# AC/Heater fan won't work on High **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** astro, heating, airconditioning\ **Created:** [July 10, 2007, 9:05pm UTC](https://community.cartalk.com/t/ac-heater-fan-wont-work-on-high/1547 "2007-07-10T21:05:55Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![wanpi17](https://avatars.discourse-cdn.com/v4/letter/w/eb8c5e/32.png) [@wanpi17](https://community.cartalk.com/u/wanpi17)\ **Post date:** [July 10, 2007, 9:05pm UTC](https://community.cartalk.com/t/ac-heater-fan-wont-work-on-high/1547/1 "2007-07-10T21:05:55Z")
My 91 Chevy Astro doesn’t like to blow air on high. The AC/Heater fan works fine at lower settings but when in high it doesn’t work at all or will run for 30 seconds and then stop. I’ve replaced the switch in the dash, but that didn’t help. Any ideas? ---
**Author:** ![system](https://global.discourse-cdn.com/cartalk/original/3X/1/d/1d47c66a543aa6c5a7873bb2320858f978ff52ed.png) [@system](https://community.cartalk.com/u/system)\ **Post date:** [July 10, 2007, 9:45pm UTC](https://community.cartalk.com/t/ac-heater-fan-wont-work-on-high/1547/2 "2007-07-10T21:45:26Z")
You need a new resister block. It’ll be located on/in the ductwork by the blower motor. A Haynes repair manual will show you where it is. - mountainbike ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [July 10, 2007, 10:09pm UTC](https://community.cartalk.com/t/ac-heater-fan-wont-work-on-high/1547/3 "2007-07-10T22:09:18Z")
[b]It isn’t the resistor block. The voltage for the fan high speed by-passes the resistor block. This sounds more like a problem with high speed fan relay. On the low speeds, the fan relay routes the voltage thru the resistor block. When you switch to high fan speed, the relay switches over to supply full voltage from the battery to the fan motor. Tester[/b] ---
**Author:** ![system](https://global.discourse-cdn.com/cartalk/original/3X/1/d/1d47c66a543aa6c5a7873bb2320858f978ff52ed.png) [@system](https://community.cartalk.com/u/system)\ **Post date:** [July 10, 2007, 10:30pm UTC](https://community.cartalk.com/t/ac-heater-fan-wont-work-on-high/1547/4 "2007-07-10T22:30:41Z")
Tester is right. I didn’t think through the question carefully enough. My mea culpa. Now if you’ll all excuse me while I go retract my foot from my mouth… - mountainbike ---
**Author:** ![system](https://global.discourse-cdn.com/cartalk/original/3X/1/d/1d47c66a543aa6c5a7873bb2320858f978ff52ed.png) [@system](https://community.cartalk.com/u/system)\ **Post date:** [July 10, 2007, 11:46pm UTC](https://community.cartalk.com/t/ac-heater-fan-wont-work-on-high/1547/5 "2007-07-10T23:46:46Z")
Star… you manage to come up with the wrong answer again. Relays are not used to switch fan speeds, a resistor block is. Plus there are NO electronic commuted motors in a automotive application. ---
**Author:** ![willey](https://avatars.discourse-cdn.com/v4/letter/w/a9adbd/32.png) [@willey](https://community.cartalk.com/u/willey)\ **Post date:** [July 10, 2007, 11:49pm UTC](https://community.cartalk.com/t/ac-heater-fan-wont-work-on-high/1547/6 "2007-07-10T23:49:20Z")
This vehicle uses a resistor block to switch fan speeds. No relays involved in the lower speed circuit. ---
**Author:** ![system](https://global.discourse-cdn.com/cartalk/original/3X/1/d/1d47c66a543aa6c5a7873bb2320858f978ff52ed.png) [@system](https://community.cartalk.com/u/system)\ **Post date:** [July 11, 2007, 1:45am UTC](https://community.cartalk.com/t/ac-heater-fan-wont-work-on-high/1547/7 "2007-07-11T01:45:10Z")
I can only guess after reading the other posts that a wire break or loose or corroded connector may be causing the problem. Dropping resistors, inside the fan plenum, can sometimes get wet and then corrode. It’s worth a look. A relay should not be needed for switching to high speed. This can be handled with the selector switch and would be less expensive and less complicated for the mfr. ---
**Author:** ![EllyEllis](https://avatars.discourse-cdn.com/v4/letter/e/f14d63/32.png) [@EllyEllis](https://community.cartalk.com/u/EllyEllis)\ **Post date:** [December 18, 2008, 5:37am UTC](https://community.cartalk.com/t/ac-heater-fan-wont-work-on-high/1547/8 "2008-12-18T05:37:06Z")
Tester is 100% correct. ---
**Author:** ![klt](https://avatars.discourse-cdn.com/v4/letter/k/bcef8e/32.png) [@klt](https://community.cartalk.com/u/klt)\ **Post date:** [December 27, 2008, 8:46pm UTC](https://community.cartalk.com/t/ac-heater-fan-wont-work-on-high/1547/9 "2008-12-27T20:46:48Z")
I had this problem last year. The high speed relay is on the resistor block. It is located undr the hood on the left side of the firewall facing the vehicle. The replacements are not a perfect fit and you will have to file a bit on the plastic opening before the new resistor block will fit. Hard to see and will have to estimate by feel.