A/C button not engaging to relay. help?

[Jacob01]

Howdy yall,

Looking for some help here. So of course A/C quits working. I have started with a few simple tests
1. Fan control and cold/hot air work
2. A/C button lights up and fuse is good
3. pulled relay under hood, I have the main power from battery, and power when I turn on key
when I start up truck and turn on the A/C button it does not light up tester, assuming my problem is from
A/C button to fuse box under hood, any suggestions on how to move forward?
additional info.. I used a light tester to check fuse connection for relay, of the four holes that the relay sits in the top two are lighting up side by side, when key is on. I am not getting anything to light up tester on bottom two holes when I turn on the A/C button on dash. any suggestions would be great... thanks

 

[Jacob01]

Will I need to take dash apart to diagnose wire or is there another connection somewhere to check first?

 

[MassHoe04]

I am not the HVAC expert, but someone will ask, so it might as well be me...
Is it Auto (electronic temp settings, etc.) or manual controls with knobs?

Too early to tell yet, but the issues a lot of people have on the forum is often related a bad controller. Those tend to be fairly cheap and easy replacements. That's the module in the dash with the HVAC control buttons. Let's hope it ends up being an easy fix like the controller module.

The more information you can give along the way, the better chance someone can help you.

 

[Jacob01]

I am not the HVAC expert, but someone will ask, so it might as well be me...
Is it Auto (electronic temp settings, etc.) or manual controls with knobs?

Too early to tell yet, but the issues a lot of people have on the forum is often related a bad controller. Those tend to be fairly cheap and easy replacements. That's the module in the dash with the HVAC control buttons. Let's hope it ends up being an easy fix like the controller module.

The more information you can give along the way, the better chance someone can help you.

Thank you for your reply. It is manual knobs for temp control and fan. Plus a push button for A/C. So you are saying it might be the button I push for A/C on or off? Probably a good place to start.

 

[MassHoe04]

Not suggesting the on/off button, specifically... Possibly something on the circuit board inside that control module.

Just putting it out there, that HVAC control modules can make the systems do weird things or not work at all.

I am sure there will be additional steps and tests people will have you work through before having you run out to buy a control module, but that might be a possibility depending on what you find out.

 

[exp500]

Look at bottom of relay, give pin numbers of where power is again. See that A/C control is in on positon. test again in off.
Try swapping in a different relay.

 

[jwth]

it would help to know what year

 

[jwth]

there is an ambient outside air temperature sensor that fails quite often. Located behind the right hand headlight assembly
little bulb thingy attached to the plastic inner cowl

 

[Jacob01]

Thanks guys for your replies. I did go to junk yard and replace the control module with a used one. I didn’t realize that was all one piece. Anyways that did not fix it. This is a 2001 Yukon XL. I will look for ambient outside air sensor and check it. As for the relay, on top is 85 and 87. Bottom is 86 and 30. 85 is power from battery. 87 is power from key switch. Now 30 should be power from A/c on/off button. But no power, nor power to 86 for that matter if I have them backwards.