ISO solution to recharging AC often due to Ram's ECM defect opening the AC relief

[Tuesdak]

Suddenly 2x a year my AC quits blowing cold on the passenger side on my 2003 Dodge Diesel. I have gone the Heater Treater route, replaced the evaporator that wasn't leaking and finally with dye noticed the relief valve on the compressor is venting 1/2 the system charge. Replaced the high side sensor and still blows down the system. I found out it's a design defect in 2003-2007.5 Dodge Ram pickups. I reference some extensive posts on the issue that had the ear of the engineers back in the day. My heartfelt thanks to those involved, but, the engineers simply missed the boat. SPLASH!

Your symptoms will be suddenly one day driver's side is colder than the warm passenger side, no leaks found, and the system is missing 1/2 it's charge needing an evac and recharge adding 1 LB of R134a. The 1 LB of R134a went out the high side relief valve due to a design defect in combo with the following stars and moons lined up.

Here is what happens.
1) Due to extensive research on Trailblazer SS Electro Viscous fans I found and documented that the ECM did not send control pulses to the fan clutch 2 min after startup no matter what the AC tables, AC Pressure, and ECT were doing or calling for. AC Pressure ran away till it cut out and ECT would simply rise during the timer 2 min after engine start. (My work resulted in a thicker aftermarket radiator design for the TBSS.) The Dodge diesel pickups in question have a similar computer controlled fan clutch. So you have a window of some sort where the ECM doesn't attempt to bring the fan speed up no matter how hot the condenser is getting. I submit this is a educated guess as I haven't watched or logged the fan % desired during a cold start on my truck. I guarantee you the fan isn't coming on cold.

2) It's intermittent. This means the engineers couldn't find it and cure it.
The AC system doesn't overheat and blow the relief valve at 450-500 PSI every time you do a cold start. Why? The Fan clutch is misunderstood and overlooked for most AC repairs. Regardless when you start your truck most times you get a "roar" of the fan that is locked up and it takes a couple min to unlock. (This is called Morning Sickness and all fan clutches have it. Could be it was locked up on shutdown or due to shutdown position the working fluid flowed back to the working chamber to lock it up. Regardless most times you start a cold vehicle the fan comes on with a roar till it unlocks.) IMO Morning Sickness is why there is a lock out to keep the ECM from messing with the fan clutch that's cold. The rare time that the fan clutch isn't locked up when you start the engine and then turn the AC on high is when the condenser overheats and pops the relief valve open. Our system depends on Morning Sickness from the fan clutch to not overheat and vent the AC system. Lack of condenser airflow = overheated condenser that raises the pressure to extreme levels = relief valve opening before something explodes. I do not know the exact reason the Fan clutch OEM and Dodge OEM decided to cut control to the fan during Morning Sickness. However a fan that is 100% locked up hitting an on ramp at max engine RPM sucks power and can slip the belt. I suggest they are trying to avoid a situation like this or establish control of the fan with a warm up timer.

3) The ECM has a bug and for this discussion "isn't paying attention" to AC pressures.
The AC compressor should cut out before the relief valve opens. I have no idea if this cut out is actually built into the ECM or if it just controls the fan from the high side sensor. From the TSB for CA emissions trucks I suggest it does, but, during the cold warm up and 2 min fan control lock out it's not enabled, buggy, or simply doesn't work. Thus the ECM doesn't kick out the AC compressor when the high side reaches 450 - 500 PSI at least during the cold warm up. Even when the relief valve opens the compressor is still running! There goes 1/2 the system charge!

Cure. I'll be the first in line with good money for a cure. Here are some suggestions:

1) Geno's here is your opportunity to make and sell a "kit" that cut the compressor out at 450 PSI.
A) Contact the manufacturer of the AC high side sensor add some pins and a switch to it that opens a switch at 450 PSI. Include the wiring harness and plugs to plug into the compressor coil circuit. In other words at 450 PSI switch opens and AC clutch cuts out.
B) Make a T fitting and add a separate pressure switch that does the same cut out of the compressor clutch coil. After all the pressure sensor is expensive.

2) Bring on the fan manually. KISS. Make a black box that gives you 30% PWM signal to the fan control wires after startup and when the AC is on. Include connectors to tap the compressor coil wire to sense AC is on and tap into the fan plug. This is a better solution for Phoenix, AZ where you need the AC running on a cold engine.

3) Run the EPA up FCA's six. ACGate... The defective AC system design is allowing excessive R134a venting to the atmosphere through the relief valve. Only FCA can correct this ECM software defect. Not likely to happen.

4) Wait to turn the AC on or monitor the high side pressure during a cold start with low fan speeds. You will remember to do this when it's 120 degrees out right?

Caught in the act and shut off before the AC vented. Note MAX readings with low ECT after startup. Yes, it is 100 degrees out so the engine is that hot on cold start.

