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help diagnosing a/c

bigred1500 on Tue June 07, 2011 9:19 PM User is offline

Year: 1999
Make: caterpillar
Model: 330
Refrigerant Type: 134a
Ambient Temp: 83
Pressure Low: 25
Pressure High: 225
Country of Origin: United States

hi, I'm new here and I am trying to figure out why the a/c in the escavator I use at work doesn't cool properly...I haven't really did much a/c work but I understand the principles and concept pretty good....i have blown the cooling fins out on the condenser to make sure it's not plugged up, the fan for it is the same one for the radiator and is direct drive ( if the engine is running the fan is cooling) the a/c compressor kicks in and stays engaged it doesn't cycle, the evaporator filter has been replaced...the blower motor blows good in the cab

first thing in the morning around 7:30 am it's around 83 degrees the a/c will blow 63 degrees out of the vent, the low side reads 25 and the high side reads 225..... around noon when it's 93 the a/c will blow 70 degrees from the vent, the accumulator is sweating alot and it is 52 degrees, but i am still only getting 70 degrees out of the vents in the cab it gets warm in the cab QUICK !!! I am wondering if something is restricting the flow between the accumulator and the evaporator ?? I load trucks all day and to get to the low and high side fittings I have to pull a big skid plate off in other words it's a lot of work..

there are a few things I have been wondering...

when you charge a system out of a bulk (30 lb.) cylinder on the low side... is the cylinder supposed to be placed upside down ?? I have had some people say do it and some say don't ??

how do you tell if a compressor is weak or going out other than bearing noises ??

In my case how do I tell if the system has enough or too much refrigerant without evacuating the system ?? it is supposed to hold 1.7 kg

the company has a cylinder of 134 but the mechanic that knew a/c stuff quit so I am my only hope lol...thanks for any guidance

I have a gauge set, a vacuum pump, a vent thermometer....and wanting a recovery machine

Edited: Tue June 07, 2011 at 9:45 PM by bigred1500

HVACNY on Tue June 07, 2011 10:01 PM User is offline

The only way to tell how much is in the system is to recover the refrigerant and put the exact amount the system calls for,by weight.In your case 1.7kg.. Those pressures seem a little low for 83 ambient,i would recover and charge to spec.You really should start the troubleshooting process with the correct charge so you know for sure.When you say it gets hot real quick,is that in general.I know they have alot of plexiglass windows,but have you ever been cool in a caterpillar with a working AC? Just curious.

mk378 on Wed June 08, 2011 4:23 AM User is offline

If your "accumulator" is on the high side (technically it's a receiver then), you have a TXV system. A receiver getting cold is not normal, it means there's a blockage inside. The liquid refrigerant should stay warm (condenser outlet temperature) all the way to the TXV.

ice-n-tropics on Wed June 08, 2011 1:34 PM User is offline

What is the high side pressure at afternoon ambient? If the compressor pumps 300 psi it's OK. If 225 psi confidence is 90% it's OK.
CAT typically uses both an accumulator (in the suction line) usually without desiccant plus a liquid line horizontal drier with desiccant (in the liquid line). The orifice tube is located in the drier outlet.
CAT typically pressurizes the cab with 30 to 50% outside air which results in about 70 degree air with 50 degree refrigerant.
If you can rig much less outside air the louver temp could be 10 degrees lower.
If the accumulator is sweating, the charge amount is close to right.
Be sure the heater hose lines do not flow hot water. There is a hot water shut off valve which is intended as a 100% shut off if fully activated.
If the CAT has seen a compressor change, the oil quantity may be sooo high that the air temperature will not be optimum.

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

Edited: Wed June 08, 2011 at 2:39 PM by ice-n-tropics

bigred1500 on Wed June 08, 2011 6:32 PM User is offline

thanks for the info, the accumulator is sweating good, but checking the pressures in the afternoon is just about impossible because Soon as I load a truck, another one pulls a weak compressor wouldn't show 200 plus on the high side ?? just trying to understand how to tell a bad or weak one even if mine is ok....

the answer to the have you ever been cool in a caterpillar escavator, there was a 320 cat at work I was in and it had no freon in it so I vacuumed it down and found a leak at the dryer, I fixed it and charged it up ( by using my vent thermometer and manifold gauges) i know not the best way but it blows 40 degrees out of the vent all day long, ever since then I have been interested in a/c systems....

can anyone tell me about the bulk 134 cylinders if you are supposed to turn them upside down when charging on the low side with an orifice tube system ( the service ports are on the back of the compressor both high and low)...

Edited: Wed June 08, 2011 at 6:33 PM by bigred1500

iceman2555 on Wed June 08, 2011 11:55 PM User is offlineView users profile

The charge can should be in the up right position. This will allow a 'gas' charge. Inverting the cylinder will result in a liquid charge, which may result in compressor damage.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

chris142 on Fri June 10, 2011 12:39 AM User is offline

Have you tried pinching off the heater hoses?

bigred1500 on Mon June 13, 2011 6:15 PM User is offline

I have an update, the system has a dryer in-line on the low side right before the evaporator one side was 112 degrees, the other side of the dryer which has the orifice tube in it was measuring 72 degrees ( the dryer is under the cab as the line exits it goes to the evaporator)....the weird thing is the vent would only blow 75 degrees , but as the 134 exits the evaporator it goes to an accumulator which reads 41 degrees and is sweating like my question is what could be allowing the 134 not to read 41 in the evaporator but it does after it ?? I found a flow diagram a book and will put an example below... the temp was 92 outside and the low side read 35 and the high side read 240....any thoughts ??? the heater valve is working we pinched the lines off and it didn't change one bit ( it's a ball valve on the engine)

compressor----------condenser----------dryer/orifice --------evaporator--------accumulator-----compressor

bigred1500 on Tue June 14, 2011 6:31 PM User is offline

replaced the dryer and now the inlet and outlet for the evaporator are 45 degrees but still blowing 58-60 out of the vent, the current mechanic had a buddy of his come recover the 134 the deal was he got to keep the 134 he pulled after the evac we vacuumed it down for 20 minutes it was in 28" of vacuum and then we closed the valves and let it sit for another 30 minutes with no change, so then I put 3.85 lbs of 134 in like it calls for, actually a touch more for what you lose in the hoses....what I can't figure out is how the vent temp can be 15 degrees warmer than the evaporator even though the air travels about 4 ft from the evaporate before it comes out of the vent...

I took apart the evaporator housing and the evaporator is not plugged up but is a little dusty....all the gaskets on the box and duct pieces that go into the box are mentioned before the heater core valve is off... pressures were low 30 and high 250 it was 92 degrees outside...

Edited: Tue June 14, 2011 at 6:44 PM by bigred1500

bromodragonfly on Sat June 18, 2011 8:44 PM User is offlineView users profile

Hmm. Well, 112 degree liquid line at 240psig high-side indicates that the condenser is subcooling by ~30 degrees F, which may or may not be high for automotive AC, I'm not sure. But I would assume that the state of refrigerant at that point is 100% liquid.

Low side pressure of 30psig should indicate a saturated temperature of 35F going into the evaporator. You're stating that the line temperature at the inlet of the evaporator is 45F, which is strange. The fact that the temperature drops lower in the accumulator suggests that there is still liquid coming out of the evaporator, boiling inside the accumulator, and absorbing heat.

Have you tried replacing the orifice specifically?

Other than that, has someone made repairs to the evaporator in the past? Perhaps it had a leak and someone has brazed some circuits closed? Or has it been replaced with one of smaller size?

There is no knowledge that is not power

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