PLTW Engineering Mechanic Creeper Survey Twin Valley High School Engineering Survey:Hi, my name is Sam Rippy, and I am a senior working in an engineering team at[more ...] Posted by mroseboom 27 Feb : 09:23
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I am working on the above unit it is a 2001.As my a/c skills are just starting to develop, I need some help.Driver complaint is, not cooling properly.This unit was worked on by someone else fairly recently.Checked for leaks,condenser,compressor, etc.No apparent problems found.Clutch cycles fairly often, it stays engaged for 10-15 seconds then drops out.Unit is correctly charged.I connected clutch with continuous power and a/c blows colder,since it was about 90 degrees in the parking lot anything lower feels cold.Checked air coming from vents,ranges 68-70 degrees.Low side when clutch engaged is about 25 psi,high side is about 210.According to what I have read could it be a faulty thermostat at the evaporator.Is there anything else I should check,all suggestions welcome.Thanks
The NGV AC system uses two thermistors (inlet and outlet) and pressure transducer. These are all inputs to the Cab controller (ESC). The ESC sends a signal to AC clutch. The only way to read these signals is with Diamond Logic Builder software. The AC clutch cycle time you mentioned is not real unusual. But the cab should be colder then what you say it is. I would also pinch off the hot water lines into the heater core to rule out that. Also inspect the fresh air intake filter on pass side by windshield under small grillle with two screws attaching it to cowl tray. Put ac on fresh air and the little vent door should open. Check for filter. if you have one clean or replace as needed. If you dont have filter inspect the fins for debris and clogging. Also check cab controller for faults as not all will turn on check AC light or check elect light. Depending on software level in ESC. Faults will read with bottom line being the first line of the fault example 2023-14A-10-1 14A being active 14P being passive or previously occuring. Charge weight is critical on these but your pressures sound good when clutch is on. Thermistor issues can be a problem also so check the terminals for corrosion and pin drag. This can be a hard one to figure out without DLB software but it can be done. Im sure im forgetting something so maybe others can help out lol good luck with it.
I managed to get my hands on a workshop manual.Ok here is the update.No codes found.Replaced filter.Pinched off the heater lines.Checked the vent doors.All check out.According to the manual there is no way to check the thermistors without a diamond logic reader/computer.I am a little reluctant to change out the thermistors without knowing if they are faulty.With that said if that is the only option well that is what I will do.Still reading the manual,but will take any other suggestions.
Pin drag is testing the electrical terminals for being spread or expanded open. I use a kent moore J35616B test adapter kit. Im sure there is others but its what i have. Usually any faults with thermistors or pressure transducer will set a fault. A biased transducer is possible and no fault would be present. I wouldnt advise just changing thermisters with no faults present. If it were me I would recover the charge and see what you get out of it. Recover it a few times because the accumulator often will ice up and there will be some residual charge left. I would also pull the orifice tube and check for debris. Charge weight should be 30oz. After evacuating(30minutes)+charging measure vent temp in left vent as seen from passenger side seat. AC on Max. Set engine speed at about 1300 with steering wheel switchs, close the doors and let it run watching to see if you can the get vent temp in range. Let it run for about 20 minutes.
Here is today's update.Evacuated system,replaced orifice tube,the one I pulled out had quite a bit of junk in it.Replaced accumulator and vacuumed down the system for about 45 minutes.Recharged with 30oz refrigerant.Got the temp down to about 68 degrees.Pinched off the heater hoses and temp dropped to about 65.I checked the blend door and it operates correctly and is sealing. Is there anyway to get the temp lower than 68 without pinching the coolant lines.
"accumulator often will ice up", hey just following this thread,Sounds like a tricky one and all the bases are being covered. Quick question.. Are you saying that an iced up accumulator doesn't neccesarily mean it is restricted? you just let it thaw out and evacuate again?
What happens when you recover the charge for some reason the recovery machine(robinair) will show no pressure and indicate system is empty. However the accumulator is very cold to the touch and often has a small amount of ice or frost. I usually just pour water on it and hit the recover start button again, not sure why this occurs but it sure isnt unusual. The main point is to recover the charge completly so you know what was in it from a diagnostic standpoint.
As far as the problem truck what kind of pressures are being seen now and what is the Clutch doing now cycling still or staying on? Ambient temp? With the age of this truck I have to wonder if the evap fins are restricted with dirt and debris that is unseen. I have had to take them apart and power wash when done it usually helps a lot on these systems that are borderline. Too much oil in these systems will also inhibit there ability to cool. the oil charge is 10oz total. I once had to flush and recharge about 16 of these trucks for a company along with a bunch of other updates. Each work order had about 8 or 9 lines of repairs all paid for by Int'l. Included was retrofit Horton air fans which helped the AC in high ambients at idle speeds took about a month to do there fleet.
International has a chart for A/C diagnostics, you look up the ambiant temperature, relative humidity and it will tell you what you should expect from the vent temp and the high/low pressure range. It is a real good chart because humidity plays a big part in A/C operation, if it is 90 Degrees and no humidity, 65 degrees from the vent may be all you will get so it will keep you from bashing your head on the wall. A Good A/C man is worth his weight in gold, having all the right tools and knowing how to read them is 1/2 the battle. I once saw a guy spend all day on an A/C system that was not working well and eventually someone pointed out that most of the fins on the condensor were gone, a visual is step 1 in the International A/C training course....
Clutch is still cycling,and seems to do so from the time the a/c is turned on it may run a few second longer as it is turned on.Pressures are about 20-25 0n the low and 150-170 on the high it is real difficult to get an exact reading by the time the clutch has turned on and off the needle has not had time to settle.Ambient yesterday was about 70,how do you actually determine humidity with out some sort of gauge.To me it usually feels dry.I have seen that chart in the book,and I guess I am in range.But something is not right as the temp with a/c on should be colder on the max setting with blower full on.
The charts also are to be used with AC performance test. The performance test spells out exact conditions. Aux fan in front of condenser, hood down, fan engaged if elect or air, windows down, doors closed, thermometer in vent closest to evap, eng rpm set at 1400 or 1500, no solar loading(in bay). I would road test it and see if you think its acceptable, if it was yours would you be ok with it. If not your gonna have to dig a little deeper. the hardest ones to fix are often the ones just 10degrees off. With gauge readings that are considered ok. Sometimes its just some small things contributing to the inabilty of the unit to cool properly. Warped leaking door at the AC evap allowing heat infiltration, overcharge of oil, or dirty evaporator, are the ones that come to mind to me. How much oil did you measure out of the accumulator when you replaced it?
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