AC Compressor Problem
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From: Bryan Texas
AC Compressor Problem
Howdy, working on an 89 with electronic AC controls. I get 12 volts to the compressor when the key is on, doesn't matter if the ac controls are on or not. I don't have ground though.
My main question is how the compressor is switched.. is the 12 volts switched on and off or the ground?
I've cleaned the ground on top of the frame by the passenger exhaust manifold, jumped the 2 pressure switches and whatever that little switch is by the pressure switch on the high side hard line. When I jump a ground to the compressor, it works, but never shuts off unless I turn the key off.
When I got the car, the radio harness was pretty well molested, maybe something going to the ac controls got butchered too?
Thanks
My main question is how the compressor is switched.. is the 12 volts switched on and off or the ground?
I've cleaned the ground on top of the frame by the passenger exhaust manifold, jumped the 2 pressure switches and whatever that little switch is by the pressure switch on the high side hard line. When I jump a ground to the compressor, it works, but never shuts off unless I turn the key off.
When I got the car, the radio harness was pretty well molested, maybe something going to the ac controls got butchered too?
Thanks
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From: Bryan Texas
thanks.. freon is good, just filled it up.. blows cold. The wires to the compressor are giving me fits... The ground wire has no ground and the 12 volts is on all the time the key is on. I'm off to check the blower control module.. if I can find it.
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 42
From: Baltimore, MD USA
The Blower control module enables the AC clutch by grounding the Dark Green
wire. If you ground that wire the Blower control module has no control
of the clutch.
Here's the schematic.
When AC is requested by the control head, if the high pressure cut off switch and low pressure cycling switch are closed, it sends a signal on the Dark Green/Yellow wire at the Blower control module which is located inside the evaporator housing You'll see two electrical connectors on top of the housing that plug into the blower control module.
The Blower control module will ground the Clutch Dark Green wire. The control head also sends a signal to the ECM to increase the idle speed.
wire. If you ground that wire the Blower control module has no control
of the clutch.
Here's the schematic.
When AC is requested by the control head, if the high pressure cut off switch and low pressure cycling switch are closed, it sends a signal on the Dark Green/Yellow wire at the Blower control module which is located inside the evaporator housing You'll see two electrical connectors on top of the housing that plug into the blower control module.
The Blower control module will ground the Clutch Dark Green wire. The control head also sends a signal to the ECM to increase the idle speed.
Last edited by Hooked on Vettes; May 21, 2011 at 07:31 PM.
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From: Bryan Texas
ok, thanks.. and thanks for the diagram.
I found that the compressor ground wire goes back to the blower control module, but it's not grounded there either, but at least it's a good wire.
I'll check my pressure switches. I also discovered that there is no compressor clutch diode that I can see. I've read that it can mess up the blower control module if it doesn't have a diode. I believe we have it narrowed down pretty well.
Thanks again,
Mike
I found that the compressor ground wire goes back to the blower control module, but it's not grounded there either, but at least it's a good wire.
I'll check my pressure switches. I also discovered that there is no compressor clutch diode that I can see. I've read that it can mess up the blower control module if it doesn't have a diode. I believe we have it narrowed down pretty well.
Thanks again,
Mike
Racer
Joined: Dec 2003
Posts: 277
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Does it shut off if you disconnect the low pressure cycling switch? my 88 had a similar situation and I replaced the LP switch and it cleared it up. My compressor ran even with the completly system empty. It was a $11. switch at Autozone. You can replace it w/o discharging the system.
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Thread Starter
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Joined: Oct 2006
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From: Bryan Texas
Mine won't turn on unless I jump/ground the blower control module wire to the compressor. I believe either the blower control module is bad, or pressure switches aren't telling it to turn on the compressor.
I tried jumping the switches at their harness connections, one at a time and found no joy. I kinda think the blower control module is bad, but I'll keep playing with it tomorrow, may evein take the blower control module apart and see what I can see.
I tried jumping the switches at their harness connections, one at a time and found no joy. I kinda think the blower control module is bad, but I'll keep playing with it tomorrow, may evein take the blower control module apart and see what I can see.
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 42
From: Baltimore, MD USA
When you turn the AC on, the voltage level on the Dark Green/Yellow wire at the blower control module should be around 6 volts. If there is no voltage change and the engine idle speed doesn't increase something is wrong with the control head. (Since you verified the cycling switch and high pressure switch are closed). Try re-seating the electrical connector on the back of the control head. Look at the 2 electrical plugs at the blower control module for signs of corrosion or heat problems.
Last edited by Hooked on Vettes; May 22, 2011 at 01:22 AM.
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From: Bryan Texas
I pulled the control head, unplugged it and plugged it back in, now I'm getting 7.2 volts at the blower control module, still no ground going to the compressor.. sure sounds like the blower control module, huh?
Also, there is an unplugged connector under the control head, I'll post a pic to see if anybody recognizes that rascal.
Also, there is an unplugged connector under the control head, I'll post a pic to see if anybody recognizes that rascal.
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 42
From: Baltimore, MD USA
With the engine not running I measure about
5.5 volts on the Dark Green/Yellow wire when
the AC is ON. When AC is off it's 0.0 volts.
Also the clutch does engage when the engine is
not running.and AC is ON. (You can't turn the clutch plate).
Turn AC off and you can turn the clutch plate.
If you grounded the Dark Green wire at Connector C1
(the connector that has the Dark Green wire and the Red wire
which is 12 volts hot at all times from a fusible link) and ignition
ON and the clutch engages, the blower control module must be bad.
Only other thing to verify is Connector C2 Black wire is
making a good connection to ground. (Blower control module
ground).
The 4 pin connector looks like it's used by the Bose radio.
5.5 volts on the Dark Green/Yellow wire when
the AC is ON. When AC is off it's 0.0 volts.
Also the clutch does engage when the engine is
not running.and AC is ON. (You can't turn the clutch plate).
Turn AC off and you can turn the clutch plate.
If you grounded the Dark Green wire at Connector C1
(the connector that has the Dark Green wire and the Red wire
which is 12 volts hot at all times from a fusible link) and ignition
ON and the clutch engages, the blower control module must be bad.
Only other thing to verify is Connector C2 Black wire is
making a good connection to ground. (Blower control module
ground).
The 4 pin connector looks like it's used by the Bose radio.
Thread Starter
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From: Bryan Texas
ok.. with 6.5 volts now at the blower control module compressor signal wire, I get no ground to the compressor. Jumping a ground to the compressor ground wire at the connector at the blower control module, the compressor clutch engages. I took the blower control module apart and found no serviceable parts other than cleaning the connection prongs, which did no good. I aslo jumped from the big black wire at the blower control module to the compressor ground wire at the blower control module and the compressor clutch engaged. So, I'm looking for a blower control module.
Thanks Hooked for guiding me though this.
Thanks Hooked for guiding me though this.
Last edited by myk7; May 22, 2011 at 07:52 PM.
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 42
From: Baltimore, MD USA
Delco 1572530 over $100 new.
http://frugalmechanic.com/auto-part/...elco&t=1572530
There's a used one on E-bay with a warranty for $40 shipped.
http://cgi.ebay.com/ebaymotors/86-89...item2563ebf7a9
http://frugalmechanic.com/auto-part/...elco&t=1572530
There's a used one on E-bay with a warranty for $40 shipped.
http://cgi.ebay.com/ebaymotors/86-89...item2563ebf7a9
