1970 Corvette 350ci/350hp: AC Cuts OFF when fan is switched to med and high?
A good friend of mine owns a 1970 corvette coupe 350ci/350hp with AC. The predicament he is experiencing is when he turns on the AC with fan in low speed it blows cold air, when he switches to medium or high speed the AC cuts off. In the reverse situation when the heater is running this does not happen, she blows hot in all fan speeds. The fan switch was replaced but to no avail, the same scenario as above occurs. Could this problem be with relay switche(s)? Are there distinctive relay switches associated with the AC/ fan control and if so where are they located? Or could this be a different problem altogether? I would appreciated any advise you can render to solve this situation....and make me look good at the same time!!!
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Re: 1970 Corvette 350ci/350hp: AC Cuts OFF when fan is switched to med and high?
I had this happen with my 69 recently, but only for the high speed setting. Turns out the points on the High speed relay needed to be filed a bit. Relay is located int he engine compartment on the outside of the blower box. Take it off, upen both ends, clean the points and put it back together. Took about 15 minutes. -
Re: 1970 Corvette 350ci/350hp: AC Cuts OFF when fan is switched to med and high?
Terry is right and if that high speed fan relay is bad, both A/C and heat will not blow on high.
JeffComment
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Re: 1970 Corvette 350ci/350hp: AC Cuts OFF when fan is switched to med and high?
Gene,
Can you clear up something for me.
All blower speeds work fine when it is heat alone? Yes or No
You say " when he turns on the AC with fan in low speed it blows cold air, when he switches to medium or high speed the AC cuts off." Do you mean the fan cuts off, or the A/C compressor cuts off?
MonteComment
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Re: 1970 Corvette 350ci/350hp: AC Cuts OFF when fan is switched to med and high?
Monte; All Blower speeds work fine when in Heat Mode.....When in AC mode in low fan AC works fine , when he switches to medium/high speed fan the AC compressor unit cuts off?Comment
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Re: 1970 Corvette 350ci/350hp: AC Cuts OFF when fan is switched to med and high?
Gene.
It sounds like the compressor switch is bad. The compressor switch is part of the Heat/Cool Control panel.
The switch itself cannot be gotten to without taking the shifter plate off. Once the plate is off you will see where all the small hoses collect on the left side of the controller. About 1" forward, 1" down, and 1" outward, or closer to the drivers leg there are two sets of contacts under controller case.
Before removing anything else, just forward of the circle of small hoses you will see a plug pointing backwards or towards the rear of the car. It is sticking out from under the top of the controller case.
It should have three wires connected to two terminals. A light green and a gray on one terminal and a tan on the other. I think those are the colors.
Anyway, to test the switch, unplug that plug by pulling toward the front of the car. Once you have the plug in hand, put a jumper from one side to the other.
After the jumper is in try the A/C and fan then.
If I did not explain this very well you can find the "Comp SW" or compressor switch on a wiring diagram. The switch is part of the controller when you pull it out on its little frame.
To remove the switch, on the outside of the controller case on the left side just forward of the circle of small tubes there are two 1/4" head screws you can see from the outside. They are the only ones in that area. Remove those two screws and a set of points will fall out.
That is all these switches are is a set of contacts that float out there with nothing covering them except on the top by the controller case.
I hope this helps a bit. but it should do the job.
Remember: After the shifter plate is off, you will have access to the plug. You may just see the wires sticking out, but the plug is just under the left side of the controller case itself.
Best of luck,
MonteComment
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Re: 1970 Corvette 350ci/350hp: AC Cuts OFF when fan is switched to med and high?
Gene,
A little revision. When the shifter plate comes off, the small hoses and the flug will actually still be under the front lip of the opening where the plate was.
So, you will have to slide the controller toward the rear a bit, or better yet, just turn the whole thing counter clock wise a bit. You just might see that plug.
I know this is a big job and you may want to see if any one else chimes in with an easier fix, but I think it just might be that switch.
As was mentioned before, there are two relays for fan speeds. Low speed is its own beast and even has its own power source.