References:
Engineer involved trying many things including bigger orface tube from later years that makes idle performance worse, etc.
https://www.dieseltruckresource.com...years-101/03-ac-not-working-pass-side-106452/


A solution to cool the condenser with an electric fan - IMO a electric fan is a restriction when towing and you need 100% fan. It isn't 100% as they still vent the system - just not as often. This may work for you or help.
https://www.dieseltruckresource.com...passenger-vents-not-cold-drivers-side-245620/

TSB: On California emission equipped vehicles (sales code NAE); rapid A/C clutch cycling and poor A/C performance until coolant temperatures reach 76.6° C. (170° F.)
http://dodgeram.info/tsb/2004/18-003-04.htm

 

[BILTIT]

I spoke with brian at smarty and he said with the new software (UDC Pro) there is a table that you can adjust for the fan on. One member of a site said he has his fan run 40% on anything below 1000rpm i think it was. This should fix the problem, i may attempt it later this year. I am still trying to understand the switch to UDC pro and what is required etc.


So in short, the fix may be at your fingertips and wont cost you anything but a little time.

 

[cerberusiam]

Yes, UDC Pro allows a lot of fiddling with the controls and the fan is one. To use UDC Pro you will need to buy Smarty Touch and a dongle, the software is free to download but will only load if the dongle is there. The next additional piece that will make live so much better is the comm module so you can do real time tuning as you roll down the road. It will be comparable with HP Tuners and EFI with a switch, around $1500 for the full setup, but, only thing limiting you at that point is your imagination.

 

[Tuesdak]

Hats off to Brian. He is the sole reason for my choice of the hardware in the screenshot. He has indicated they can't correct a BUG in the software say if the ECM is ignoring lookup tables during a cold startup. Other rides like I mentioned had this exact same issue of a 2 min timer preventing fan PWM pulses being sent although the tables were calling for *more* fan. Being GM it had a mechanical high side cut out switch on the AC so it didn't vent the system.

Someone would have to test UDC during this exact cold start situation. Maybe there is a table that has zeros in it for fan control during low ECT that UDC can touch.

 

[BILTIT]

Yes, UDC Pro allows a lot of fiddling with the controls and the fan is one. To use UDC Pro you will need to buy Smarty Touch and a dongle, the software is free to download but will only load if the dongle is there. The next additional piece that will make live so much better is the comm module so you can do real time tuning as you roll down the road. It will be comparable with HP Tuners and EFI with a switch, around $1500 for the full setup, but, only thing limiting you at that point is your imagination.

I thought we didn't need a dongle with the new software? I already have the Touch.

 

[cerberusiam]

I thought we didn't need a dongle with the new software? I already have the Touch.

You have to have the dongle to do custom programming.

 

[sag2]

I was not aware of any trucks that had the problem after the flash was done.

 

[Tuesdak]

I was not aware of any trucks that had the problem after the flash was done.

Did they only fix CA emissions trucks per the TSB noted above or am I missing a flash?

 

[sag2]

It mentions CA only but I would have them check yours for a potential flash. Might be good to flash over your current flash anyway.

 

[Tuesdak]

After watching the gauges over our extreme summer hot weather, 117+ degrees, I find there is a very narrow window after startup that this high pressure spike occurs. It's always with no engine fan running. I find that using a blower speed of 1 or 2 allows the engine fan to come up to speed without blowing the AC pressure relief valve. Not what you want to do in this weather, but, it works. (Lower fan speed means less AC heat load.) Best I can tell this is a 30 second or less window that the pressure spikes. When I hear the engine fan come up to speed I then can turn the blower fan on high without excessive AC high side pressure.

 

[Oz_Ram]

After watching the gauges over our extreme summer hot weather, 117+ degrees, I find there is a very narrow window after startup that this high pressure spike occurs. It's always with no engine fan running. I find that using a blower speed of 1 or 2 allows the engine fan to come up to speed without blowing the AC pressure relief valve. Not what you want to do in this weather, but, it works. (Lower fan speed means less AC heat load.) Best I can tell this is a 30 second or less window that the pressure spikes. When I hear the engine fan come up to speed I then can turn the blower fan on high without excessive AC high side pressure.

Quick question:
What about if you start driving say within 10 seconds of startup when ambient temps are >100F to get airflow over the condenser?

 

[Tuesdak]

Quick question:
What about if you start driving say within 10 seconds of startup when ambient temps are >100F to get airflow over the condenser?

I have not noted this situation yet with the PSI readings let alone experimented with lower blower speed settings after takeoff. From past experience driving immediately after startup is when I get the no cooling on the passenger side 2 miles later and have to recharge the system. IMO The time the over pressure happens is too short to allow you to get up to speed that ram air is cooling the condenser. Further RPM's needed to gain speed increase AC pressure. Usually I hear the fan come on in about 1 residential block @ 25 MPH.

