Kanaljen is offline
Join Date: Apr 2009
Rep Power: 14
Just sharing what I found over at the Viperclub forums...
Damn, I do a lot myself but this might be a job for a shop if the easy stuff are ruled out..
From Dave - 2BADD -4U:
First off....... to properly diagnose the systems operation ( efficiency ) a manifold gauge set should be connected to BOTH high and LOW sides of your ac system. Or as some call it the discharge and suction sides. This will immediately tell how the compressor is pumping, as your problem can be related to leaky valves of worn internal parts, identical to a cars engine...compression, etc. A normal operating system on a hot day with R-134a refrigerant would be "approx". 200#-275# high side and 30#-40# pressure low side. With a clear sight glass of course. Any bubbles indicate a low charge. To service the system properly for leaks; involves pressurizing the system with ref. or nitrogen, with a trace of r-134a and leak checking the complete system carefully. Gen 2 vipers had a prone leak on the schraeder valve stem fitting on the low side. Under the black plastic seal cap. The suction side or low side is always the larger line on the compressor and system, and the high or discharge lines are smaller and get extremely hot. The gauge fitting is a much smaller thread also, Guys years ago were hooking up small walmart ref. 12 cans to the high side and essentially had a hand grenade in their hands,as the higher discharge pressures would fill the can and tear it to pieces. NOT PRETTY!
The expansion valve rarely fails, but it can... most likely it gets restricted with debris, or moisture, causing freezing, as the oriface is the smallest passage thru out the whole system.
Note: with both gauges installed and while monitoring both pressures, have someone shut the ac off. Carefully watch the reaction of the presures, now ..IF you get an "immediate" equalization of the pressures, most likely the compressor is the culprit, and valves are worn badly, the compresor will not pump efficiently. With LOWER high side and HIGHER low side pressures. NOTE: That is NOT a way to check the expansion valve operation, as mentioned prior. With a working expansion valve, and good compressor efficiency, your low side pressures will always be 40# and much less. Also Lower with an increase in engine rpm.
Remember that refrigerant pressures and temperatures are ALWAYS linear all the time. Meaning Equal rises and drops in sequence to each other. A rise in pressures gives a rise in temps. and vice versa. Also be sure to check the low pressure safety cutoff switch, as they do fail, and can give a compressor short cycling operation. If you notice that the suction pressure goes up and down every few seconds, sometimes longer...you are either low on refrigerant, have a faulty/erratic low pressure switch, or a restriction in the system internally at the expansion valve.
It is difficult to hear the compressor short cycling because of the loud exhaust on all vipers, vs. normal quite cars, say like my Chevy Tahoe.
It is possible to have internal restrictions else where in the system but highly unlikely as the tubing has larger diameters. Bad condensors were mentioned above, but usually referred to LEAKS. Depending on the leak location, repairs can be attempted. And always a removal from the car is needed.
Always change the drier if the system has been prone to a history of leaks and ref. charges. As far as the expansion valve operation, you can tell by the system pressures. Also if your compressor is in-efficient your high side pressures will be lower than normal and your low , suction side will be higher than normal...example 125# and 80#...+ or -.
Usually if you see oil anywhere on the ac system or lines, it is a sure indicator of a ref. leak.
also under the hood rear the passenger side firewall on your gts, check the heater hose butterfly valve mechanism. its should be fully closed, or it may possibly let the hot antifreeze mixture flow thru the heater coil, eventually lowering your cooling effect. work the hot/cool dash control knobs and simulate hot/cool, and you can easily verify the flow or non flow of antifreeze.
also your ac system works its most efficient is during highway cruises...65-75mph not during idling. to check for a full charge have someone rev the motor to approx 1500-2000 rpms and check the site glass.
your ac system when operating properly, will have the suction lines being ice cold and sweating, dripping a lot of water drops. also check your condenser coil for any obstructions, example plastic wal mart bags, leaves, etc road debris. visibly check the condenser coil for blockage with bugs, insects, etc. if blocked, GENTLY rinse with a hose note GENTLY ...condenser coils rarely have problems with refrigerant flow,as the tubing is of good size. Unless your compressor lets loose and internally sends debris into the system, the coil rarely gets internally blocked, same with evaporator coil. External blockage is more prone to be causing a problem, as it will increase your high side pressure dramatically, also increasing your low/suction pressures which will in effect give less cooling effect. if you notice ice anywhere during system operation, there is a restriction or lack of refrigerant.
Try to stay away from the QUICK fixes like adding sealant or leak stoppers, as your systems oil, and lines become coated, especially the evaporator cooling coil, reducing thermal heat transfer....almost like using a can of fix a flat for tires.
also, place a pocket type pencil thermometer in the air vents, to check discharge air temp. will vary with o.a. temps, but generally will be between 48-60 degrees.from the vents, fan on high, increase engine rpms, and make sure that all condenser/radiator fans are all working properly!
the best way to confidently and accurately know the proper ref. charge is to evacuate the system and then weigh in the nameplate ref 134a charge with an accurate ref. weighing scale.
Hope this helps!