Another A/C Thread...

[DaveHess]

My A/C just started acting up after 12 years of ownership. It began with the airflow from the vents dropping dramatically. I made the leap that the condensor was probably iced up and there restricting airflow to the vents. I opened the hood and found the low pressure line iced up where it enters that black thing (technical term) on the firewall. Shut the A/C off and parked the truck for awhile and waited for the condensor to thaw. Ended up with a very large puddle under the truck where it normally drops water from the Air. Decided to try A/C Pro from my local parts store. Hooked the can with guage up to the low pressure side, adjusted the gauge face dial for the appropriate temperature outside and sure enough, it read low on freon. I followed the manufacturers instructions to a "T" and the gauge came up to the lowest acceptable reading on the cans gauge. I tried to get the gauge to midscale by adding more from the can but it appeared the A/C system was done accepting or the can was done delivering. Prior to adding the can (actually 1/2 can), the air was cold until the condensor froze and once it thawed, the air was cold again until it froze again. It was cold after I added the can of A/C Pro. I also watched the compressor last night. It engaged as advertised but I did not see it disengage at any time during my 30 minutes of servicing the A/C. I am pretty sure that in and of itself is the clue but not sure where to start looking. I read on other posts of a "Thermistor" on the condensor???? Can anyone please throw some ideas out here. Right now I run the A/C until I notice a diminished air flow at which time I shut the air down until the cab becomes very warm and then re-engage the A/C repeating as necessary.

 

[PWong]

Condenser was the one mounted in front of the radiator.
Evaporator was the one inside the cab that give you the cold air.
There was a evaporator temp sensor mounted to the fins of the evaporator.
This temp sensor signal was monitored by the A/C Control head.
Control head would cancel the A/C Clutch request once the evaporator temp was above to freeze.
Take the ambient temp, high side and low side readings before it freeze up.
It would tell more of the story.
The temp sensor may be defective.

 

[DaveHess]

PWong: Thank you for correcting me. It is the evaporator that is icing up. Thatnks for the tip.

 

[DaveHess]

How accessible is the temp sensor?

 

[PWong]

How accessible is the temp sensor?

Not easy. It's mounted on the evaporator. And the evaporator was mounted inside the air box. The dashboard has to come out.

 

[DaveHess]

Not what I wanted to hear....... Can a scan tool tell for sure if it is the culprit?

 

[PWong]

Not what I wanted to hear....... Can a scan tool tell for sure if it is the culprit?

Yes.
I think the connector was outside the air box.
You can just plugin a new one to test the system
Also you want hook up gauges to the system as I mentioned before to collect more info.

 

[PWong]

Here are causes of frozen evaporator:

Lack of air flow through coil with very high humidity. Fan? Dirty coil?
A low charge condition that can create a partial icing condition of the coil.
Drain plug clogged.

Again check the gauge readings.

The evaporator temp sensor was mounted in the midway from the bottom of the coil.
The freezing would start from the bottom of the coil.
So under partial icing condition of coil the temp at midway of coil may be not low enough to cycle the compressor off.

 

[Tuesdak]

These systems are charged by weight. Best way to fix it is to leak check the system. Sadly evaporator leaks - dash has to come out- are common for this truck. After leaks are fixed recover the R134A, vacuum the system, and recharge the system by weight.

The gauge numbers on this system are for diagnosing it only. With ~ 2LBS in the system the margin for error is small. Compressor oiling is compromised when this system is low on freon. Checking that the inlet and outlet temps on the evaporator are near the same is as close as you get - and that's not good enough.

You would be surprised how cheap a shop will leak check, evac, and recharge a system for you vs. the $50.00 the AC Pro already cost.

Note: The 2003's have a memo out to update (replace) and relocate the temp sensor for just this sort of freeze up condition. Run the AC on recirculate in the meantime.

 

[DaveHess]

JD, Thank you for the response. This situation occurs even in Recirc mode. I take it that makes a difference???

 

[Tuesdak]

JD, Thank you for the response. This situation occurs even in Recirc mode. I take it that makes a difference???

In this case the above conditions of being low on freon etc. make the freeze up more likely. Was the temperature lower on the driver side vents and warmer on the passenger side vents? This is a low freon condition.