 

[Prairie Dog]

Truly not trying to be a smart-ars, just trying to understand - but why have I not had a problem with this on my 15 y/o, 108K mile truck?
Although I do admit that this year, for the first time ever, I've had my evaporator freeze up twice but hasn't done it in a month.

 

[petersonj]

just trying to understand - but why have I not had a problem with this on my 15 y/o, 108K mile truck?

I think JDoremire is saying the event is a rare occurrence and if the event does occur it will likely go by unnoticed. It takes very specific conditions for the event to occur.

The following is my response to a post from a previous JDoremire thread (note the extremely high discharge pressure on a 55 degree day):

"I recently purchased a used Snapon refrigerant recovery machine for use on my own vehicles. A few days ago I hooked my sister's 2003 Ram to the machine to recover and weigh the refrigerant. Her vehicle was showing the symptoms of warmer air on passenger side by 20 degrees. The ambient temperature was 55 degrees when I hooked up the gauges.

I wanted to check the AC performance before I began the recovery process. The truck had been shut off for about two hours. When I started the engine with gauges hooked up and AC turned on, the first thing I noticed was that the high pressure side rapidly climbed to 400 psi. I shut the engine off immediately. I restarted the engine and the same thing occurred. I noticed that the engine fan was barely turning.

I recovered the refrigerant (18 oz.) and leak tested the system (passed). I recharged with 32 oz which resolved the difference in vent temperatures. The pressure situation on the high side never occurred again and I now know why.

So, with your help I now have a much better understanding of the AC problems for this era of truck and I can make a better decision about specific repairs knowing what they will or will not fix."

I would have never picked up on this if I hadn't read the recommended reads from JDoremire. I was very fortunate to witness what JDoremire is talking about. Also, my sister had not complained about the performance of the AC, I had noted the difference in vent temperatures with a thermometer about a month before I performed the refrigerant recharge.

- John

 

[Tuesdak]

Truly not trying to be a smart-ars, just trying to understand - but why have I not had a problem with this on my 15 y/o, 108K mile truck?
Although I do admit that this year, for the first time ever, I've had my evaporator freeze up twice but hasn't done it in a month.

I will attempt to help with the questions. First Dodge has you move the probe in the evaporator to prevent the freeze up. Mine did this on outside air at times so the PO said to run it on Max. I moved the probe with a heater treater door install with new Mopar evap and heater core and it did solve the problem.

I suggest yours hasn't had the problem due to mild weather you get. For example today it's currently 71 degrees where you are at, 84 degrees where the member "Spooler" from the other site is at, and 97 degrees here in AZ where I am at. The high of the day will be 104 and 122 is not out of the question for me.

The higher the outside temperature is the less cooling you get on the condenser per CFM of air flow, the higher the pressure is, and the more load you give the AC from higher cab temps. The blower (evaporator) fan speed somewhat regulates the AC load, but, the starting temp of the condenser makes a big difference. At 75 degrees cold start the pressure is 78.8 PSI. At 85 its 95.4 PSI. At 115 It's 159 PSI - double the starting pressure of 75 degrees and that eliminates headroom before the valve pops at 450-500 PSI. So for the same time to get the fan on in different weather can be the difference between a high pressure spike and blowing the relief valve. I suggest you don't start the AC on high blower settings with milder summer weather thus less load on the AC system as I noted helps keep the high side pressure down. As an aside my system can run at 400 PSI at extended idle: somewhere between 180-190 degrees. Raising the engine idle will drop the high side pressure as long as the fan is locked in somewhat. (I wish 2003 was high idle compatible.)

Even if you have traveled to hot climates it's still the random time your fan clutch doesn't have "morning sickness" from being locked in before shutdown or stopping position allowing silicone fluid drainback to lock the fan up some on startup. Most times the fan has morning sickness. Thus it takes a perfect storm to blow the relief valve. Different climates run the AC more often (I run mine year around including December.) adding to the odds they win the blow the relief valve lottery. (Winterizing a vehicle here means an AC system checkup! ) The last part is not kicking off the compressor during the cold start when the PSI gets excessive: the true ECM bug hidden by the somewhat rare perfect storm. The engineers sitting in a snowbank have neglected good AC systems running the obsolete R12 orface tube design long past it's best if used by date on R134a. Even alternate refrigerant doesn't solve the random lack of airflow on a overheating condenser. Others do experience this including one member on the TDR while his AC system was being charged making them wonder if the orface tube was clogged. Then it behaved perfectly making them scratch their heads. Edit said member posted above this post.

