the vents, even though it's being chilled and even though the fan is roaring a full speed. It's as if the vents get shut off or blocked after about 60 minutes or so of operation.

Jackra, that's a good question about whether it does this when operating the heater as well. Unfortunately, I may not be able to answer it. I live in South Florida and have never operated the heater on this car for more than a couple of minutes. There's nowhere I can go to drive with the heater on for an hour or so to see if the same problem crops up. You could be onto something, though: Perhaps when the compressor was replaced last summer, something was overlooked which causes it to run constantly, rather than cycle on and off? I don't know the plumbing of the air ducts, but I suppose it's possible there's a tight corner or restriction somewhere where ice could form after extended operation and block the flow? Sounds like a long shot but I'll look some more.

Thanks for the ideas -- and I'd still welcome any other thoughts!

 

Failing compressors still blow cold air, just restricted cold air that gradually fades to ambient temperature. From your description that is still the prime suspect in my eyes....

The second suspect would be the servo motors that control the vent flaps. Do you hear them "hunting" when the HVAC is running, and sometimes even after you shut your ignition off? Some folks describe them as "bubbling" sounds....

 

I mentioned this because I have this problem with my 2006 Dodge Dakota.
In the Summer, especially with high humidity, the core clogs up with ice after a while. I can actually see it. It takes quite a while to melt before I can use the air again. I discovered the cycling issue when I researched the problem.
Also IF there is some sort of blockage in that area so that cold air cannot blow through "unrestricted" other than normal restriction, that could cause more of a problem.

 

What you've described is not "odd" behavior but quite normal for an a/c system that is low on refrigerant charge. Jackra has nailed it that you are forming an ice block that eventually clogs the evap core. Sure, it "could" be caused by a malfunctioning TXV or perhaps a few other things. But most likely a very small leak in your system. As Jon said, the comp seal is a common culprit. Look for oil residue around the shaft and at all a/c pipe joints. Have it evacuated and recharged with the proper qty and type refrigerant and it will stop doing this, most likely.... but the problem will recur if you have a leak.... unless you just got a bum charge when the comp was replaced.

 

Well, it seems it's just about unanimous that this is a compressor problem. So I'll be taking it back to the mechanic who replaced the compressor last summer. He's been very good and cooperative (and relatively reasonable in price), so I'm pretty confident he'll make it right if something was done incorrectly last summer.

But I have to admit I still have doubts that this is really the problem. Having lived in South Florida for 30 years, I've replaced a LOT of A/C compressors over the years in all kinds of cars, and I know the pattern: the air coming out gradually becomes less and less cool until finally the blower fan is just blowing warm air into the cabin.

But that's not what's happening here. The system is still producing ice cold air, even after several hours. It's chilling the air fine. The problem is only the slightest trickle of anything is coming out the vents. It's a matter of volume -- not temperature. And it doesn't matter which vents I select to route the air through -- the windshield defrost vents, the vents at your feet, or the vents on the dash. The air coming out is still ice cold -- but the volume of air gradually slows to barely a trickle, and eventually no air of any kind -- hot, cold or lukewarm -- is moving out of the vent. The vent grill is still cold, and what slight trickle of air you feel is still ice cold. But there's no volume of air, even though the blower fan is still roaring.

I actually think Jon 89 may be closer to the answer when he he mentioned the servo motors that operate the vents (or, I'd suggest, the control module that tells the servo motors what to do). But I guess I'll start with the compressor since that's the consensus choice and the mechanic who replaced it is a straight-shooter.

Thanks again for all the good advice.

 

If you let the car sit for an hour or two after one of these events, is there a huge puddle of water underneath?

 

Mikey, there's always a puddle, of course. I didn't notice it being exceptionally large lately, but I didn't really pay attention. I will next time, though. I assume you're thinking about Jackra's suggestion of an iced-over evaporator coil. The more I think about it, the more I'm starting to lean that way too. I didn't realize that a system that is slightly undercharged with refrigerant could cause that, but in reading up on it I think I get why. I suppose the logical next step is a pressure check and, if it's low, a check for leaks. Thanks.

 

I did not know that an undercharged air conditioning system could cause the ice up. I do have a very slight leak in my Dodge Dakota air system and I do recharge it at the beginning of the Summer. So will watch this more closely on the Dakota.

 

As a work-around, you can manually cycle the compressor with the A/C button....as soon as you sense a degradation in airflow, turn comp off but keep fan on high, when airflow is restored, turn a/c back on....but this will be a cycle that will get old quickly....60 sec on and 30-90 off type thing....also, run your system in recirc mode to minimize the amount of condensate that precipitates out on the core and becomes ice....though I believe the system will automatically switch you back to fresh-air after 15 mins or so, so you will have to stay on top of it.

The "failing compressor" that acts like this is not failing in its compressive capacity...the common failure we've seen is between the refrigerant and the shaft seal, so you get a slight leak past the shaft....it is still compressing gas just fine, but the "repair" is compressor replacement - though that one is a good candidate for a rebuild.

If you are low on refrigerant due to a leak, your compressor will eventually stop engaging it's clutch due to the low-pressure switch - there just won't be enough refrigerant to trip the switch to complete the clutch ciruit - a low charge protection measure for the comp because the oil is in suspension in the refrigerant and engaging the comp without refrigerant (and lubrication) will eventually destroy it. That is why you should see an oil/dust residue where it is leaking. The oil precipitates out as the refrigerant escapes the surly bonds of the closed-loop system!

