Good morning
I have an operational question regarding the factory AC in a 1966 small block. The entire system has been rebuilt. I am finding that when the low or medium speed blower fan is selected, using the dash ****, the compressor clutch engages. When high speed is selected the clutch will disengage.
As the **** to activate the AC is pulled on the dash (upper left ****) the clutch will engage and low speed from the blower is activated. As it should and is described in the AIM section C60 sheet E9. When high speed is selected the compressor clutch will stay engaged.
I've attached some photos. One is of the compressor clutch switch under the dash. It is activated when the AC **** is pulled. The yellow wire is the blower low speed from the dash switch, second yellow hidden by my hand holding switch, goes out to the resistor on the blower motor box, brown is 12v power in, and green goes directly to the compressor plug.
Other pictures are of the resistor. Yellow wire is the blower motor low speed coming from the previous picture, light blue is the blower motor medium speed coming from dash selector ****, and dark blue is power that goes to the blower motor relay and in turn makes contact with a purple wire that feeds the blower motor, section C60 sheet E9 again. As a side note, the low and medium speed is bypassed when high is selected on the dash **** as it all goes thru the blower relay where that circuit is protected by an inline 30 amp fuse in a 1966.
Sorry to be so long....but again my question is when low or medium fan blower speed is selected thru the dash **** WITHOUT selecting or pulling the AC dash **** out is the compressor clutch supposed to engage. It seems odd to me that it would....but looking at these pictures and seeing how its wired I don't know how it can't engage as the one green wire from the compressor switch goes directly under the dash and makes contact with low speed yellow wire and is energized the minute low is selected. By proxy when medium speed is selected, I believe the green wire gets energized thru the resistor as the low (yellow) and medium (light blue) speed wires make contact with each other at that location.
Thank you
Cory

Compressor clutch switch...yellow: low speed wire. Green: compressor power. Brown: 12 volt power.

Blower motor resistor mounted passenger side on top of blower housing unit. Yellow: low speed. Light Blue: Medium speed. Dark blue: power to purple wire, thru relay, which powers blower motor.

Resistor

 

Compressor clutch should engage only with AC **** (compressor switch) in which case fan comes on low. I suspect compressor clutch is being backfed. Check your grounds carefully.

Dan

 

Dan
Thanks for the reply..... I thought that would be the case. I checked all grounds for connection. Additionally I ran seperate grounds directly to the battery for the compressor and blower motor. Operates the same. Just replaced the new blower motor relay. Still the same results. I've even eliminated the dash blower switch and used a jumper wire from the brown (12 volt supply) to yellow (low speed) and light blue (medium speed). All with the exact same results.......I've also unplugged the blower motor ground completley just to see what would happen...same result......Low speed on the blower motor **** activated...compressor clutch engages...same thing on medium speed.
Interestingly enough with the blower switch off and the AC **** pulled I know the clutch should engage but instead of the low speed fan coming on, as stated in the AIM, it comes on high speed. If I unplug the the light blue med speed wire and orange high speed wire from the switch then and only then will the low speed fan come on when the AC **** is pulled.......
Cory

 

Cory:

It sounds like you checked out the AC relay and that it was not the problem.........correct??

One thing I noticed from your picture is that your AC compressor ON-OFF switch under the dash/glovebox area appears to be a two prong switch. Originals were three prong. Here is a link to an original. https://www.ebay.com/itm/NOS-GM-62-6...EAAOSwSTFeqzpv

At this point I would probably call Lectric Limited and talk with their service guys and see what they say.

It still may be possible that problem is the ON-OFF switch which is not three prong. Only way to tell is to buy an original or have someone with an original test it for you and report results. You told me you have another switch, but how many connections does it have?? I believe your checks on the INDAK resistor for the blower motor and its electrical connector for cross terminal connections eliminates this as an issue. If the AC relay tests out as we discussed, then it comes back to the ON-OFF switch or a factory incorrect termination on one of the wires.

Larry

 

Corey:

Is that a ZIP AH-253 switch and harness extension?? If so, show me a few more closeups of the switch back and the connector plug. Is the green and yellow wire together in one plug?? If so, then anytime yellow is energized, green will also be energized and visa versa.

Need more pics and info.

Larry

 

Hi Larry
Yes you are correct. That compressor clutch or on off switch under the dash is only 2 prong and the green and yellow wires are together to the same terminal. Thats what I was mentioning in the first post. I don't see how green could not be energized the minute the low speed is selected. I found it odd. I got the part from ZIPS part#AH-253. Its provided to them by Old Air Products of Florida. I have not been able to get thru to them after multiple phone calls today to ask them that very same question you raise. I have been only able to leave a message for a call back.
Thanks again for you time.
Cory

 

Here are the photos. Yellow and green are in the same plug. The 2 yellows seen are the blower switch yellow and the resister yellow. Thats how the new harness came.
Cory



Pigtail unplugged from the switch

 

Then that is the problem. Buy the original switch and connect it per your AIM.

Larry

 

Cory:

I believe that Old Air Products deliberately made the two prong switch and connector wire harness you received. It was not an accident. Initially I assumed that it was all Lectric Limited stuff.

Reason being, the retro air conditioning guys think that just about everyone has AC and uses it constantly. Down here in Deep South Louisiana, the AC on our cars and trucks is never turned OFF. It is always ON. So they made up a wire connector harness and switch that would energize the AC compressor anytime you ran the cabin blower. Forget those guys that want it "like original". LICS offers a reproduction 3-prong switch as original, but cost is about the same as the link to a GM original switch that I provided earlier.

FWIW.........

Larry

 

Larry
That could be but I'm going to share what I learned last night. In speaking with Dom he told me he was a chevy dealer mechanic in the early 70's. He has a 1966 AC service/operation manual given to him by his supervisor. It covers corvette along with some other Chevy models. In it he read to me that the operation was described this way: turning the blower fan on low or medium speed will activate the AC! In order to operate the AC on high, pull the AC **** and with the blower motor switch off. You could also select high on the blower switch with the AC **** pulled out. Apparently the reasoning behind having the AC on at the same time as heat had something to do with reducing humidity or language like that. Dom is going to take a picture of what he found in his dealer manual and send it to me. I'll share it when I see it. He was shocked in reading that.
Initially I was going to make a comment about suppliers selling the right parts but it looks like maybe they know something from research. Coincidently I looked for my old wiring harness and found that exact "original" 3 prong compressor switch attached to the old wiring that you described. Cleaned it off, installed it and all works as I think, or thought it should. AC only operates when the AC dash **** is pulled. Crazy stuff!
Cory

 

Zip part is advertised as for 63-67. I do not believe that 1966 was a special case............but I know for sure that my 1967 factory air car does NOT operate as you just described.

Larry

 

I am unwilling to believe this in the absence of a copy of that Chevrolet directive. Doesn't sound right to me, otherwise they would have done the same across the car lines which they did not. In the 70's most auto HVAC would run refrigeration in defrost mode to aid in clearing fogged glass from a damp interior, not in 60's cars. If I'm wrong I'll give myself 20 lashes.

Dan

 

Agreed....waiting for the copy...