AC system help

[KilgoreTrout]

The AC kicks on in Defog mode to reduce humidity. With out functional AC, the Defog will work the same as any truck without AC to begin with.

I guess I never really thought about it, but it makes sense.
My 90 Civic that I put like 200k on had a separate switch for AC, though. Maybe it ran even when the light said it was off?
My truck doesn't have ac, but hopefully I can fix that.

 

[bucket]

I guess I never really thought about it, but it makes sense.
My 90 Civic that I put like 200k on had a separate switch for AC, though. Maybe it ran even when the light said it was off?
My truck doesn't have ac, but hopefully I can fix that.

It's just how GM usually (maybe always?) did it. Other manufacturers have done it too, but I've never paid attention to how common it is.

My '00 Burb runs it with the Defog, but the AC button doesn't light up.

 

[KilgoreTrout]

It's just how GM usually (maybe always?) did it. Other manufacturers have done it too, but I've never paid attention to how common it is.

My '00 Burb runs it with the Defog, but the AC button doesn't light up.

Now you really got me wondering about this, and which of my cars did or didn't run it automatically. Lol....
I found the manual for my Mazda, and it says you can choose to run the AC on defrost "if dehumidified drying is desired, turn on the air conditioner".
And "for maximum defrosting, turn on the air conditioner".
I've just always run defrost on full heat/fan without ac, and it worked regardless of whether or not I even had AC.
Now that you mention it, though, I think my Jeeps would run the compressor in defrost mode regardless.
Guess it doesn't matter.

Speaking of ac, though, my compressor doesn't run. I'm assuming no r12 and the pressure switch won't let it?
Is there an easy way to bypass that just to see if it tries to run?
I'll admit that ac systems certainly aren't my thing.
I've removed them and charged them, but that's the end of my knowledge with them.

 

[75gmck25]

The low pressure switch is screwed into the metal tube coming out of the evaporator housing under the hood on the passenger side. Just unplug the round rubber plug (about 50 cent piece size, with two green wires) that is on top and you will see two female spade terminals inside the plug. If you use a short wire with spade terminals to jumper them it should turn on the compressor in A/C position even if pressure is low.

Most US manufacturers automatically turn on the A/C in defrost mode. They don't really document it well because most folks never read manuals anyway, but its usually somewhere in the owners manual. Some foreign cars still control A/C with a separate pushbutton, so you can turn it on in any mode. I think this dates back to the days when A/C was a dealer-installed option in many Japanese cars.

The other feature these trucks have in most years is that when you turn the A/C to Max it will both go into recirculate mode (two vacuum doors change mode) and turn the blower on high. On my '75 its more obscure because Max A/C mode is controlled by the temp slider. When the mode slider is in A/C position, as you slide the temp control far left there is a detent just short of full cold. This is normal A/C. As you slide it all the way to the left it goes to Max A/C. There is no Max A/C position shown for the mode slider.

Bruce

 

[Backfoot100]

Agree with everyone else here. I had a 81 Olds Cutlass diesel that I know ran the AC compressor when in defrost. The manual stated it.

Another thing that nobody has mentioned yet is that the vent windows are wonderful for helping to defrost the windscreen, even without AC.
Other than manufacturing cost and extra wind noise because they seal like crap, the best thing ever that should still be made today.

 

[KilgoreTrout]

The low pressure switch is screwed into the metal tube coming out of the evaporator housing under the hood on the passenger side. Just unplug the round rubber plug (about 50 cent piece size, with two green wires) that is on top and you will see two female spade terminals inside the plug. If you use a short wire with spade terminals to jumper them it should turn on the compressor in A/C position even if pressure is low.

Most US manufacturers automatically turn on the A/C in defrost mode. They don't really document it well because most folks never read manuals anyway, but its usually somewhere in the owners manual. Some foreign cars still control A/C with a separate pushbutton, so you can turn it on in any mode. I think this dates back to the days when A/C was a dealer-installed option in many Japanese cars.

The other feature these trucks have in most years is that when you turn the A/C to Max it will both go into recirculate mode (two vacuum doors change mode) and turn the blower on high. On my '75 its more obscure because Max A/C mode is controlled by the temp slider. When the mode slider is in A/C position, as you slide the temp control far left there is a detent just short of full cold. This is normal A/C. As you slide it all the way to the left it goes to Max A/C. There is no Max A/C position shown for the mode slider.

Bruce

Good stuff, Bruce, thanks!

 

[KilgoreTrout]

Agree with everyone else here. I had a 81 Olds Cutlass diesel that I know ran the AC compressor when in defrost. The manual stated it.

Another thing that nobody has mentioned yet is that the vent windows are wonderful for helping to defrost the windscreen, even without AC.
Other than manufacturing cost and extra wind noise because they seal like crap, the best thing ever that should still be made today.

I love vent windows, too.
Especially back when I used to smoke.

 

[SquareRoot]

Whoa! Let's take a step back because I have a question.

1. How do you know the compressor clutch is bad?

Based on his comment on "the thing in front of the pulley is loose" makes me suspect may not know how it works.

Without the ign on, a/c in cool mode and sufficient r12 in the system its supposed to be loose because it won't engage. Just saying...

 

[C10MixMaster]

Whoa! Let's take a step back because I have a question.

1. How do you know the compressor clutch is bad?

Based on his comment on "the thing in front of the pulley is loose" makes me suspect may not know how it works.

Without the ign on, a/c in cool mode and sufficient r12 in the system its supposed to be loose because it won't engage. Just saying...

look at the pic the clutch is so bad i doesnt even line up with the pulley

 

[SquareRoot]

look at the pic the clutch is so bad i doesnt even line up with the pulley

Ahh, fair enough. I was just doing a little "quality control" check of this thread. Lol

 

[KilgoreTrout]

The low pressure switch is screwed into the metal tube coming out of the evaporator housing under the hood on the passenger side. Just unplug the round rubber plug (about 50 cent piece size, with two green wires) that is on top and you will see two female spade terminals inside the plug. If you use a short wire with spade terminals to jumper them it should turn on the compressor in A/C position even if pressure is low.


Bruce

I jumped the switch and the compressor ran.
It didn't sound all that healthy, but it ran.
I bought 3 cans of r12 on my way home from work, too.
Trying to decide if I should try to charge it.

 

[thecantaloupeman]

Ahh, fair enough. I was just doing a little "quality control" check of this thread. Lol

Well my clutch is bad as well and has no belt. Is that why my defog won't work? Nothing happens when I touch the climate control button. Maybe my blower fan is just disconnected?

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