2005 GMC 1500 Air Conditioning AC Not Working

onecrazyfoo4u · March 22, 2016

I bought the truck over winter and failed to check it out for proper AC working. I had a feeling something was up when I could never feel the compressor kick on during defrost usage over winter. Now that it's warmer, I can definitely tell the compressor isn't turning on...just blows warm air. The light turns on via the HVAC control panel, but nothing happens.

Where should I start? I have some R134a refill kit with a gauge. Should I try topping off the system? What psi should it be at?

If topping it off doesn't work, where should I check next? Thanks for any help!

Daryl Z71 · March 22, 2016

Before buying anything for the system, take a look under the hood down at the compressor itself. Make sure that the belt and Pully system for it is still in tact.

onecrazyfoo4u · March 22, 2016

Before buying anything for the system, take a look under the hood down at the compressor itself. Make sure that the belt and Pully system for it is still in tact.

Will do for sure. I'll make sure it's spinning properly and try to check for any leaks. How do the fans work? Should they turn on instantly when I enable AC?

Daryl Z71 · March 22, 2016

Will do for sure. I'll make sure it's spinning properly and try to check for any leaks. How do the fans work? Should they turn on instantly when I enable AC?

Mine turn on pretty quick, but it's usually just the one.

hiking_mike · March 23, 2016

Also, before doing anything. use a paperclip and short out the low pressure switch. if the compressor kicks on, this is good.

If not, there are other problems with the compressor. if the high pressure switch is good then A/C should kick on, if not, try disconnecting the high pressure switch. It works in the exact opposite manner of the low side.

On an 06, the low side switch is on the side of the accumulator-drier. Disconnect and use a paper clip to short the leads. The low side switch is normally open and will close if there is enough refrigerant pressure.

the high side is normally closed and opens with there is too much pressure.

00Silverado4x4 · March 23, 2016

Also, before doing anything. use a paperclip and short out the low pressure switch. if the compressor kicks on, this is good.

If not, there are other problems with the compressor. if the high pressure switch is good then A/C should kick on, if not, try disconnecting the high pressure switch. It works in the exact opposite manner of the low side.

On an 06, the low side switch is on the side of the accumulator-drier. Disconnect and use a paper clip to short the leads. The low side switch is normally open and will close if there is enough refrigerant pressure.

the high side is normally closed and opens with there is too much pressure.

^^^ This first before anything else.

onecrazyfoo4u · March 23, 2016

Also, before doing anything. use a paperclip and short out the low pressure switch. if the compressor kicks on, this is good.

If not, there are other problems with the compressor. if the high pressure switch is good then A/C should kick on, if not, try disconnecting the high pressure switch. It works in the exact opposite manner of the low side.

On an 06, the low side switch is on the side of the accumulator-drier. Disconnect and use a paper clip to short the leads. The low side switch is normally open and will close if there is enough refrigerant pressure.

the high side is normally closed and opens with there is too much pressure.

Is there a diagram or picture somewhere that shows where this stuff is? I've never really done troubleshooting on an AC system before. Thanks!

hiking_mike · March 23, 2016

Disconnect this connector. Short the 2 pins inside the connector with a paper clip. make sure the A/C is turned on and the engine running.

as soon as you insert the paper clip, the compressor clutch should engage. The clutch is a electromagnetic clutch that will energize. then the compressor pump should start turning along with the belt.

If it does not, use a volt meter to see if 12 volts is being sent to the clutch. If 12 volts is present at the clutch and the compressor is still not engaging ( you should hear a click the clutch will engage ) Then either the compressor is bad or just the clutch.

Don't ask why, but the cost of a clutch is about 80% or more the cost of an entire compressor with clutch.

Now, if you short out the low pressure switch and the compressor kicks on, then you may be low on Freon.

Connect a pressure gauge to the low side port, don't worry, on newer cars, the high and low side ports are different sizes.

