AC high speed fan puzzle-non AC Burb conversion

[70GreenBurb]

I just installed a factory four seasons air system in my 70 non AC Burb. A fan speeds worked for a week or so and then the high speed quit working. Low and Medium still work. I read a few posts and tried a few troubleshooting ideas and just raised more questions.

The high speed relay clicks when the switch is place in high position, but no fan.

When I pull the black ground wire with SW in High, the fan comes on but at a low speed, which seems in between low and Med.

When I pull the Ground wire from the relay with SW in High position, fan comes on low, and then when I try to jumper from the the relay ground post to Battery (-), the relay clicks and the fan stops.

The wiring harness is used but the system worked perfectly (although not as effective as I would like) for a week or so.

Other info;
replaced A6 compressor with a new 10 cylinder compressor
replaced POA valve with new cycling valve
Expansion valve and receiver/dryer are new
Converted from R12 to 134a

Any ideas on what caused High speed to stop working?

[Daddy'O]

Is your relay new or used? Is the relay properly grounded?

Old relay? Could have gone bad.

Bad grounded relay? Relay will not function.

The relay is what controls the high speed for your blower motor.

[70GreenBurb]

Relay is used but it was working. I checked to see if it was energizing and it sounds like it is. I tried a direct to negative ground and the results are in original post. What would be a definitive test? I don't want to troubleshoot by replacing parts that may be good.
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[70GreenBurb]

Well, I have been trying some replacement troubleshooting. I had an extra used fan switch and another used relay. The switch only worked on low so I probably need to clean up the contacts but with I switched the relay, it worked on all positions but in the the high speed position the fan only blows at low speed, similar to what happens when I REMOVE the ground wire from the original relay. Any ideas?

[RichardJ]

I don't know anything about what you are calling "factory four seasons air system" nor could I find a wiring diagram for any '70 AC system.

I found what I was looking for on the '73 and up truck with AC and it is the same as other GM cars of that era. Some Fords too.

The blower is supplied by a separate 12 Volt line with its own in-line fuse for high speed fan operation only. The fuse in the fuse panel supplies 12 volts for the lower speeds, the AC operation and the heater.

If there is a large Red or Orange wire feeding that relay, follow it back into the harness.

[70GreenBurb]

Thanks for the reply. Four Seasons Air was the option name for the factory in-dash air conditioning option for 67-72. GM couldn't just call it air conditioning. I removed the parts from several donor trucks & installed them in my non-AC vehicle. I had read in forums other than 67-72 about an in- line fuse but I didn't see a fuse indicated in the simplified schematic in the factory assembly manual. I did order a new relay so I hope that is the problem. If not, I will open up the harness and look for a fuse. Any idea in what sectio of the harness it might be in? I hope this picture doesn't end up too small to be useful but it is a diagram from the assembly manual.
http://m1254.photobucket.com/albumvi...2.jpg.html?o=0
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[FLEET72]

This diagram was originally posted by fixit-p in this thread. Perhaps it could be helpful to you.

[rfsnyder]

I too was having the Heater/AC High Speed Fan issue… Until last night!!

I’ve read through every “heater fan” thread that I could find. For the most part all the issues that I read, naturally revolved around the Switch, the Resistor, and/or the Relay. I did pull the complete truck electrical schematics from various sources within this site and found that everything is right on the money, except for the Fan connection for A/C enabled trucks. The diagram posted by FLEET72 (from FIXIT-P) is close.. but mine didn’t have the extra Relay labeled “Anti-something”? FIXIT-P posted a different diagram without this extra Relay… and it’s much more appropriate to my setup.. hopefully yours as well.

70GreenBurb – after reading through this thread again.... I really didn’t see that you got your answer. And this is the most recent post on the HIGH SPEED FAN ISSUE, so I’d thought I post a reply on how I fixed mine….

I have a 72 Blazer, with A/C. I rebuilt the switch and purchased a new Resistor and Relay… but was still not getting a High Speed Fan. I only had the low and medium… I did hear the Relay “clicking” during High Speed.. and got the same issue as you when grounded and not grounded.. no speed and slow speed. So something else was amiss… It was the thick 12 gauge orange wire… what is it supposed to do?.. no voltage, nor continuity when with relay was engaged and not engaged. After reviewing the schematic supplied by FIXIT-P it dawned on me… It is another full time power source from the Cigarette lighter circuit. The relay needs two power sources! So to check, I jumped the hot 16 gauge Orange wire (single connector - which is hot when in high speed mode) over to the 12 gauge orange wire… and walla, I had High Speed!! After that, it was just a matter of locating the CIG wire at the fuse box and verify power and continuity back to the relay. I’m good to go now! Hopefully this helps you as well!

[jjzepplin]

OK. So I am having this exact same issue rfsnyder. Exactly the same system. I jumped the motor and it has high capabilities. The relay is new and appears to function. So you are saying you had bad contact with the "cig" wire? Was it at the fuse connection or on the back of the fuse block? Just check for continuity?

[rfsnyder]

Yes check continuity from fuse box to the end of the wire... both sides of the fuse as well. Make sure you are also getting voltage... full-time/continuous 12v... the cig. lighter is a full time hot... always powered.

If you're not getting a continuous hot then trace your leads, check your fuse, or even check the source outside the firewall. Remember both leads need power (12OR and 18OR in diagram) for high speed fan.... so check both leads.

You could run a new line directly, from another full time source... but make sure it's fused and not overloading that circuit. The Cig circuit is ideal though, so try to work that out first.

[jjzepplin]

You are the man! I had a bad contact at the fuse. All looked good but a little rust made its way onto the fuse. AWESOME flow now. Woohoo!