If you have good system integrity, but are simply low on charge because enough wasn't put in at the last service, it will probably continue this way indefinitely.

I trust you are not still under warranty....many a TXV has been returned under warranty because the shop cannot get paid for a simple "evacuate and recharge" so if no leak can be found.....change the TXV (or orifice tube on suction-accum systems) and customer drives away happy and dealer gets paid. Frequently, a fresh charge (which is a by-product of almost any component change on an a/c system, save pressure switches when schraeder valves are present) is the real fix.

 

Hope it's not an expansion valve problem because that requires the dash to be removed and that's a big job!

You tend to have more rattles and squeaks after the repair too.

The good thing is that problem is very rare on the S Type and unless it gets clogged from debris in the system it should be good.
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Maybe an undercharged a/c works continuously, due to the struggle to get cold enough, instead of the more normal cycling on and off - and thus ices up whereas a properly working one has a chance for the ice to melt and drain away as water during an off cycle.

 

Hello Gary, I realize this is an old thread but I am curious if you were you ever able to resolve this? If so, how? I was so excited to find your thread as this is the exact same issue I have with my 2000 s-type 3.0.


"after about 60-90 minutes, it gradually stops blowing cold air (or even hot air) through the vents. I can crank the fan up to full blast and hear it roaring, but my hand on the vents feels just barely a trickle of cold air -- and eventually nothing at all. "
Many thanks!

 

My guess is that the temperature sensor at the evaporator is faulty and causes the evaporator to frreze. When this happens, ice blocks the flow of air.

 

Was my best guess (post 15) as well. Only way to tell is investigate...

 

Interesting thread to read, with the same symptoms on a second car. OP, are you still here? Curious what the fix was.

What are you feelings on gambling? Would you rather take it to a shop and have it fixed in one fell swoop and know it's right? Or are you like me and willing to invest/gamble a little of your time and money, with a very realistic chance of an inexpensive fix?

When was the last time the AC was serviced? If it's been 3 or 4 years, the most likely culprit is a low refrigerant charge. No matter how well the system is sealed, you can expect the system to slowly bleed down.

Or has the AC been doing this for a while, and was recently serviced with no change? In that case, I'd lean towards the evap temperature sensor. It's a MotorCraft YH1504, and will set you back about $20. You've got to stand on your head under the dash to change it, but it goes quickly and is a reasonable gamble.

If it's been a while on the AC service, I'd lean in that direction. Carefully look over the compressor and exposed lines for any stains from leakage. If you don't see any smoking guns needing repair, a recharge is a good gamble. Per the party line, a full discharge, deep vacuum, and measured refill is the way to go. Then you'd know the system has the proper amount of refrigerant.

However, cheap and lazy as I am, I've had good results with what I'd call an investigative top-off. Rather than do the full service, you can try adding a SMALL amount of refrigerant, maybe 3 ounces. See if the condition improves. If so, add another SMALL amount. The secret is to STOP when you see no more improvement. That's the hard part. I've had about an 80% success rate over the years with this.

If it doesn't work, do more troubleshooting, repair the fault, and then do a full evac and recharge. I've caught a lot of grief here suggesting the top-off method, but as long as one is aware of the potential shortcomings, I think it's worth a shot. I've never damaged anything this way. If accidentally overserviced, the pressure sensor won't let the compressor run, that's all, and you'll have wasted a little of your time and a partial can of refrigerant.

 

Thanks all for the added input. Here is what I (or mechanics, rather!) have done so far. The problem started a year ago. I live in NYC so don't drive much, especially longer trips, which is when this rears its ugly head.


Jag Dealership $1530 (ouch):
System vac and recharge
Checked climate control module (and swapped another CCM) - operation normal.
Replaced water pump and reservoir bypass hose (at the time I thought heater didn't work at all. Now it works on HI only)
Multi point inspection ($512 of the $1500)- lesson learned. It is 17 year old car. Shocking ;-) that the dealership would tell you that every hose, bearing, etc. looks worn).
I see in the mechanic's notes that "heat matrix flap getting stuck due to mechanical internal fault" - yet no repair was done. Since heater valve was replaced by independent, this should not still be an issue, right?


Independent mechanic (specializes in European cars. Garage full of jags. Seems genuinely helpful and is as perplexed as I am). The following has been done over the course of a few visits:
Replaced cabin air filter
Replaced A/C compressor and receiver drier ($1175)
Replaced a "lazy" solenoid
Said evaporator sensor is fine and not causing freeze-over
Said not actuator problem.
Replaced heater control valve (aka heat matrix, DCCV, I think)
I can't recall if he also did an evac and recharge. Would he have to do it with all the other work he has done?


Me:
Last weekend I replaced the climate control module. I could not find a new one available so I replaced it with one off ebay (that was taken out of service around 110,000 miles). There was no difference in the behavior of the AC. Surely two would not create the EXACT same problem.


Should I go back to square one and just replace the evap temperature sensors? Just replace them? That seems like the most logical solution. I think I could do that myself. It doesn't look too challenging. I am not super mechanical but have replaced the CCM, turn signal switch and the ashtray (door was broken).


I truly appreciate everyone's input. You can see I have spent more $ on this one issue than the value of the car. I love the car and don't really want a new one!


Best,
Kerri
I believe I should now have a signature that shows my vehicle but if not:
2000 S-Type 3.0L V6
149,000 miles (I might have hit 150,000 recently...I need to go check!)
Black Anthracite/Cashmere.