Now for basic A/C pressure principles. You HVAC Professionals please forgive me if I mis quote pressures or exact principles)

You need so much pressure to activate the low side switch. Which by inserting the paperclip, you are telling the pump to start running regardless of pressure.

With the A/C compressor not running, think of the Freon as a gallon of milk. Sort of like 2 quarts on the low side and 2 quarts on the high side.

As the pump starts to work, the low side will go lower and the high side will go higher. Then you will end up with 1 quart on the low side and 3 quarts on the high side. ( don't worry, unless you have a full set of pressure gauges, you cant read high side with the normal over the counter A/C re charge kit.

You will see the pressure gauge swing wildly as the pump cycles. and you start to add Freon.

on a normal temp day, like in the mid 70's to mid 80's you should have about I think 32 to low 40's pounds of pressure. At static I think you should be around the mid 70"s on the low side.

As a guide, look on the fender, you will see a sticker of the refrigerant type and amount, if you are completely empty.

Most leaks are around connections, and the pump itself.

I have seen quite a few leaks at the A/C port itself. This is like a bicycle valve core called a Schrader valve.

IF the Freon is completely out, you may have an issue of a leak that should be fixed.

Then a complete vacuum of the system should be preformed to ensure all moisture, etc is out of the system.

But you can simply add Freon or , refrigerant and get you up and running.

I believe ther is a product that is almost like a can of "Add me first" if you are completely empty. I have never used this but I believe it is supposed to help with moisture issues.

Again, you get what you paid for, do it your self and you will save money. remember that if you install a new compressor, normally most parts stores will not warranty the compressor unless you follow recommended steps and/or purchase additional items like a new drier, etc...

A/C systems are not that complicated.

Now on the other hand those darn actuators under the dash can be a pain to get to. I think there are 4 of these. Most parts stores sell them. be careful, some are interchangeable and others are not.

There is a HVAC reset procedure which can be found onthe internet. I think it is remove the fuses and turn key on for so long, turn off and wait for so long.

If you have the Electronic controls, there are known issues with the blower resistor.

lastly there is a HVAC self diag mode, sort of like how Dodge cars can give you the service engine codes by turning the ignition key off and on 3 times. Heck, there is also a Dodge instrument cluster self diag mode also.

BUT, I have never been successful in entering into the HVAC self diag mode.

silveradosid · March 26, 2016

put a pressure gauge on first to see if there is any Freon in the system. if it is anything below 15 psi you have a leak. do you access to a vacuum pump

Nanotech Environmental · March 28, 2016

In addition to what is posted above, these compressors won't operate if the oil level in the system is too low.

onecrazyfoo4u · April 5, 2016

Thank you so much hiking_mike. Awesome detailed explanation. I've been on vacation, but will get to checking this out soon.

Haven't needed AC, since winter doesn't seem to want to end around here. 30's one day with snow, then 60's the next day. Such random storms going on lately!

onecrazyfoo4u · April 12, 2016

So I did the paperclip trick and nothing happened, no AC clutch engagement. I checked the voltage at that connector, and it's only getting 4.7v on the one connector pin. But it's always 4.7v, whether the AC or truck are on or off. So what does that mean? No signal being sent from the hvac computer? When I push the AC button the little snowflake light turns on. The clutch belt was a little loosw, but in tact and spinning. Would it be a problem to have a little slack?

When I plug in the Freon gauge it shows 80 to 90 psi, in the red. Is that cause the clutch isn't engaging?

muddkatt · April 12, 2016

80-90 psi means it has a good charge, so that is not the problem. Belt should be tight, it has an tensioner pulley. Unplug the clutch connector and test the voltage going to the compressor with the truck running and the AC on. Should have 12-14 volts.

onecrazyfoo4u · April 12, 2016

Okay thanks, I'll check the voltage at the compressor clutch connection. If that checks out to 12v does that mean it's a bad compressor? Nothing else that could be wrong if it's getting voltage right?