I just looked at the high speed relay side and wondered what would it take to stop the compressor, and at the same time be able to run everything in heat mode.
Only one contact set fit the bill. Let's keep our fingers crossed if you do decide to challenge this.
MonteComment
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Re: 1970 Corvette 350ci/350hp: AC Cuts OFF when fan is switched to med and high?
Gene,
After looking at everything again, I am not sure it is that set of points or not.
I just bring it up because I do not want you tearing into a car until I can go over it again.
I resolved it earlier today. I did it again later this afternoon before I posted my reply.
Now, I am sitting here second guessing my thought process. I will look at it a bit more in the morning with a fresh set of eyes and let you know what I come up with.
If the car is still apart from replacing the switch as you mentioned in your initial post, then this would not be much work to test out.
But, if the car is all back together, it is quite a bit of work and I would hate to see you go through all that knowing there might be something wrong with my assessment of the situation.
Get back with you tomorrow.
MonteComment
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Re: 1970 Corvette 350ci/350hp: AC Cuts OFF when fan is switched to med and high?
Gene,
Have you had any luck?
I cannot remember how the fan switch terminals change with each movement. I know on of them activates terminal #6 which is a clue to this.
When I get home this evening I will dig out one ofmy NOS fan switches and double check the terminal sequence. I think this will help with the problem.
Is there anything else you can think of to tell me. It is not making sense. One more little clue might just solve this very easily.
I know you already mentioned this, but the A/C compressor AND the fan quite working when he puts the fan speed in med or high.
Also, he does have and A/C fan switch in there with 6 terminal and not the Heat switch with 4 terminals? Correct.
The wrong fan switch would cause something very close to this situation.
MonteComment
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Re: 1970 Corvette 350ci/350hp: AC Cuts OFF when fan is switched to med and high?
Gene,
Can you ask you buddy to clear up something very minor, but very important.
The A/C system in the Corvette, and most production cars for that matter, have a built in safety system so the unit does not freeze up.
When you put the controller to the A/C position, the fan should automatically go on to the low speed without even touching the fan switch. This just tells the system it is pushing freon around and because of that there should be at least a little air flowing across the evaporator coil to prevent it from freezing up.
My question is: When he has turned the A/C control to cool and the fan is running and the fan switch is still on off, it is blowing cool air.
The important question is: Does the fan continue to run when he put the fan on low, or is that when it dies.
If that is when it dies then it is a very easy fix.
If on the other hand it is blowing cold air when the A/C control is in the cool position on the dial and the fan runs while the fan switch is actually in the LOW position ans it shuts off when it is turned the MED-LOW we have a lot bigger problem to solve.
This is what has been throwing me off and I want to make sure it is not shutting off when he turns it to LOW.
I hope I was clear in my request of information. And, I know it is not a non-A/C fan switch because the plug that plugs into the fan is different for each.
Anyone else feel free to chime in if you think it might help.
Best of luck,
MonteComment
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Re: 1970 Corvette 350ci/350hp: AC Cuts OFF when fan is switched to med and high?
Gene,
Bla, bla, bla.
After looking at it again, I think I was wrong. Yes, I was wrong. lol
On the left side of the control panel I described the set of contacts I thought were failing.
Just below that set of contacts, in the same little hollow, there is another set further back. I think that is the set that is failing.
The first set I pointed out I said were facing forward. Sticking straight at the motor. Once again, I was wrong. They faced down toward the tunnel.
The second set I am speaking of face backwards. The actual connectors and the plug will be sticking out of the left side bottom of the control panel. Very easy to see and get to to unplug.
Again, I would jump a wire across the two terminals at the plug itself.
You cannot get the different plugs mixed up if you take them both off because one set is side by side while the other set is over under.
You want the over under set.
These points are very fine and it takes very little to clean them up a bit. A little emmory cloth or anything else that might polish them a bit should do the trick.
If you cannot get them to work, I have a few sets here and I have no problem sending you one. You can buy me a beer next time we run into each other. That is if we ever meet.
Give that a try and let me know what happens. If that does not do it there is one other option I can think of, but we will deal with that if we need to.
Again, best of luck,
MonteComment
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