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A/C Issues? Anyone else

2019_Ram said:
After having the AC TSB done early this year, I was still not happy with the AC performance. While better than pre-TSB, I am still seeing a low of 50* driver's center vent and 46* passenger's center vent. On a 90*+ day, the truck meets specs, but on a 70-80* day it does not, as I see the same vent temps. Specs are 45* on a 70-80* day and 55* on a 90*+ day, with all temps taken from the Driver's side center panel vent.

I recently took the truck to a different dealer for a second opinion, and the tech ran through all the checks and it passed everything except the vent temps on cooler days. They did provide me a bit more information than I had previously gotten, such as the lowest recorded temp of the evap temp sensor of 38*. In the next few days, I decided to look on my own some more, mainly to see if I could verify if the evap temp sensor was really reading 38*. I borrowed a DVM with a quick reading temp probe and attached it to the low side line coming out of the evaporator (as close as possible) on the engine side of the firewall. What I saw has me very confident in a theory...
  • These observations are after the initial cooldown of the system, when the compressor starts cycling. This was also done with MAX AC on. This is very repeatable, at least on my truck.
  • The lowest recorded temp I see on the line is right at 38*, this corresponds directly to the 38* referenced by the tech.
  • Every time I saw 38*, the compressor cycled off.
  • The line temp quickly rose to 44*.
  • Every time I saw 44*, the compressor cycled on.
  • This ON-ON cycle happened between 10-15 seconds. I could easily hear the ON click of the compressor.
  • When the temperature was dropping, at 39* it seemed to drop slower than at other temperatures. It seemed to take longer to drop from 39* to 38*, than from 41* to 40*.
    • I think this is where the H-Block\TXV was beginning to meter refrigerant...

This leads me to my theory. I believe the evap temp sensor is cycling the compressor based on a software setpoint of 38*. I believe this value is set artificially high, thus not allowing the H-Block\TXV time to properly adjust and meter the refrigerant. In everything I know and have researched about this, I believe the H-Block\TXV should be able to sufficiently meter refrigerant flow under a high cooling load without freezing up the evaporator. Therefore the evap temp sensor cutting the compressor out at 38* is greatly reducing the cooling ability of the system. The evap temp sensor should only be cutting the compressor out under lower cooling loads, when the evaporator is actually at risk of freezing up.

My belief is that if the evap temp sensor cutout was set lower, say to 34*, the H-Block\TXV may now have enough time to properly meter the refrigerant before the compressor is forced to cycle. The other possibility is the H-Block\TXV was not properly spec'ed, or had a defect in manufacturing, for the 38* evap temp sensor cutout and does not function at the proper setpoint.

If the evap temp sensor cutout temp was dropped to 34* and the H-Block\TXV did regulate the evap temperature at 36-38*, the compressor would no longer cycle and greatly increase the cooling ability of the system. By having the compressor run continuously under a high cooling load, I could see this reducing vent temps by at least 6*. This would put both of my vent temps under spec at all outside temps with nothing more than a slight software change.

If anyone wants to replicate this experiment, I would be happy to hear the results. See if others are experiencing the same compressor cycling as I am and see if this is part of the poor cooling performance puzzle too many of us are struggling with.
Click to expand...

Can you adjust that value from 38* to 34* in Alpha OBD?
 
gimmie11s said:
Can you adjust that value from 38* to 34* in Alpha OBD?
Click to expand...

2019_Ram said:
After having the AC TSB done early this year, I was still not happy with the AC performance. While better than pre-TSB, I am still seeing a low of 50* driver's center vent and 46* passenger's center vent. On a 90*+ day, the truck meets specs, but on a 70-80* day it does not, as I see the same vent temps. Specs are 45* on a 70-80* day and 55* on a 90*+ day, with all temps taken from the Driver's side center panel vent.

