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View Full Version : Dash blowing super hot air while AC is on


viagap
08-08-2013, 09:53 PM
('04 Freightliner 3500 158")

Hi all,

My Sprinter's middle top two vents blow cold air and the rest of the vents blow extremely hot air. The AC compressor turns on and off when the AC button is pushed and the low pressure valve shows normal readings.

The issue was intermittent for a while but now the whole system is stuck blowing mixed hot and cold air. I have searched many different forums and threads, so far the issue sounds like it might be related to the "diverter" or "solenoid" valve. Nobody really mentioned how to identify or further investigate the hot air issue.

Does anyone have any suggestions on what I should check / troubleshoot next?

On a side note - I noticed the ATC temp dial goes past the normal stop points and the LED is burned out - not sure if this is related or not.


The very left heat / temp control dial does not seem to have a cable, it looks like an electronic potentiometer or thermostat.

The only dial that has cables is the center one that selects which vents blow air. The center dial is difficult to turn but the cables function and the plastic clips.

Is the center dial associated with the temp control at alll? How can I tell if the left ATC temp dial is good or not?

http://imageshack.us/a/img687/5779/t21q.jpg
http://imageshack.us/a/img10/9508/4ppp.jpg
http://imageshack.us/a/img832/2635/qor1.jpg

bc339
08-09-2013, 05:25 AM
The center control knob on the ATC positions the louvers for air distribution and also controls the Recirculation function when it is pushed in.

The temperature sensor on the ATC - between the center and a/c switch - has a small fan to draw air over it. The impellers will collect alot of dust/dirt. Very easy to clean (gently) while the face cover is removed.

The left knob is the temperature control. It controls the water valve and is powered to the closed position. Check to see if you have voltage at the valve - the valve is located on the right side above the middle of the engine (vehicle right side as facing the front). Check to see if the voltage modulates or changes as you change the temp control.

If you determine the ATC panel is the problem, you have several options for a repair.

Do it yourself - kind of difficult without a schematic. I'm looking for one now.

Have the ATC panel repaired. There are several places listed on the internet that offer climate repair service from around $80 to $130 and guarantee their work.

Replace it with a new ATC panel. New from Dodge will be a genuine Mercedes part, around $400.00. Lower priced ones ($320 range) are most likely made by Wells Vehicle Electronics.

There is a good description of the system in the service manual. If you don't have one, download it from here: http://sprinter-source.com/forum/showthread.php?t=26431

Bruce

riskydnb
08-09-2013, 08:27 AM
You need a new HVAC control module. Not only is the hot/cold knob broke but the relay is most likely compromised too, thus why it is intermittent. I have a remanufactured one for sale with a year warranty, $200 plus refundable $75 core fee. PM, call or text me @ 760.622.0148 -Randy

wires
08-09-2013, 04:37 PM
Does it only blow hot air for 5-10 minutes then go to blow cold after a hot restart? Mine does that and so does a friend's. There are (at least) two possible problems:

1. Faulty HVAC control module. Incorrect or missing PWM signal to the heater control valve can cause full heat or erratic operation. The heater is much more powerful than the AC so it overwhelms it...

2. Faulty heater control valve. Mine was jammed up and taking it apart and cleaning it cleared the problem up for a while. Sometimes rapping on the side of the heater control valve will get cold air blowing again if this is the problem.

Does anyone have a schematic of engine coolant flow on a Sprinter? I can't find one anywhere.

viagap
08-09-2013, 04:48 PM
Thanks for the quick responses! Just to confirm the "ATC panel" / "HVAC control module" / "climate control panel" are all the same part reference correct?

Is there any way that I can set the system to blow only cold while I order a replacement part?

viagap
08-09-2013, 04:53 PM
Does it only blow hot air for 5-10 minutes then go to blow cold after a hot restart? Mine does that and so does a friend's. There are (at least) two possible problems:


The vents would blow cold for 1-2 days then go back to hot for 1-2 days . Its been stuck in hot mode for a week. I haven't noticed any difference after restarting.

riskydnb
08-09-2013, 04:54 PM
Thanks for the quick responses! Just to confirm the "ATC panel" / "HVAC control module" / "climate control panel" are all the same part reference correct?

Is there any way that I can set the system to blow only cold while I order a replacement part?

