Heater Hi not working - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mikep · 09-25-2002, 12:30 AM

I put my heater on hi but no worky. Just makes a growling sound. Its got a new heater relay. Doesnt seem like a switch problem. Is there a resistor or something I am missing here. It only does this in the hi range. This is an air conditioned truck if that makes any difference

mtdave2 · 09-25-2002, 12:50 AM

sounds more like the fan motor to me. run a wire from the battery to the fans power terminal (in the engine compartment) see if the fan runs on high that way. if it doesnt, bad fan, if it does, prob one of the other things.

there are 3 major causes for this. first is the switch. 2nd is that relay (right of the glove box under dash) and the third... um, name is escaping me right now, but its INSIDE the duct work just below and to the left of the glove box. only thing left is the fan motor.

good luck, i chased mine for a month before i found out it was mis wired at the switch!

barn9 · 09-25-2002, 01:19 AM

I once had a bad wire going to the high speed relay under the glove box. The wire was half melted from getting too hot. When I re-built the harness, it got a little heavier wire.

mrein3 · 09-25-2002, 07:27 AM

A lot of GM cars and trucks have an in-line fuse for the high-speed position on the fan. Look for an orange wire along the top of the firewall.

Huck · 09-25-2002, 07:47 AM

Had same problem with two different a/c trucks. In both cases it turned out to be bad grounds---one at the relay and one at the motor it's self. High speed fan failure seems to be a common problem with the wiring design on these trucks~~~.

Hutch · 09-25-2002, 09:50 AM

Try the Ground wire from the high speed relay behind the glove box. There is a short wire from relay base to the firewall mountingbolt that is nearby.
It could also be the ground inside the engine comparment from firewall to the fan base.

Symption are low speed is very slow, Medium speed works and High returns to a very slow speed

You can use a small section of wire for a test.

The plastic plug to the fan switch under the dash carries alot of current and is usually melted, make sure it is making a good connection.

Have fun

09-25-2002, 12:30 AM	#1
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	Heater Hi not working I put my heater on hi but no worky. Just makes a growling sound. Its got a new heater relay. Doesnt seem like a switch problem. Is there a resistor or something I am missing here. It only does this in the hi range. This is an air conditioned truck if that makes any difference __________________ No truck :-(

09-25-2002, 12:50 AM	#2
mtdave2 newly minted old timer Join Date: Dec 1999 Location: Hudson WI Posts: 3,521	sounds more like the fan motor to me. run a wire from the battery to the fans power terminal (in the engine compartment) see if the fan runs on high that way. if it doesnt, bad fan, if it does, prob one of the other things. there are 3 major causes for this. first is the switch. 2nd is that relay (right of the glove box under dash) and the third... um, name is escaping me right now, but its INSIDE the duct work just below and to the left of the glove box. only thing left is the fan motor. good luck, i chased mine for a month before i found out it was mis wired at the switch! __________________ ____________________________________________ 72 c20 longhorn 65k org miles and counting! 69 k10 Suburban

09-25-2002, 01:19 AM	#3
barn9 Half a bubble off! Join Date: Jun 2000 Location: Winfield, Ks, USA Posts: 5,588	I once had a bad wire going to the high speed relay under the glove box. The wire was half melted from getting too hot. When I re-built the harness, it got a little heavier wire. __________________ Just call me LB. '71 Cheyenne, 402BB, hauls blondes, brunettes, or redheads.

09-25-2002, 07:27 AM	#4
mrein3 Registered User Join Date: Feb 2000 Location: Center City, MN, USA Posts: 3,254	A lot of GM cars and trucks have an in-line fuse for the high-speed position on the fan. Look for an orange wire along the top of the firewall. __________________ '70 cab, '71 chassis, 383, TH350, NP205. '71 Malibu convertible '72 Malibu hard top Center City, MN

09-25-2002, 09:50 AM	#6
Hutch Registered User Join Date: Oct 2001 Location: Grapevine, Tx. Posts: 2,142	Try the Ground wire from the high speed relay behind the glove box. There is a short wire from relay base to the firewall mountingbolt that is nearby. It could also be the ground inside the engine comparment from firewall to the fan base. Symption are low speed is very slow, Medium speed works and High returns to a very slow speed You can use a small section of wire for a test. The plastic plug to the fan switch under the dash carries alot of current and is usually melted, make sure it is making a good connection. Have fun __________________ John Hutchison Grapevine,Texas 68 1/2 t swb 68 Mustang 69 Jaguar 71 1/2 t swb 88 Supra CompTs6m 93 Escort GT 2005 Corolla XRS

09-25-2002, 07:47 AM	#5
Huck Senior Member Join Date: Jun 2001 Location: Shelbyville, KY Posts: 3,261	Had same problem with two different a/c trucks. In both cases it turned out to be bad grounds---one at the relay and one at the motor it's self. High speed fan failure seems to be a common problem with the wiring design on these trucks~~~.



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