AC/Heater blower motor does not work on high. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Bandit130 · 09-05-2019, 10:38 PM

Searched and did not find this issue. The blower motor shuts off when switched to high. Works on all other speeds. Not sure if it switch, relay, or the motor. Suddenly stopped yesterday while using AC. Changed to Bi-level to use the fan speeds, except high.

I did run a jumper from B+ to blower motor, and motor did run on high. Removed connectors from relay and resistor and reset both and no change. I will remove connectors and clean contacts tomorrow and I am planning to have the resistor tested by a co-worker that is an electronics engineer to see if it is still good. May need a new resistor or relay, not sure yet.

**MikeB** · 09-06-2019, 03:45 PM

The resistors are used to drop voltage for low and medium speeds. They are bypassed when the dash switch is set to HI speed. The problem is probably the dash switch itself or the connection to it. Neither would be an uncommon problem.

Bandit130 · 09-06-2019, 06:50 PM

Today removed relay, cleaned connector prongs, took apart and cleaned contacts. No difference. I was tapping on relay and fan came on high for maybe a minute then stopped. Decided to replace relay and still same problem. Also removed resistor, inspected and cleaned contacts and same problem.

Tomorrow, plan to remove climate control unit just enough to inspect unit and switch. I have inspected and lubricated temp lever when I bought truck cause lever was super hard to move. All things have been working well lately until this.

Bandit130 · 09-07-2019, 04:02 PM

Figured out the problem. There is an orange 10 ga wire on motor relay that goes thru harness to firewall that has an inline fuse connected to the junction block. The fuse holder was burnt. Replaced fuse holder, now have the high speed on blower. This wire has a constant 12v.

**Palf70Step** · 09-08-2019, 07:39 AM

Glad you found the issue. Never have seen a fuse holder on one.

09-05-2019, 10:38 PM	#1
Bandit130 Registered User Join Date: Dec 2014 Location: Euless, Texas Posts: 520	AC/Heater blower motor does not work on high. Searched and did not find this issue. The blower motor shuts off when switched to high. Works on all other speeds. Not sure if it switch, relay, or the motor. Suddenly stopped yesterday while using AC. Changed to Bi-level to use the fan speeds, except high. I did run a jumper from B+ to blower motor, and motor did run on high. Removed connectors from relay and resistor and reset both and no change. I will remove connectors and clean contacts tomorrow and I am planning to have the resistor tested by a co-worker that is an electronics engineer to see if it is still good. May need a new resistor or relay, not sure yet. __________________ 1974 Cheyenne 10 LWB Stock 350 W/HEI /TH350/AC/4 BBL Quadrajet Mopar by Birth Chevy by Choice

09-06-2019, 03:45 PM	#2
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,597	Re: AC/Heater blower motor does not work on high. The resistors are used to drop voltage for low and medium speeds. They are bypassed when the dash switch is set to HI speed. The problem is probably the dash switch itself or the connection to it. Neither would be an uncommon problem. __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

09-06-2019, 06:50 PM	#3
Bandit130 Registered User Join Date: Dec 2014 Location: Euless, Texas Posts: 520	Re: AC/Heater blower motor does not work on high. Today removed relay, cleaned connector prongs, took apart and cleaned contacts. No difference. I was tapping on relay and fan came on high for maybe a minute then stopped. Decided to replace relay and still same problem. Also removed resistor, inspected and cleaned contacts and same problem. Tomorrow, plan to remove climate control unit just enough to inspect unit and switch. I have inspected and lubricated temp lever when I bought truck cause lever was super hard to move. All things have been working well lately until this. __________________ 1974 Cheyenne 10 LWB Stock 350 W/HEI /TH350/AC/4 BBL Quadrajet Mopar by Birth Chevy by Choice

09-07-2019, 04:02 PM	#4
Bandit130 Registered User Join Date: Dec 2014 Location: Euless, Texas Posts: 520	Re: AC/Heater blower motor does not work on high. Figured out the problem. There is an orange 10 ga wire on motor relay that goes thru harness to firewall that has an inline fuse connected to the junction block. The fuse holder was burnt. Replaced fuse holder, now have the high speed on blower. This wire has a constant 12v. Attached Images __________________ 1974 Cheyenne 10 LWB Stock 350 W/HEI /TH350/AC/4 BBL Quadrajet Mopar by Birth Chevy by Choice

09-08-2019, 07:39 AM	#5
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 47,228	Re: AC/Heater blower motor does not work on high. Glad you found the issue. Never have seen a fuse holder on one. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!



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