Join Date: Apr 1999
Location: Justin,Texas, Republic of TEXAS (USA)
Feedback Score: 0 reviews
these trucks have CCOT refrigerant system and pressures tell you little about low charge.
If you take an appropriate sized stick, pipe, a level, etc that can be inserted between seat and accel pedal and slide seat forward so that throttle is applied to get engine to 1300-1500 rpm. Set fan to one speed below high and use a thermometer (meat thermometer, etc that will read 30-100 degrees) inserted into center vent. Set control to MAX, if auto temp control set it to coldest temp and manually set fan speed as above.
A good gauge of charge level is to allow it to run in the conditions above and see if the large diameter line that runs down to compressor is as cold or nearly as cold as the large diameter line from evaporator case into the accumulator (aluminum canister in front of passenger side firewall case). If nothing is cold it is low or other problems exist. If the evap line is cold and the compressor is not then it is likely low and you can add R134a as a gas (can top up) for a minute and then shut off can valve. see if the compressor line is cold. If not repeat the gas adding phase and then monitor phase until the compressor line is cold. Better to go slow and monitor than to add liquid (can top down) and have it get overcharged or damage compressor from oil wash-out.
amb temp 80 L- ranges between 23-45 as compressor cycles
amb temp 90 L- lower 30's but should also range 23-45 after it cools down inside truck H 200-240
If the high side pressure is higher than the values listed you could have bad airflow from debris in condenser-rad-intercooler or fan clutch is not working properly or it has an obstruction in orifice.
Low side going rapidly to 23 psi and then the pressure on low side cycles rapidly between 23-45 with rapid compressor on-off can be low charge.
Low side being higher than what is listed above and high side being lower is usually faulty compressor having poor pumping-compressing capability.
Vent temp in the conditions as above after several minutes of running with windows up, doors closed should yield vent temps of 50F or a little below.
Debris on evaporator can cause everything to be OK pressure wise with vent temps not low enough. Heater door not fully closing can cause this too. Crimping heater hose shut and watching temps several minutes will tell you if it is heater door issue.
Don't tell my cattle I got leather seats!
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Last edited by jimmy; 06-13-2010 at 06:47 PM.