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95 S_Trucker · 06-28-2018, 02:56 PM

You are correct the the resistor only affects speeds 1-3. High is controlled by the relay. Most likely the relay is the problem. If you lower the glovebox, you should be able to see the relay hiding up there. It sounds like you already found it.

There is a small chance(less than 5%) that the problem is in the switch. I've replaced a decent amount of relays in these trucks.

In the future, you will probably get a better response in the 88-98(gmt400) section.

06-28-2018, 02:56 PM	#2
95 S_Trucker Registered User Join Date: Oct 2009 Location: . Posts: 2,179	Re: 99 K1500 Suburban no high speed ac fan You are correct the the resistor only affects speeds 1-3. High is controlled by the relay. Most likely the relay is the problem. If you lower the glovebox, you should be able to see the relay hiding up there. It sounds like you already found it. There is a small chance(less than 5%) that the problem is in the switch. I've replaced a decent amount of relays in these trucks. In the future, you will probably get a better response in the 88-98(gmt400) section.