a/c questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

tommie · 04-22-2010, 06:14 PM

on my 75' 1/2 ton big block,

blower motor was only working on HI

i replaced the blower resistor, then found out my ac relay on the ac box was bad. (relay working now)

the blower fan speeds work correctly in all ranges (bi-level, defrost, heater, vent etc)

when i have the selector in MAX AC, the blower motor only works on HI speed...

is this normal?

I thought the speed would have been adjustable...

Input please....

tommie · 04-23-2010, 08:45 AM

anyone with factory ac?

tommie · 04-23-2010, 12:49 PM

anyone with an a/c wiring diagram for a 75?

raws67 · 04-23-2010, 06:22 PM

Max a/c just routes air from inside cab and not outside, basically recirculating cab air that is already cooled. Hi speed will be the same either a/c or max a/c. Is it only on max a/c that you cant get med or low fan?

tommie · 04-23-2010, 07:24 PM

yes, only on max ac...

on max ac i only have hi speed...

on all other settings, i have all blower speeds....

never ran into this problem before...

raws67 · 04-24-2010, 02:25 AM

As far as I know there should be no interconnection between the two since vacum control is the only change when going to max a/c. I will check my service manuals in the am and try and get you a diagram of the wiring.

raws67 · 04-24-2010, 03:07 PM

These are from my 74 gmc service manual. Let me know if you need any closer pics. Good luck

tommie · 04-24-2010, 10:11 PM

thanks for the info... now i have to read it all!!!!!

04-22-2010, 06:14 PM	#1
tommie 97' Tahoe 2dr/2wd Join Date: Jul 2002 Location: Huffman,TX Posts: 1,168	a/c questions on my 75' 1/2 ton big block, blower motor was only working on HI i replaced the blower resistor, then found out my ac relay on the ac box was bad. (relay working now) the blower fan speeds work correctly in all ranges (bi-level, defrost, heater, vent etc) when i have the selector in MAX AC, the blower motor only works on HI speed... is this normal? I thought the speed would have been adjustable... Input please.... Last edited by tommie; 04-22-2010 at 06:15 PM.

04-23-2010, 08:45 AM	#2
tommie 97' Tahoe 2dr/2wd Join Date: Jul 2002 Location: Huffman,TX Posts: 1,168	Re: a/c questions anyone with factory ac?

04-23-2010, 12:49 PM	#3
tommie 97' Tahoe 2dr/2wd Join Date: Jul 2002 Location: Huffman,TX Posts: 1,168	Re: a/c questions anyone with an a/c wiring diagram for a 75?

04-23-2010, 06:22 PM	#4
raws67 Registered User Join Date: Jun 2007 Location: lemoore ca Posts: 126	Re: a/c questions Max a/c just routes air from inside cab and not outside, basically recirculating cab air that is already cooled. Hi speed will be the same either a/c or max a/c. Is it only on max a/c that you cant get med or low fan? Last edited by raws67; 04-23-2010 at 06:23 PM.

04-23-2010, 07:24 PM	#5
tommie 97' Tahoe 2dr/2wd Join Date: Jul 2002 Location: Huffman,TX Posts: 1,168	Re: a/c questions yes, only on max ac... on max ac i only have hi speed... on all other settings, i have all blower speeds.... never ran into this problem before...

04-24-2010, 02:25 AM	#6
raws67 Registered User Join Date: Jun 2007 Location: lemoore ca Posts: 126	Re: a/c questions As far as I know there should be no interconnection between the two since vacum control is the only change when going to max a/c. I will check my service manuals in the am and try and get you a diagram of the wiring.

04-24-2010, 03:07 PM	#7
raws67 Registered User Join Date: Jun 2007 Location: lemoore ca Posts: 126	Re: a/c questions These are from my 74 gmc service manual. Let me know if you need any closer pics. Good luck Attached Images

04-24-2010, 10:11 PM	#8
tommie 97' Tahoe 2dr/2wd Join Date: Jul 2002 Location: Huffman,TX Posts: 1,168	Re: a/c questions thanks for the info... now i have to read it all!!!!!

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