Heater - A/C switch question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

danadena1960 · 02-25-2004, 02:02 AM

Hey All,
I have a 1977 K-20 with A/C. When I bought the truck the blower motor did not work on the HI setting or with the A/C setting on MAX. I replaced a resistor and relay on the heater box. Now everything seems to work fine, but I have noticed when I hit a bump it quits then comes back on. This happens only in the HI setting, all other setting do not seem to be bothered. I was telling this to a buddy and he said being I have the dash all apart I should change the actual switch on the insurment panel. He said those switches are common to go out and LMC sells them for $10. Has anybody else heard of this problem?
Thanks,
Dana

NeCrOmAnCeR · 02-25-2004, 02:36 AM

Be sure to check the relay. High speed bypasses the resistor block entirely. Look at the evaporator box in the engine compartment near the resistor block. You will find a metal relay. Be sure to check the connections to it and the inline fuse for it also. (all located near the evap). If the blower cuts out in the max A/C position also, this is the cause.

danadena1960 · 02-25-2004, 03:07 AM

Hello,
I did replace the relay, that is what in my opion got it fired up again. My El Camino use to eat them up all the time, why, I have no idea. Now it is a heater delete car. I did not know about the fuse though, I will look into that. How about the switch, have you ever heard of them going bad?
Thank you very much for the info.,
Dana

NeCrOmAnCeR · 02-25-2004, 11:50 AM

Yes, they do go bad. Just wanted to make sure that the easy things were checked first. If you wiggle the switch I'd expect the blower to work intermitantly since you stated that the blower will act up when hitting bumps. The inline fuse is between the relay and terminal block where the relay draws power. Mine is a 74 GMC, I think the 77's were similar. The spring in the fuse holder on mine had gotten hot and collapsed, which caused intermitant contact with the fuse. Good luck.

danadena1960 · 02-25-2004, 12:06 PM

Thank you very much, I will check it out.
Thanks again for the infor.
Dana

02-25-2004, 02:02 AM	#1
danadena1960 Registered User Join Date: Aug 2003 Location: Stockbridge, GA (Suburbs of Atlanta) Posts: 126	Heater - A/C switch question Hey All, I have a 1977 K-20 with A/C. When I bought the truck the blower motor did not work on the HI setting or with the A/C setting on MAX. I replaced a resistor and relay on the heater box. Now everything seems to work fine, but I have noticed when I hit a bump it quits then comes back on. This happens only in the HI setting, all other setting do not seem to be bothered. I was telling this to a buddy and he said being I have the dash all apart I should change the actual switch on the insurment panel. He said those switches are common to go out and LMC sells them for $10. Has anybody else heard of this problem? Thanks, Dana __________________ Dana 77 K-20 454 73 SS El Camino 454 68 SS Camaro 327 48 Chevy 216 755 John Deere

02-25-2004, 03:07 AM	#3
danadena1960 Registered User Join Date: Aug 2003 Location: Stockbridge, GA (Suburbs of Atlanta) Posts: 126	Hello, I did replace the relay, that is what in my opion got it fired up again. My El Camino use to eat them up all the time, why, I have no idea. Now it is a heater delete car. I did not know about the fuse though, I will look into that. How about the switch, have you ever heard of them going bad? Thank you very much for the info., Dana __________________ Dana 77 K-20 454 73 SS El Camino 454 68 SS Camaro 327 48 Chevy 216 755 John Deere

02-25-2004, 12:06 PM	#5
danadena1960 Registered User Join Date: Aug 2003 Location: Stockbridge, GA (Suburbs of Atlanta) Posts: 126	Thank you very much, I will check it out. Thanks again for the infor. Dana __________________ Dana 77 K-20 454 73 SS El Camino 454 68 SS Camaro 327 48 Chevy 216 755 John Deere

02-25-2004, 02:36 AM	#2
NeCrOmAnCeR Registered User Join Date: Feb 2004 Location: Hodgenville, Ky Posts: 735	Be sure to check the relay. High speed bypasses the resistor block entirely. Look at the evaporator box in the engine compartment near the resistor block. You will find a metal relay. Be sure to check the connections to it and the inline fuse for it also. (all located near the evap). If the blower cuts out in the max A/C position also, this is the cause.

02-25-2004, 11:50 AM	#4
NeCrOmAnCeR Registered User Join Date: Feb 2004 Location: Hodgenville, Ky Posts: 735	Yes, they do go bad. Just wanted to make sure that the easy things were checked first. If you wiggle the switch I'd expect the blower to work intermitantly since you stated that the blower will act up when hitting bumps. The inline fuse is between the relay and terminal block where the relay draws power. Mine is a 74 GMC, I think the 77's were similar. The spring in the fuse holder on mine had gotten hot and collapsed, which caused intermitant contact with the fuse. Good luck.



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