A/C Question

[drwombat]

Hey guys I'm having A/C woes (excuse my terminology). I replaced the resistor for my blower motor about 9-12 months ago per recommendation of the specialist (what an honest guy).

His right hand man recharged my frion for me less than a week later also around a year ago, now I'm having problems when I turn the ac knob to 4 or 5 and it blows hot air. Not always but sometimes.

It has only done this to me a handful of times and I've noticed (but havent tested) that when I turn the truck off then back on it "could" be solving the hot air problem. (not really a fix though)

My dad reccomended leaving the a/c on low because he thought the compressor was going bad, on a long road trip I did notice the A/C Leaking from under the dash if this helps any pro's with a diagnosis

Last time it blew hot air was maybe a month ago and I havent actually been cranking the a/c up but have had it blowing steady every time I drive (usually b/w speeds 1-3)

It is the middle of summer in Texas so you might empathize with my concerns

[KirkW]

What year Suburban are we discussing here?

Earlier vehicles only ran the A/C compressor when the vent selector was in the "A/C" or "Defrost" position. Later trucks have a separate "A/C" button that allows you to turn on the A/C compressor in any vent position (useful for those cool, wet rainy days when you want dehumidified heat at your feet).

With most GM systems of the past two decades or so, when the A/C compressor is enabled it is running "full blast", making as much cold as possible. The temperature is controlled only by adding more or less hot air from the heater core.

The blower motor doesn't have any direct affect on the temperature - it simply blows more or less air through the system. However, if your A/C is low on refrigerant (aka - 'Freon', or the newer R-134a), then the air isn't cooled enough. At low blower speeds it may feel cool, but at high speeds the air doesn't linger long enough to be cooled down by the evaporator, so it feels warm.

But now some direct questions - what do you mean by "A/C Leaking from under the dash"? Do you mean water is dripping from under the dashboard? If the A/C system was leaking you'd never see it directly - the refrigerant is an invisible gas. At most, all you'd see is a bit of compressor oil around the site of the leak. So most likely what you see 'leaking' is really water. This water is condensed from the humid outside air (that's why it's called 'condensate').

It's quite normal for this water to leak outside the truck. There is a drain in the A/C system to allow this condensate to drain overboard. If it's leaking inside the truck then it means the drain is clogged. This usually results in a water-soaked carpet and a musty odor, but the A/C should still work.

I suspect your real problem is the system is low on refrigerant. Try this simple test - start the truck and turn the A/C on full blast - max blower speed, max cold temperature with the windows up and the doors closed. Open the hood and observe the A/C compressor. The entire pulley should be spinning. Occasionally the face of the pulley will stop spinning as the A/C clutch disengages. This on/off cycle repeats as the compressor keeps things cool. This cycling should not be rapid. On a hot day (80+ degrees F), the compressor should be running almost constantly. If instead it is turning on and off every couple of seconds then it's very low on refrigerant.

So let's say you've passed the first test. Next, find the two aluminum A/C lines that go to the evaporator. These two pipes are about an inch thick and go through the firewall. One line goes from the firewall to a big aluminum can called the Receiver/Dryer. The other line should come out of the firewall less than a foot away (sometimes only a few inches). Feel these two lines - both should feel cold when the system is running. If the line without the Receiver/Dryer feels cold, but the line with the Receiver/Dryer feels warm, then you're too low on refrigerant.

If you have to keep adding refrigerant, then it means there's a leak. Ideally, get the leak repaired. Simply adding refrigerant is a stop-gap measure at best. Also, if not done properly adding refrigerant (especially with the DIY kits) can also push outside air into the system. This air prevents a full charge of refrigerant from getting in. This means the system will never get as cold as it should even though it's "fully charged".

Report back with your findings - we'll get you chilly again!