1998 Blazer-A/C Problem

[jmr1777]

I have a 1998 Blazer 4.3, the A/C once it does come on the compressor runs until it I turn it off. It doesn't cycle on and off like it should. The temp. reading that I am getting is around 59 degrees from the vents. I attempted to add R134a with a gauge and it was reading full already......The clutch once it starts doesn't diengage at all. Thanks for any advice on this matter.

Nashville, TN

[MT-2500]

If the AC system is low on r-134a it can do that.
But to safely add or check a ac system you need a ac recharge gauge set with a low and high gauge.
And a word of caution only use straight R-134a to add to a system.
Do not use anything like a wal mart death kit with the stop leak or dye or oil in the can.
We need your low and high side readings at idle and at 2000 rpm.
If your high side is reading over 250-300 lbs you have to much pressure.
On the compressor running all of the time check low side pressure with ac running and post back.
If it drops under 28 lbs the low pressure switch should turn off compressor.

[old_master]

The clutch cycling switch, located near the inlet of the accumulator, has an operating range of 22psi to 42psi. This range is designed to keep an average pressure of 32psi in the evaporator when the A/C is operating. When R134a is at 32psi, it is approximately 32 degrees Fahrenheit, (the temperature at which water freezes). If the average evaporator pressure drops below 32psi, condensation on the outside of the evaporator will freeze and block the airflow through it. The clutch cycling switch will allow the clutch to engage only when the pressure at the switch is above 42psi. When the compressor runs, evaporator pressure drops. When it reaches 22psi the cycling switch shuts off the clutch and the compressor stops. When the compressor stops running, the refrigerant pressure equalizes in the system between the high side and the low side. When pressure at the cycling switch rises to 42psi it turns on the clutch, the compressor runs and the cycle starts over again.

With any clutch cycling system, like yours is, it is impossible to tell how much refrigerant is in the system without first evacuating the system and measuring the refrigerant as it is being installed. As MT said, two gauges are necessary so that both high side and low side pressures can be monitored simultaneously while servicing and diagnosing the system. Stay away from the DIY charge kits, they can seriously injure or kill you.

Temperature readings taken at the registers are influenced by many things: System overcharged, system undercharged, poor compressor performance, too much oil in the system, ambient temperature, ambient humidity, clogged, torn or missing fixed orifice tube, restricted refrigerant line, and last but certainly not least, engine cooling system condition. The 59 degree reading you have, by itself means nothing without taking into consideration everything that influences the systems performance.

If you’re planning on diagnosing and repairing it yourself, a manifold gauge set and an evacuator are the bare minimum tools required to get started. Most auto parts stores have the gauge and hose sets available for somewhere around $125.00 Adequate evacuators start around $175.00 for the average DIYers occasional use. When you’re ready to properly, accurately and safely diagnose and repair the problem, we can help you.