Here is the sensor location memo info:
Replace the evaporator temperature sensor with part number 5140727AA

https://www.turbodieselregister.com/threads/168202-AC-Fin-Sensor-Relocation-WHERE

Also your build date may have this issue popping the relief valve on the system:

https://www.turbodieselregister.com/tdrarticles/TSB-2012.pdf

18-003-04
Poor A/C performance, slow fuel gauge response, and diagnostic trouble codes PO341 and P1757.
This bulletin applies to vehicles equipped with a Cummins Turbo Diesel engine (sales code ETC
or ETH) with an engine serial number 57130284 or earlier and the engine date of manufacture on
or before December 10, 2003. The owner of the vehicle may describe slow fuel gauge response
after adding fuel. On California emission equipped vehicles, the problem is rapid A/C clutch
cycling and poor A/C performance until coolant temperature reaches 170°. The repair involves
erasing and reprogramming the Cummins ECM with new software

 

[DaveHess]

JD the temperature feels the same between passenger and drivers side. Also this truck does not have the split system. What I like is what everyone gets! The only slow movement of the fuel gauge is at the "F". Mine generally goes a little above the "F" when full. That last couple of mm is slow going starting at just before the "F". The trucks Build date is 4/4/2003.

 

[Tuesdak]

Split system doesn't matter. Low freon makes the 'top' of the evaporator warmer and that's where the passenger air ducts get their air from. Just a symptom to help troubleshoot and that is Driver AC ducts colder than the Passenger side. After mine did this 3x over I finally found the leak - Evaporator found by 'sniffing' the AC drain and getting a hit with the leak detector.

 

[DaveHess]

And the only way into this beast is with the dash out.......... We're getting ready to go on vacation pulling the Jayco. This does not make me happy. I have an appointment for Saturday morning for a professional look at it. I wonder if given the age it would be a smart idea to have them vacuum and refill.

 

[K5IP]

DaveHess,
My 03 was also freezing up. Not wanting to take things apart to change or relocate the fin sensor, I decided to modify it. The fin sensor wires are available at connector c200 located inside the the passenger side kick panel. I cut one of the wires and added a 10K pot in series with the fin sensor. I can now set the compressor to turn off at level that prevents freezing. I could have used a fixed resistor, about 5k would have done it but I like the adjustable feature which turns the system into a variable- efficient mode.
There are still times when I want the compressor operating in the original mode (hot dry climates), so I mounted the pot in one of the cubby holes on the dash.
If you want to consider this approach (cheap and quick), The fin sensor wires are available at connector C200, cavity 9 and 10, colored LG/BK, and DB/GY. Cut the DB/GY (gnd side) wire and place the 5kfixed or 10K variable pot in series with the wire. If a fixed resistor is used add a switch in parallel with the resistor so you can revert back to the original sensor operation at will.
K5IP

 

[DaveHess]

K5 that is interesting! Dumb question.. Withe the 10K Pot, how would I figure out the setting for my system? If I decided to use the 5K ohm resistor, what could I expext to happen operationally of the compressor? And since I would basically be placing either the resistor or the Pot in line (in series), does that make the sensor inoperable? Sorry for all the questions. Just curious before I start cutting wires

BTW, thanks for jumping in here to help!

 

[Tuesdak]

Thanks as well. I would like to "warm up" the AC by cutting out the compressor sooner as well. The AC gets too cold on low fan speed during longer drives requiring me to kick the heat dial in some. Yes, there is such a thing as AC that is too cold in Arizona.

 

[K5IP]

Dave,
Not dumb at all.
Since I have made my living in electronics, what might seem easy to me, may not be.
You are not making the sensor inoperable by inserting series resistance. One way of thinking about this is that you are modifying the output of the sensor.
As you start to add series resistance, the compressor will turn off at a higher temperature.
In my case, When the pot is set for zero ohms, no temperature changes are made. When I have the pot at 10,000 ohms, (10K) the compressor hardly comes on at all. (very warm)
I came up with the 5K number by measuring where the pot is usually set, but, like in the stock market, your results may vary. (hence the potentiometer).

 

[DaveHess]

K5, Thank you again for your patience and taking the time to help me out. One more question. Does this mod work with a sensor that may be going out or only with a known good sensor?

 

[DaveHess]

JD, Thats good stuff there!