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frightliner fl80 ac issue Pages: 12

ctkiteboarding on Wed June 01, 2011 9:30 PM User is offline

Year: 1998
Make: freightliner
Model: fl80
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

ctkiteboarding on Wed June 01, 2011 10:08 PM User is offline

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*

mk378 on Wed June 01, 2011 10:09 PM User is offline

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?

mk378 on Wed June 01, 2011 10:11 PM User is offline

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

ctkiteboarding on Wed June 01, 2011 10:29 PM User is offline

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

ctkiteboarding on Wed June 01, 2011 10:31 PM User is offline

the heater water line valve seems cheap and kind of sloppy , also hard to switch from the cab

mk378 on Wed June 01, 2011 10:32 PM User is offline

With the heater shut down, heater hoses should not be warm or hot. The vent temperature should be close to the suction line temperature.

ctkiteboarding on Wed June 01, 2011 10:32 PM User is offline

would it hurt to pinch this line closed temporarily
to see if vent temps lower?

ctkiteboarding on Wed June 01, 2011 10:33 PM User is offline

suction line temp?? sorry new to this ,, where is this and how can i get a temp reading to compare?

mk378 on Wed June 01, 2011 10:36 PM User is offline

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.

ctkiteboarding on Wed June 01, 2011 10:38 PM User is offline

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*?

mk378 on Wed June 01, 2011 10:49 PM User is offline

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.

ctkiteboarding on Wed June 01, 2011 10:57 PM User is offline

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

mk378 on Wed June 01, 2011 11:01 PM User is offline

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.

ctkiteboarding on Wed June 01, 2011 11:04 PM User is offline

do u think ill overheat the engine by closing these two lines into the cab? this should not effect coolant flow
correct?

ctkiteboarding on Wed June 01, 2011 11:05 PM User is offline

ill look for shut offs and try a tempory clamp

mk378 on Wed June 01, 2011 11:27 PM User is offline

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.

ctkiteboarding on Wed June 01, 2011 11:29 PM User is offline

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 ?

NickD on Thu June 02, 2011 7:22 AM User is offline

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.

ctkiteboarding on Thu June 02, 2011 4:32 PM User is offline

bingo!!!
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

ctkiteboarding on Thu June 02, 2011 4:36 PM User is offline

Quote
Originally posted by: mk378
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.

could not find the hand valves you speak of i agree most ive seen have them, my thoughts are to install a simple ball valve on each line

ctkiteboarding on Thu June 02, 2011 5:47 PM User is offline

Quote
Originally posted by: NickD
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 truck has a behr system serial # 013098-1 and a behr # 8520030100 not sure if its aftermarket or oem


NickD on Fri June 03, 2011 6:34 AM User is offline

But was it working well before?

ctkiteboarding on Mon June 06, 2011 10:30 PM User is offline

Quote
Originally posted by: NickD
But was it working well before?


never had to use it , truck was purchased in the fall, the damn thing was alway hot as hell in the cab,

ive replaced the heat temp valve and put a new switch in , the resistor comes tues for the switch so im hoping that will get the fan to blow onthe high setting, the fan was working on high, it quit just the other day, its cold now with the heat lines bypassed,
id like a remote ball valve to be able to switch it from the cab, ,, the stock heat temp valve is after the core so it will still have the reheat issue i feel


NickD on Tue June 07, 2011 7:21 AM User is offline

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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