Further info on AC systems and the downsides of the FOT system we have is from an interview with one of the 1950's designers of the FOT system and his VOV, Varable Orface Valve, improvement. (Not available for our Dodge Ram Trucks). This can explain in depth, for one thing, the weirdness of why the high side pressures are so high at idle, but, lower at road speed's higher engine RPM with the fixed orface tube system. http://www.imcool.com/articles/aircondition/VOV1.htm

 

[Prairie Dog]

I will attempt to help with the questions. First Dodge has you move the probe in the evaporator to prevent the freeze up. Mine did this on outside air at times so the PO said to run it on Max. I moved the probe with a heater treater door install with new Mopar evap and heater core and it did solve the problem.

I suggest yours hasn't had the problem due to mild weather you get. For example today it's currently 71 degrees where you are at, 84 degrees where the member "Spooler" from the other site is at, and 97 degrees here in AZ where I am at. The high of the day will be 104 and 122 is not out of the question for me.

The higher the outside temperature is the less cooling you get on the condenser per CFM of air flow, the higher the pressure is, and the more load you give the AC from higher cab temps. The blower (evaporator) fan speed somewhat regulates the AC load, but, the starting temp of the condenser makes a big difference. At 75 degrees cold start the pressure is 78.8 PSI. At 85 its 95.4 PSI. At 115 It's 159 PSI - double the starting pressure of 75 degrees and that eliminates headroom before the valve pops at 450-500 PSI. So for the same time to get the fan on in different weather can be the difference between a high pressure spike and blowing the relief valve. I suggest you don't start the AC on high blower settings with milder summer weather thus less load on the AC system as I noted helps keep the high side pressure down. As an aside my system can run at 400 PSI at extended idle: somewhere between 180-190 degrees. Raising the engine idle will drop the high side pressure as long as the fan is locked in somewhat. (I wish 2003 was high idle compatible.)

Even if you have traveled to hot climates it's still the random time your fan clutch doesn't have "morning sickness" from being locked in before shutdown or stopping position allowing silicone fluid drainback to lock the fan up some on startup. Most times the fan has morning sickness. Thus it takes a perfect storm to blow the relief valve. Different climates run the AC more often (I run mine year around including December.) adding to the odds they win the blow the relief valve lottery. (Winterizing a vehicle here means an AC system checkup! ) The last part is not kicking off the compressor during the cold start when the PSI gets excessive: the true ECM bug hidden by the somewhat rare perfect storm. The engineers sitting in a snowbank have neglected good AC systems running the obsolete R12 orface tube design long past it's best if used by date on R134a. Even alternate refrigerant doesn't solve the random lack of airflow on a overheating condenser. Others do experience this including one member on the TDR while his AC system was being charged making them wonder if the orface tube was clogged. Then it behaved perfectly making them scratch their heads. Edit said member posted above this post.

Further info on AC systems and the downsides of the FOT system we have is from an interview with one of the 1950's designers of the FOT system and his VOV, Varable Orface Valve, improvement. (Not available for our Dodge Ram Trucks). This can explain in depth, for one thing, the weirdness of why the high side pressures are so high at idle, but, lower at road speed's higher engine RPM with the fixed orface tube system. http://www.imcool.com/articles/aircondition/VOV1.htm

Thank you for making taking so much effort to explain all that and for the helpful suggestions. It all makes sense.
I'm thinking that as soon as I don't hear the fan roar in the mornings, it may be time to replace it regardless or any other symptoms. I'll also stop cranking the fan to max. when I start it in high temps. Moving the sensor would be great but an awfull lot of work. I''ve started using the Recirc. mode more and will do that a lot more often to keep freeze up fro happening.

Thanks again,
Scott

 

[BILTIT]

I experience very high ac pressures on startup alot. I always turn off my ac before shutting down the engine or else it will see 400-450psi most times. We dont have super hot temps up here so it is mostly due to the cold start and lack of air flow.

 

[Prairie Dog]

I experience very high ac pressures on startup alot. I always turn off my ac before shutting down the engine or else it will see 400-450psi most times. We dont have super hot temps up here so it is mostly due to the cold start and lack of air flow.

I do this as well just to dry out the evaporator so it doesn't get musty. I had no idea I was helping to protect it against high pressure at start up as well.
Thanks for the info.

 

[Oz_Ram]

I always turn off my ac before shutting down the engine

I try to remember to do this too. It isn't helped by the AC switch being a 'soft' switch so if you forget, you can't switch it off unless it starts up again first.

 

[Tuesdak]

I stand corrected about extreme heat being a factor at all. If I idle the truck cold on 75 degree days like we have now I can still get 450 PSI on the high side. Further watching the fan % commanded to 99% at idle the fan is doing a lot of NOTHING for a LONG time. The only thing that matters is the fan isn't kicking in from around 250PSI to 450+ PSI. Specifically seeing less than 400 RPM on the fan.