Need advice on electrical problem...please.
Thread Starter
Le Mans Master
Joined: Mar 2005
Posts: 7,631
Likes: 11
From: Rocklin California
Need advice on electrical problem...please.
Ok, I have Vintage A/C and a Holley Idle solenoid that works fine with 12 Volts. Problem is I can't get the 12 volts from either the compressor or the blower switch that turns the A/C system on. Both only are putting out 10 volts at idle. I haven't checked any other electrical parts. Any ideas? I am a total idiot when it comes to electrical. But I can check voltage. 
Drifting
Joined: Oct 1999
Posts: 1,676
Likes: 494
From: Corrales NM
Ken. If you check your alternator output it should be about 13.8 to 14.2 volts. This is basically the voltage being applied to your electrical system.
The voltage you read at the compressor and blower switch is a function of an voltage drop through the wiring, connectors and contacts. Each one of those components has resistance and the voltage drop is a function of the amount of current flowing through all the components.
If 10 volts is not sufficienct at the input to the solenioid then you will need to trace the wiring back and find where the voltage drops are occuring. You may find one wire, connector or switch contributing a to a significant portion of the drop. I cannot recall how much work you have done to the wiring system in your car but if a lot of it is original it would be easy to drop 3 volts along the way. You may find 10 volts is sufficient for your solenoid and that it is within the accepted voltage range for proper function.
The voltage you read at the compressor and blower switch is a function of an voltage drop through the wiring, connectors and contacts. Each one of those components has resistance and the voltage drop is a function of the amount of current flowing through all the components.
If 10 volts is not sufficienct at the input to the solenioid then you will need to trace the wiring back and find where the voltage drops are occuring. You may find one wire, connector or switch contributing a to a significant portion of the drop. I cannot recall how much work you have done to the wiring system in your car but if a lot of it is original it would be easy to drop 3 volts along the way. You may find 10 volts is sufficient for your solenoid and that it is within the accepted voltage range for proper function.
Race Director
Joined: Nov 2000
Posts: 10,343
Likes: 668
From: Beverly Hills (Pine Ridge) Florida
It would appear that your alternator is not putting out sufficient voltage/current for you "system" at idle (too much load for the alternator), or you have a significant voltage drop.
You will need to verify that if you only have 10 volts at the compressor or blower, then you only have 10 volts at the battery and alternator (not good), so follow NeverL8's directions first. These voltage readings all need to be done while the blower is operating at full speed and the compressor clutch powered "on" (with the engine running at idle).
The other possible problem is the wire gauge is not sufficient to carry the load current for those items (compressor and blower). I can understand the blower drawing a high load and seeing a significant voltage drop, but the compressor wire is only engaging the compressor clutch and should not be a high draw. The compressor wire would be the normal location to connect the idle speed solenoid.
Plasticman
You will need to verify that if you only have 10 volts at the compressor or blower, then you only have 10 volts at the battery and alternator (not good), so follow NeverL8's directions first. These voltage readings all need to be done while the blower is operating at full speed and the compressor clutch powered "on" (with the engine running at idle).
The other possible problem is the wire gauge is not sufficient to carry the load current for those items (compressor and blower). I can understand the blower drawing a high load and seeing a significant voltage drop, but the compressor wire is only engaging the compressor clutch and should not be a high draw. The compressor wire would be the normal location to connect the idle speed solenoid.
Plasticman
Last edited by Plasticman; Jun 14, 2009 at 01:53 PM.
Race Director
Joined: Nov 2000
Posts: 10,343
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From: Beverly Hills (Pine Ridge) Florida
Certainly, if it is not charging properly.
But take the various voltage readings first. Also take DC voltage readings at the alternator and the battery without the blower and AC on (with just the engine running at idle and no other loads.
Plasticman
But take the various voltage readings first. Also take DC voltage readings at the alternator and the battery without the blower and AC on (with just the engine running at idle and no other loads.
Plasticman
Thread Starter
Le Mans Master
Joined: Mar 2005
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From: Rocklin California
Race Director
Joined: Nov 2000
Posts: 10,343
Likes: 668
From: Beverly Hills (Pine Ridge) Florida
Racer
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From: PASADENA CALIFORNIA
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Safety Car
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From: Grosse Ile MI
Plenty juice. Follow what NEVERL8 suggested and also make sure the blower switch and compressor have a good ground. Because of the current draw in that circuit from the compressor clutch and the blower motor, you may have to install a relay to energize the idle solenoid.
