GMC truck A/C not cooling in town

In my experiance the A/c looses efficiency whenever the airflow through the radiator (for lack of the right word) is reduced as in city driving.

In my vehicle the radiator fan switches on to boost airflow.

Does your truck have electric or mecahnical fans? If electric make sure they both are working and if mechanical make sure the fan clutch is in good shape.

Also if you can check the high and low side pressures while it is in "not cooling good" mode we can offer a little better advice.

Steve B.

Here are a few checks you can perform without getting out your gauge set.* My experience has been that a/c is something GM did well in this class of vehicle, and when functioning properly it should make things good and cold.

1. Under circumstances when you think it should be cooling but isn't, is the compressor clutch engaged? If you can't tell from behind the wheel, find a parking spot where you can safely leave the engine running and pop the hood and take a look. Some cars (dunno about this one) have demand cutoffs that temporarily disengage the a/c compressor when you accelerate, which you do a lot more often around town.

1. Does it give more satisfactory results on the MAX a/c setting? MAX closes the air-circulation intakes, so you are recirculating the cabin air and making it cooler and cooler rather than admitting hot outside air.

2. What does your engine temperature gauge look like when this is going on -- nominal, or getting pretty hot?

1. Is the temperature changer knob or slider all the way over to "Cool"... and is the heater core aware of that fact? Unless they changed it (along with several other things) between my '95 and your '96, make sure the cable linkage between the two hasn't gotten slack enough to be giving you heat...

Best of luck,

--Joe

• Though presumably you have a gauge set if you've been recharging your own a/c... most cars have an overpressure cutoff switch in the circuit, which presumably could be tripping under some circumstances if you put too much in.

One of the widely available consumer-grade brands of gauge, Interdynamics if memory serves, comes with a handy guide for interpreting the high-and low-side reading and needle behavior and other easily observed data.

The airflow issues others mentioned are very likely. Make sure the fan clutch gets stiffer as radiator temps increase. On a really hot day sitting still it should practically lock up, causing that roaring sound you are probably accustomed to. Other than that...

The blower speed switches are good for intermittant failure on your GM. When your problem occurs, look at the A/C button and make sure the light on it is lit. If the A/C button is depressed and the blower knob is set to anything but "Off", then you probably have a bad blower switch if the A/C indicator light is off.

It's actually more common for the blower switch to cause A/C compressor engagement when in the "Off" position, but any problem is possible with this GM switch.

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