HVAC control module is the 3 circle knob areas in the center of the dash. the top vents will always blow cold so you can close all vent except for those.

viagap
08-09-2013, 04:55 PM
Check to see if the voltage modulates or changes as you change the temp control.

Bruce


I'll give this a try today, thanks for the info.

viagap
08-09-2013, 05:05 PM
HVAC control module is the 3 circle knob areas in the center of the dash. the top vents will always blow cold so you can close all vent except for those.

Tried that but the heat still creeps in. I thought I would ask in case there might be one of those run a wire from point A to point B workaround fixes. :laughing:

LuckyDawgz Jim
08-09-2013, 06:26 PM
HVAC control module is the 3 circle knob areas in the center of the dash. the top vents will always blow cold so you can close all vent except for those.

On my 2002 the "top" vents over the radio are just that, fresh air vents... and not A/C related at all.

viagap
08-09-2013, 08:48 PM
I'll give this a try today, thanks for the info.

I found the water valve by looking at the service manual. (thanks for providing the link)

The voltage at the water valve connector showed 10.75 with everything off on the blue cool setting and 0 at the red heat setting. Then after I turned the blower and AC on the voltage dropped between 7.5 - 9; after turning the van on and off I noticed the voltage would fluctuate every time I started the van.

After noticing that the default is zero volts and that that the volts go up as the heat dial goes to blue -- I figured that the valve stays open when there is voltage. I proceeded to run two wires from the battery to the water valve to check whether it would make a difference to have slightly higher voltage from the battery.

After hearing a click inside the water valve cylinder, I decided turn the van on and let it run with the wires connected directly from the battery to the valve. The dash vents didn't heat up and stayed cool.

What's the correct or minimum voltage output at the valve connector? l'm assuming that it should be around 12v?

If I run the wires properly and leave connected like this for a couple days with a fuse would any other components be at risk??

http://imageshack.us/a/img7/9907/qpfa.jpg

bc339
08-10-2013, 12:23 AM
It may work for for a while, but you may end up causing the valve to wear out faster. This shouldn't damage anything else.

The signal to the valve is a PWM or a pulsed width modulation voltage.

This is the description from the service manual heating and cooling chapter:

The automatic temperature control (ATC) system controls interior temperature by taking actual values from the temperature sensors and the CAN bus and comparing them to the nominal value of the temperature control switch. The electric pulsed heater valve is then energized depending on the requested quantity of heat and an electrically-operated water pump gives a nearly constant water flow for exact temperature regulation. If the solenoid is not energized, the coolant circuit to the heat exchanger is fully open. To control the temperature the solenoid valve is pulsed by the ATC in periods of four seconds.

Unfortunately, the service manual does not state the voltage required to keep the valve closed. Based on your testing, I would say that the ATC is not working up to spec to keep the valve closed.

Bruce

wires
08-10-2013, 01:31 PM
The signal to the valve is a PWM or a pulsed width modulation voltage.

Yep. So the voltage to close the valve is 12 volts. That is how PWM works. (http://arduino.cc/en/Tutorial/PWM) The only possible danger to supplying constant current to a device designed for PWM would be that the device isn't rated for 100% duty cycle. I'm fairly sure the heater control valve on a Sprinter can handle being closed all the time.

With a constant voltage the valve won't "wear out faster" since it isn't moving. However if the valve is sticky an new ATC may not solve the problem.

Aqua Puttana
08-10-2013, 04:06 PM
... The only possible danger to supplying constant current to a device designed for PWM would be that the device isn't rated for 100% duty cycle.
...
That is not entirely true. In many PWM control schemes the system supply voltage is conditioned so that the PWM signal at the device never reaches the higher supply voltage.

As a specific example from other Sprinter PWM the glow plugs on the NCV3 come to mind. The glow plugs are PWM controlled and rated for around 5 vdc. (I'm not looking up the specific voltage.) If you jump 12 vdc to those glowplugs they will quickly burn out.

I'd research the control design closely before hitting that heat control valve with 12 volts from the battery. vic

supermoto154
08-25-2013, 07:20 PM
Is it possible that a low battery will cause heat to come out? My 2002 sprinter has this same issue, it's fine every morning but by the days end it's blowing heat. If I put it on a battery charger the A/C blows cold again??

viagap
09-19-2013, 05:26 AM
I drove with the switch and wire workaround for about 1 month / 9,500 miles. The switch was on while driving and off while parked for the night. No immediate issues have been noticed -- *yet*.