I recently took the truck to a different dealer for a second opinion, and the tech ran through all the checks and it passed everything except the vent temps on cooler days. They did provide me a bit more information than I had previously gotten, such as the lowest recorded temp of the evap temp sensor of 38*. In the next few days, I decided to look on my own some more, mainly to see if I could verify if the evap temp sensor was really reading 38*. I borrowed a DVM with a quick reading temp probe and attached it to the low side line coming out of the evaporator (as close as possible) on the engine side of the firewall. What I saw has me very confident in a theory...
  • These observations are after the initial cooldown of the system, when the compressor starts cycling. This was also done with MAX AC on. This is very repeatable, at least on my truck.
  • The lowest recorded temp I see on the line is right at 38*, this corresponds directly to the 38* referenced by the tech.
  • Every time I saw 38*, the compressor cycled off.
  • The line temp quickly rose to 44*.
  • Every time I saw 44*, the compressor cycled on.
  • This ON-ON cycle happened between 10-15 seconds. I could easily hear the ON click of the compressor.
  • When the temperature was dropping, at 39* it seemed to drop slower than at other temperatures. It seemed to take longer to drop from 39* to 38*, than from 41* to 40*.
    • I think this is where the H-Block\TXV was beginning to meter refrigerant...

This leads me to my theory. I believe the evap temp sensor is cycling the compressor based on a software setpoint of 38*. I believe this value is set artificially high, thus not allowing the H-Block\TXV time to properly adjust and meter the refrigerant. In everything I know and have researched about this, I believe the H-Block\TXV should be able to sufficiently meter refrigerant flow under a high cooling load without freezing up the evaporator. Therefore the evap temp sensor cutting the compressor out at 38* is greatly reducing the cooling ability of the system. The evap temp sensor should only be cutting the compressor out under lower cooling loads, when the evaporator is actually at risk of freezing up.

My belief is that if the evap temp sensor cutout was set lower, say to 34*, the H-Block\TXV may now have enough time to properly meter the refrigerant before the compressor is forced to cycle. The other possibility is the H-Block\TXV was not properly spec'ed, or had a defect in manufacturing, for the 38* evap temp sensor cutout and does not function at the proper setpoint.

If the evap temp sensor cutout temp was dropped to 34* and the H-Block\TXV did regulate the evap temperature at 36-38*, the compressor would no longer cycle and greatly increase the cooling ability of the system. By having the compressor run continuously under a high cooling load, I could see this reducing vent temps by at least 6*. This would put both of my vent temps under spec at all outside temps with nothing more than a slight software change.

If anyone wants to replicate this experiment, I would be happy to hear the results. See if others are experiencing the same compressor cycling as I am and see if this is part of the poor cooling performance puzzle too many of us are struggling with.
Click to expand...
This is disheartening since my truck is in the shop right now for the AC TSB...
 
diablo82 said:
This is disheartening since my truck is in the shop right now for the AC TSB...
Click to expand...
I’m considering mentioning it to my dealer, can you keep us updated to the performance of the fix once you get it back?
 
flan said:
I’m considering mentioning it to my dealer, can you keep us updated to the performance of the fix once you get it back?
Click to expand...
Will do. I am expecting to have my truck back on Thursday and temp here would be in the 90s for testing/comparing (VA/NC here).
 
All - Finally got my truck back today. The truck was in the shop for total of 8 days including weekend. So far interior wise no scratch and everything seem solid and no rattling (I intentionally drive on a road with rough pavement). Somehow they took off the wheel well on the passenger side for this AC fix and I think they actually did the work without taking the entire front dash out. May be someone can verified that.
Cooling performance wise it is great. With 90 degree outside, it took the AC with fan full blast 3 mins to cool down to 68 degree. After that the fan just went min./normal speed the entire way back included stopping at a drive thru during lunch hour.
Overall I am really satisfied with the repair. I did the hose clamp and it did get me through last summer but now I am glad that I have a fully functioned AC without thinking about how hot would it be when sitting in the traffic.
 
diablo82 said:
Somehow they took off the wheel well on the passenger side for this AC fix and I think they actually did the work without taking the entire front dash out. May be someone can verified that.
Click to expand...
I can verify that it is impossible to remove the HVAC housing and distribution box from the truck without removing the dash. If the dash wasn’t removed, those two parts from the TSB weren’t replaced.
 
If anyone else gets this done, you should put some stickers/paint or something over screws for an indicator that it was actually removed.
 
Diablo, Do you have a thermometer you can stick in your vent to see what temp air is now being produced?
 
Ok that’s an improvement over mine. I see 54 driving on the highway when it’s about 85 out. Also not much condensation out the drain compared to other vehicles in the family.
 
This may sounds funny but the fix also bring back the new car smell plus coolant.
 
So far everyone that’s had the tsb done says the same about the coolant smell. It goes away after a bit.
 
Well to be clear the idling temp showing was after a 20 mins drive.
 
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