Cat D6K2 AC question

[AMBMike]

The air conditioning in the D6K2 I run (Serial # CAT00D6KAWMR00579) has been problematic this summer. On cooler days/mornings (70° F +/- 5°) the evaporator freezes about every 1-2 hours, restricting airflow. On warmer days it will barely cool, sometimes better, sometimes worse.
Here's what I have done so far.
- Replaced cabin air filters. These are regularly cleaned and replaced.
- Exposed the evaporator coil and made sure it was clean and the temp (?) sensor was embedded in the coil.
Our shop guy has checked the refrigerant pressures and says it all appears to be fine. (of course it cooled well when it was in the shop).
I should add this machine has nearly 7900 hours on the clock and the AC system has had no problems prior to this.
Any advice is welcome but please remember I know basically nothing when it comes to AC systems so plain English would be appreciated.

 

[JD955SC]

If at 7900 hours and never serviced the compressor is getting long in the tooth. A common leak site for older compressors is at the front seal.

Pressure doesn’t tell the whole story when it comes to R-134A refrigerant weight is everything.

May be a good time to replace compressor before it fails and puts metal in system. Have someone who knows what they are doing replace it and the dryer (under floor mat/floor pan).

if the compressor has started to put metal in the system then it will need a full flush out and condenser core replacement is highly advised.

also check and make sure condenser at rear of cab is clean and both fans are blowing at full speed

do not buy the can of leak stop/AC Pro at the auto parts store it will screw up your system

 

[AMBMike]

Thank you JD955SC.
So you're saying it's possible the refrigerant pressures are good and the refrigerant volume could still be low?
And if this is the case the only way to know if the volume is correct would be to evacuate the system and refill based on weight?
Trying to understand as I have zero experience with this...
Also thanks for mentioning the condenser and fans. I had forgotten to mention that I had checked those and they're clean and blowing full speed.

 

[JD955SC]

Thank you JD955SC.
So you're saying it's possible the refrigerant pressures are good and the refrigerant volume could still be low?
And if this is the case the only way to know if the volume is correct would be to evacuate the system and refill based on weight?
Trying to understand as I have zero experience with this...
Also thanks for mentioning the condenser and fans. I had forgotten to mention that I had checked those and they're clean and blowing full speed.

Exactly. We draw it out with our A/C machine which weighs the recovered refrigerant and that tells us whether we are low, correct, or high on the charge weight. Too much and she won’t cool, just like too little.

The pressures can be OK in the shop under shade, especially in the morning when it’s cooler then A/C performance falls on its face during the day.

 

[AMBMike]

Thank you again!
I'll forward this to our shop guy.

 

[AMBMike]

Another rookie question...
I think I can understand the lack of cooling if refrigerant volume is low but what about the evaporator freezing on cooler mornings?

 

[JD955SC]

The fun part (and I’m being sarcastic about fun) about A/C is finding the true cause of issues like that. From compressors not cycling properly due to a bad thermostat switch to a blockage of moisture in the system or charge issues it can take some hunting to resolve.

The dryer is supposed to be changed more if you look at Cat’s maintenance recommendation but most leave it alone till it starts giving issues. The dryer has deccaisent in it, you know like the silica gel packets that are in product boxes to absorb as much moisture as possible and once it hits its limit it can’t do more. Cat also recommends changing the dryer if you have the system open more than 30 mins.