After swapping the ATC clmate control panel the issue was resolved. Thanks again to everyone for your suggestions.

bc339
09-20-2013, 03:28 AM
Thanks for the update. Was the replacement ATC panel used, new or repaired?

Bruce

viagap
10-16-2013, 08:41 PM
Thanks for the update. Was the replacement ATC panel used, new or repaired?

Bruce

The replacement ATC was used. I bought a refurbished one on eBay and got a core charge discount for sending in the broken one after.

Missouri Blue
08-24-2014, 09:15 PM
Does it only blow hot air for 5-10 minutes then go to blow cold after a hot restart? Mine does that and so does a friend's. There are (at least) two possible problems:

1. Faulty HVAC control module. Incorrect or missing PWM signal to the heater control valve can cause full heat or erratic operation. The heater is much more powerful than the AC so it overwhelms it...

2. Faulty heater control valve. Mine was jammed up and taking it apart and cleaning it cleared the problem up for a while. Sometimes rapping on the side of the heater control valve will get cold air blowing again if this is the problem.

Does anyone have a schematic of engine coolant flow on a Sprinter? I can't find one anywhere.


OK I'm reviving this old thread... if need be I can start a new thread.

I am having the problem described by "Wires" as quoted above. Here is what I have noticed:

The AC clutch engages every time I press the ac button on the ATC and disengages when I turn it off (red light off). When I first start the Sprinter the vents will not blow cold air even though the clutch is engaged. I can let the ac run for 10 minutes under these conditions and the aux fan will not turn on. Then I turn the van off and restart it and the AC begins to blow cold (and will blow cold all day) and the aux fan turns on within one minute.

If it is a faulty heater control valve why does the aux fan not turn on when the ac runs for 10 minutes (outside temp is 95 F)?

If it is a failing ATC why does the clutch engage every time?

When I change the thermostat know it works as it should.

Any help is much appreciated...

photogravity
08-24-2014, 09:51 PM
Get it repaired by this guy (http://www.ebay.com/itm/281014376808). I sent mine to him and it was sent back the same day after being repaired. Unfortunately, there was something else wrong with it and it was unrepairable so it still didn't work. They went out of their way to make me happy and ended sending me a used, but working unit to replace mine. I have no hesitation to recommend and use these guys for anything because of their service and standing behind their work. The cost is about 1/4-1/5 that of new, so you'll save plenty of cash.

Missouri Blue
08-24-2014, 10:00 PM
Does it only blow hot air for 5-10 minutes then go to blow cold after a hot restart? Mine does that and so does a friend's. There are (at least) two possible problems:

1. Faulty HVAC control module. Incorrect or missing PWM signal to the heater control valve can cause full heat or erratic operation. The heater is much more powerful than the AC so it overwhelms it...

2. Faulty heater control valve. Mine was jammed up and taking it apart and cleaning it cleared the problem up for a while. Sometimes rapping on the side of the heater control valve will get cold air blowing again if this is the problem.

Does anyone have a schematic of engine coolant flow on a Sprinter? I can't find one anywhere.


Thanks! If I was a little more sure that the ATC was the problem I'd send it off right away. I think that the aux fan is supposed to come on when the high side reaches 290 PSI.
1) Why will the ac clutch engage and run indefinitely (10 minutes) without blowing cold air and without the aux fan kicking on, but as soon as I turn off the van and restart the ac begins to blow cold and the aux fan starts up?
2) Would mixing hot air with cold air (faulty heater control valve) keep the psi on the high side of the ac down so the aux fan wouldn't be signaled to come on?

THanks for any answers to either question.

photogravity
08-24-2014, 10:49 PM
The behavior you describe in question 1 is very similar to what mine did within the last week or two before it finally failed entirely. I don't have the answer to question 2.

I have an 02 T1N and did not test to the extent you are. As far as the AC turning on the aux fan, I find that when I expect the aux fan to be on, it isn't. It seems the fan needs an extra criteria for it to turn in, I think it has to be as a certain operating temperature to turn on. The way I tested to eliminate the water cut-off valve is what viagap did above. That confirmed the valve was working and I then moved on to the ATC. I previously had the AC serviced and it checked out just fine, but it still wasn't blowing very cold air, which was noted by the mechanic at that time. I think the reason the AC wasn't very cold was because the ATC was already starting to fail when it was serviced..

