Engine Size: 3126 cat
Refrigerant Type: r134a
Ambient Temp: 85
Pressure Low: 35
Pressure High: 220
Country of Origin: United States
getting tired of the "we fixed it" and a large bill then sweating my arse off so im trying to diagnose the issue my self, kind intimidating but im hoping i can get close to the problem,,
its 85 to 90 ambient, the vent temp is 68* i bought a set of gauges and took a reading , truck is at temp, ac on high, fan cycling, the compressor on and off im assuming normal , the reading drops when the fan kicks in low side 28 high side 150 not sure where to go , the last ac guy put die in and recovered the r134a, , i couldnt find any leaks with the uv lite
decided to double ck the numbers , with fan clutch off low side reads 32 high side 275 , the fan then kicks on and high side drops to 150 and holds there, low side drops to 20 and slowly rises to 32 and holds there, vent temp never gets cooler then 68*
Pressures look fairly good, high side kind of low like maybe undercharged a bit though. Is the low side line under the hood getting cold? Do you have the water valves to the heater turned off?
If compressor is cycling on and off in a condition like this, that usually means the evaporator core is good and cold. Or the thermostat is bad and turning it off prematurely.
Edited: Wed June 01, 2011 at 10:12 PM by mk378
the low side line is cold has some condensation but looks normal I did not pinch the heater line to see if it helps, i did manually move the valve to closed but it could be leaking past the valve
the heater water line valve seems cheap and kind of sloppy , also hard to switch from the cab
With the heater shut down, heater hoses should not be warm or hot. The vent temperature should be close to the suction line temperature.
would it hurt to pinch this line closed temporarily
to see if vent temps lower?
suction line temp?? sorry new to this ,, where is this and how can i get a temp reading to compare?
The suction line is the low side line between the evaporator and the compressor. Ideally put a thermocouple on a metal part of it to measure temperature.
got it,,, i have a remote infrared temp sensor for cylinder head readings not sure about the ability to read lowtemps but ill ck that ,, so it should match up with the dial temp gauge i have in the vent at 68*?
I hope it is colder than 68. That would show it's not a refrigeration problem, it's an issue with reheating or airflow in the cab side system.
ok did the infared test and 71 at the vent 45 at the suction line so its getting something done to be cold ,
the heater line temps are 130ish on one line into the cab and 85 on the line where the valve is
Clamp off the heater lines and see if vent temp improves. If that's the problem, get a couple of good valves for the block so you can shut heat down fully in the summertime.
do u think ill overheat the engine by closing these two lines into the cab? this should not effect coolant flow
ill look for shut offs and try a tempory clamp
Most of the big trucks I've seen have handwheel valves as the fitting where the heater hoses attach to the engine. They are called truck valves. The engine should have a bypass so it doesn't require any flow through the heater circuit.
is it possible a blockage in the suction line? i have a temp reading of 45* to 48* on one side of a 45 degree elbow and it rises to 77* on the other side of the elbow im taking the readings 3 to 4 inches apart ?
Haven't work on these things for years, installations I have seen were add on and pretty sloppy with AC lines running along side that super hot exhaust manifold and an evaporator box mounted in the cab. Not sure what kind of system you have, did it ever work well before? Would help if you would post some photos.
the vent temp is now 40* i removed the heater lines and connected them together, she is cold, only hiccup is the fan switch,, it was working on all 3 positions yesterday but today after working for abit it stopped working on the high position , only off, low and medium are working and the vent temp reading (40*) is on the med setting, i tried to ck the fuse but wouldn't the fan switch not work at all if a fuse is blown? fyi todays ambient was 78 to 80 and much less humid
But was it working well before?
Typically what happens is the blower motor bushings runs dry on oil and the armature shaft rusts causing a drag on startup that blows your resistors. High is direct, that can blow your blower switch. If you want it to last, should also replace the blower motor as well. Use to be able to repair these motors, but that is becoming history. Like trying to reuse a beer can after it has been opened.
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