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Help, I’m ac dumb.

JohnnyCarcinogen

Active Member
Joined
Aug 3, 2019
Messages
40
Location
Missouri
Occupation
Trash Monkey
D8T waste handler chucks ice cubes at idle, operators complaining that it doesn’t AC when worked. AC had over double charge when we finally got a real robinair machine. Replaced low pressure switch. What are my next steps to **** up the operators besides “I didn’t have AC in Iraq.”?
 

heymccall

Senior Member
Joined
Feb 19, 2007
Messages
5,349
Location
White Oak, Pa
Is the evaporator clean?
Do you have refrigerant gauges?
Can you share the high and low side pressures, both at idle and rated speed?
How much charge did you install?

Care to share the serial number, or, at least the prefix? There are 8 different prefixes for D8T machines.
 
Last edited:

JohnnyCarcinogen

Active Member
Joined
Aug 3, 2019
Messages
40
Location
Missouri
Occupation
Trash Monkey
Is the evaporator clean?
Do you have refrigerant gauges?
Can you share the high and low side pressures, both at idle and rated speed?
How much charge did you install?

Care to share the serial number, or, at least the prefix? There are 8 different prefixes for D8T machines.
Evaporator is clean. I have gauges, but we’ve been too busy with other machines in the shop for me to go down to the shop and check. Machine called for 1.7 kg, so after I pulled 3.7 kg out, I recharged to the proper amount.

Prior to us getting a proper AC recovery/recycling machine, the older mechanic just added refrigerant until AC blew cold...
 

DMiller

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Feb 21, 2010
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Hermann, Missouri
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Cheap "old" Geezer
Chances are the condenser fan(s) are not running, at idle may see enough low refrigerant flow to cool Some but as speed and pressures increase heat just builds. That and filth in Both cores, Condenser and evaporator, that will retain water on the evaporator side and freeze up as soon as drops to cold enough. These do/should have filters in them that need cleaning or changed unless previous hammer head took them out for His convenience.
 

Nige

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Jun 22, 2011
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28,980
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G..G..G..Granville.........!! Fetch your cloth.
As above. Have you checked both the fresh air and recirculation filters.? I assume this machine is a waste disposal arrangement so it may even have a turbine precleaner with a third element in it. I also assume that the AC filters will be the activated charcoal version for odour control.
How about a Serial Number..?
Where is the AC condenser mounted.? Under the hood, on the RH fender, or on the cab roof..?
Might also need to dig into the dryer and/or the accumulator, but that can come later - basics first.
 

JohnnyCarcinogen

Active Member
Joined
Aug 3, 2019
Messages
40
Location
Missouri
Occupation
Trash Monkey
I'm back on the clock Tuesday. I can't promise answers then, but the dozer in question is sitting in my shop right now. The previous mechanic was old-school, the current secondary is a blonde's hair from retirement, and I'm on my second retirement. I'll lay down with proper answers and a SN.
 

JohnnyCarcinogen

Active Member
Joined
Aug 3, 2019
Messages
40
Location
Missouri
Occupation
Trash Monkey
Gauge readings are everything in a scenario like this. Under various conditions.
I won’t be back at work until Tuesday (two four day weekends a month), but the machine will be in the shop. I’ll try to update all the questions then.
 

Vetech63

Senior Member
Joined
Aug 10, 2016
Messages
6,362
Location
Oklahoma
1. Need gauge readings.
2. Notice when the blower fan is on high...……..does it sounds like a hurricane and is there a lot of air blowing through the vents.?
3. Are ALL the condenser fans on and running?
4. Does the compressor cycle electrically?...……...and how often when running?

If it is cold when you first start it up, you are probably dealing with evaporator freeze up......especially with the high humidity in the area lately.
 

56wrench

Senior Member
Joined
Dec 4, 2016
Messages
2,074
Location
alberta
I know its a stretch, but if you can get the operator to avoid running the a/c on max cold in high humidity conditions, the evaporator may not ice up. this could be a classic case of less is more.
 

DMiller

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Feb 21, 2010
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16,432
Location
Hermann, Missouri
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Cheap "old" Geezer
Generally on High Cool max air flow the systems will have a Recirc Mode for cabin air, that should eliminate the freeze potentials.
 

TVA

Senior Member
Joined
May 14, 2018
Messages
2,245
Location
USA
The nature of frost can tell you a lot: if the TXV it self is block of ice then there’s restriction there! If only part of coil frosted than its low on charge. But with construction machine I suggest everybody to start with evap. air flow! Due to nature of operating conditions cabin air flow is a main culprit!!!
 

heymccall

Senior Member
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Feb 19, 2007
Messages
5,349
Location
White Oak, Pa
I think yunz are missing that it may be a thermostatically, computer, controlled system. When I picked a random D8T in the parts manual (sonce no one provided a serial number), I saw temperature sensors in the ductwork.

Is there a digital control panel?
Knobs?
 

Birken Vogt

Charter Member
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Nov 30, 2003
Messages
5,305
Location
Grass Valley, Ca
Well if the low side gauge starts out somewhere reasonable and then goes way into the 20s and teens on the °F scale after running a while you know you have a failure of whatever part keeps the evap from freezing. You need gauges and thermometers to know what to chase first.
 

DMiller

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Feb 21, 2010
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Location
Hermann, Missouri
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Cheap "old" Geezer
Electronically controlled Solenoid/expansion systems? Or relying on a expansion orifice as so many now do?
 

JohnnyCarcinogen

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Aug 3, 2019
Messages
40
Location
Missouri
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Trash Monkey
Gentlemens, I will be at work tomorrow and, barring my shop being filled with mission critical equipment, will put gauges on the machine, get the serial number, etc.

This is how the shop looked Wednesday.


Wait, can I not upload directly from my phone? Boo!
 

JohnnyCarcinogen

Active Member
Joined
Aug 3, 2019
Messages
40
Location
Missouri
Occupation
Trash Monkey
Gentlemens, I will be at work tomorrow and, barring my shop being filled with mission critical equipment, will put gauges on the machine, get the serial number, etc.

This is how the shop looked Wednesday.

Think I figured it out
 

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heymccall

Senior Member
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Feb 19, 2007
Messages
5,349
Location
White Oak, Pa
Most of the cat excavators I've touched lately are expansion valve with a thermo probe in the evaporator. Dirt restrict air flow, evaporator gets too cold, probe opens clutch circuit.
 

JohnnyCarcinogen

Active Member
Joined
Aug 3, 2019
Messages
40
Location
Missouri
Occupation
Trash Monkey
I know its a stretch, but if you can get the operator to avoid running the a/c on max cold in high humidity conditions, the evaporator may not ice up. this could be a classic case of less is more.
I can’t get the operators to use the engine brakes on our 740Cs, which causes high brake temp codes, you really think I can talk them into using less AC? These are government workers, they start an hour late and turn in an hour early!
 
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