In the case of my ATC, AC switch turned off and on, REST worked, aux heat worked, fan worked. Until I jumped the wire to eliminate the valve as being the issue, it just blew heat all the time no matter the position of the temperature knob, I figured I had narrowed it down sufficiently by that point.

flemsmith
08-18-2016, 07:27 PM
2004 LTV van conversion on 2500 chassis. I'm only getting cold air out of the two vents next to the center radio speaker; front dash vents sending ambient air seems like.... Started out pulling the climate control module and sending it off to be refurbished while I used teflon lube on the two cables actuated by the middle knob on the module (they were real hard to turn). Got it back, no improvementin the AC flow to the front vents, although the conrols work a lot smoother now. So I ordered a heater control valve (water valve located sorta below and behind the blower motor that feeds the cabin air filter). NO change with the new valve....I used a mirror and looked at all the wiring harness stuff around the heater valve too, (I've clearly had critters getting after the insulation on and off, so suspected a possible wiring problem) it looks fine best I can see. Now I'm stumped and getting pissed off. I'll read this thread and see if I'm missing anything, but appreciate any advice anyone has. Thanks. roy

Midwestdrifter
08-18-2016, 07:42 PM
Can you briefly clamp the coolant hose running up to the heater core? It is located in the engine compartment near the heater valve. If the air gets colder, you have a coolant flow control issue.

The heater valve needs 12V to stop the coolant flow to the heater core, if its sticking or not getting power, you will have hot air.


If you are low in refrigerant, its possible that only part of the AC core is getting cooled. I would think the drivers side vents would be colder in this case. :idunno:

flemsmith
08-18-2016, 08:27 PM
Thanks....I clamped off the middle hose feeding the heater control valve (opposite the connector), assuming that's the feed into the valve. Is that the right hose? No change.
I also took the old heater control valve, hooked 12v DC to it, and verified that it changed from allowing air flow from the middle hose described above to the bottom hose with no voltage, and that flow stops and changes to open flow between the two hoses on the same side as the connector with 12V applied. So I think I just replaced a perfectly good heater control valve. I'm beginning to wonder if there's some cable actuated flapper that is broken...?

Next I'll try running 12v directly to the connector and see if that tells me anything different. I did call the module repair guy, who says the module is tested for the correct voltage out during the repair process, although he couldn't tell me what that voltage was supposed to be, just that it should be different for AC on vs off.

Midwestdrifter
08-18-2016, 08:31 PM
There is no blend door on T1N sprinters. The heater valve performs this function. All air except the center top vents goes through the heater and AC core. The top 2 vents goes through the AC core only.

flemsmith
08-18-2016, 08:56 PM
OK, I ran 12V directly to the control valve, now I get AC air flowing thru all the vents. So I then put my little voltmeter to the connector that feeds the control valve, and I'm getting no real voltage in either the AC on or off position; there is a slight voltage difference, but it's less than 2 or 3 tenths of a volt. So either the module I just had repaired is not putting out the voltage needed by the heater valve, or I have a broken wire somewhere between. Since I do see a little bit of voltage, I suspect it's not a broken wire. great.

flemsmith
08-18-2016, 09:16 PM
Correction!!! I have 0v in both AC positions, because I have a broken (chewed by a varmint) wire. It's way up behind the fresh air cabin filter plumbing....Now I just have to figure out how to get to it. Thanks for all inputs. roy

KarlTheMechanic
08-18-2016, 10:25 PM
On my 2002 the "top" vents over the radio are just that, fresh air vents... and not A/C related at all.
Thats because you have no AC. Or, if you have, it doesn't work.
Cheers.

LuckyDawgz Jim
08-21-2016, 03:26 PM
Thats because you have no AC. Or, if you have, it doesn't work.
Cheers.

:thinking: No... my Sprinter's A/C feels like it will freeze your face off.

Seems like "Cool" air comes out of those top vents just it's just not anywhere as cold as the lower ones.

Vic stated it much better, I stand corrected:
Very normal. The top vents are completely separate from the controls on the ATC panel. The only control is the manual damper wheel on each of those vents.

They tap off after the air conditioning evaporator coil, but before the heater core. The choice is outside (ambient) air or air conditioned air if the air conditioner compressor is enabled. You will not get heat out of those vents above ambient temperature. I close mine for the winter for two reasons. First is that I don't want cold air. Second is that closing those vents will help to force more air to the defrost vents. vic