Dave
Thread Starter
Le Mans Master
Joined: Mar 2005
Posts: 7,631
Likes: 11
From: Rocklin California
Ken,
Plenty juice. Follow what NEVERL8 suggested and also make sure the blower switch and compressor have a good ground. Because of the current draw in that circuit from the compressor clutch and the blower motor, you may have to install a relay to energize the idle solenoid.
Dave
Plenty juice. Follow what NEVERL8 suggested and also make sure the blower switch and compressor have a good ground. Because of the current draw in that circuit from the compressor clutch and the blower motor, you may have to install a relay to energize the idle solenoid.
Dave
Thread Starter
Le Mans Master
Joined: Mar 2005
Posts: 7,631
Likes: 11
From: Rocklin California
Ken. If you check your alternator output it should be about 13.8 to 14.2 volts. This is basically the voltage being applied to your electrical system.
The voltage you read at the compressor and blower switch is a function of an voltage drop through the wiring, connectors and contacts. Each one of those components has resistance and the voltage drop is a function of the amount of current flowing through all the components.
If 10 volts is not sufficienct at the input to the solenioid then you will need to trace the wiring back and find where the voltage drops are occuring. You may find one wire, connector or switch contributing a to a significant portion of the drop. I cannot recall how much work you have done to the wiring system in your car but if a lot of it is original it would be easy to drop 3 volts along the way. You may find 10 volts is sufficient for your solenoid and that it is within the accepted voltage range for proper function.
The voltage you read at the compressor and blower switch is a function of an voltage drop through the wiring, connectors and contacts. Each one of those components has resistance and the voltage drop is a function of the amount of current flowing through all the components.
If 10 volts is not sufficienct at the input to the solenioid then you will need to trace the wiring back and find where the voltage drops are occuring. You may find one wire, connector or switch contributing a to a significant portion of the drop. I cannot recall how much work you have done to the wiring system in your car but if a lot of it is original it would be easy to drop 3 volts along the way. You may find 10 volts is sufficient for your solenoid and that it is within the accepted voltage range for proper function.
Drifting
Joined: Oct 1999
Posts: 1,676
Likes: 494
From: Corrales NM
Ken,
You have a significant voltage drop somewhere. The voltage drop is just the current through the device times the resistence of the device. If you have a high resistence point like a switch contact, splice, connector, high resistence piece of wire, etc. then the volatage will drop across each one of these.
Methodically trace the wiring from the output of the alternator to the carb solenoid you to find your problem. Measure the voltage using the chassis ground as you negative return point. I am not saying this will be easy, the electrical stuff is always the most difficult for me even though I am an electrical engineer.
You have a significant voltage drop somewhere. The voltage drop is just the current through the device times the resistence of the device. If you have a high resistence point like a switch contact, splice, connector, high resistence piece of wire, etc. then the volatage will drop across each one of these.
Methodically trace the wiring from the output of the alternator to the carb solenoid you to find your problem. Measure the voltage using the chassis ground as you negative return point. I am not saying this will be easy, the electrical stuff is always the most difficult for me even though I am an electrical engineer.
Thread Starter
Le Mans Master
Joined: Mar 2005
Posts: 7,631
Likes: 11
From: Rocklin California
Ken,
Plenty juice. Follow what NEVERL8 suggested and also make sure the blower switch and compressor have a good ground. Because of the current draw in that circuit from the compressor clutch and the blower motor, you may have to install a relay to energize the idle solenoid.
Dave
Plenty juice. Follow what NEVERL8 suggested and also make sure the blower switch and compressor have a good ground. Because of the current draw in that circuit from the compressor clutch and the blower motor, you may have to install a relay to energize the idle solenoid.
Dave
Here is what I ended up doing and also with help from Roy!
After finding out with my original wiring I was not getting a full 12 volts to the solenoid I took a different route. I decided to use a 30 amp relay and 30 amp in-line fuse to get the 12 volts needed. I used the a/c blower switch which turns on my Vintage a/c and wired it to the relay. Then wired the relay to the battery positive cable nut with a 30 amp fuse between the battery and relay. Grounded the relay and ran the last wire to the solenoid. The thing works perfect and I get full voltage at idle which opens the solenoid. The compressor still cycles but my rpm stays right at 600-700 rpm. Ain't it great when something actually works!
Thread Starter
Le Mans Master
Joined: Mar 2005
Posts: 7,631
Likes: 11
From: Rocklin California
totally, and I will have to re-wire the car some day. I didn't feel like creating a bigger problem chasing wires right now and I know there are some repaired wires that need replacing so maybe next winter a new harness?
