A/C Control without ISC

cewrx7r1 · 06-12-2008, 03:13 PM

Non ISC A/C Idle Control

Due to various factors, some of us could not use the ISC for idle control. If we still wanted to use our A/C, we normally had to bump the idle up high under no load in order to prevent the engine from dying under load.
My no load idle was about 1300 rpm. Under full A/C and electric load it would drop to about 950 rpm which was my desired rpm.

There are two ways to partially fix this problem, both use an air control solenoid to increase air flow but only when the A/C is on. The control circuit for the A/C turns on the A/C relay which applies +12 VDC through a refrigerant pressure switch to the pump's magnetic engaging clutch. The ground side of this pressure switch can be used to turn on the new control solenoid only when the A/C is working.

Method 1

Use the old AWS solenoid with it being controlled by the above method. Some form of air flow limiter might be required to restrict the idle from being too high. This can be a pill or manually controlled valve. The input pipe would have to be ducted to either the original source of air on the TB elbow or to another source. Make sure it is filtered.

Method 2

Use a separate solenoid for air control. I have a modified UIM and TB which would not allow me the use of Method 1. I purchased a new 12 VDC solenoid. It is mounted to where the ISC and double throttle controls use to be. It uses the large purge control pipe from the front of the UIM for output into the UIM. I had already disabled the fuel tank vapor purge system many years ago. The source of air is a fitting on the bottom of my Greddy elbow which is also the pressure source for my boost controller solenoid.

Other Info

The new solenoid has about a 1.4 amp power drain, a resistance of about 10 ohms, and was made to work up to 250 psi. I experimented to discover that it could work fine with 15 ohms of extra serial resistance which then limited the amperage to about .6 amps. I installed the resistor onto the A/C drier bracket which is near the refrigerant pressure switch.

I was already using a Hobbs pressure switch to turn off the A/C when boost went over 2 psi. It is placed between the ground side of the refrigerant pressure switch and the A/C pump coil. Thus if either the refrigerant pressure drops too low or boost goes over 2 psi, my A/C will turn off and the solenoid will not increase idle speed.

Results

I have my base idle adjusted for 950 rpm with only full electric load which increases to about 1000 rpm with no loads. With the A/C on, idle is about 1050. With full A/C and electric load, idle is about 1000 rpm.

PICS AT:

New Solenoid
http://i192.photobucket.com/albums/z...1/Solenoid.jpg

Hobbs Switch
http://i192.photobucket.com/albums/z...x7r1/Hobbs.jpg

06-12-2008, 03:13 PM	#1
cewrx7r1 The Judge Join Date: Feb 2008 Posts: 196 Rep Power: 18	A/C Control without ISC Non ISC A/C Idle Control Due to various factors, some of us could not use the ISC for idle control. If we still wanted to use our A/C, we normally had to bump the idle up high under no load in order to prevent the engine from dying under load. My no load idle was about 1300 rpm. Under full A/C and electric load it would drop to about 950 rpm which was my desired rpm. There are two ways to partially fix this problem, both use an air control solenoid to increase air flow but only when the A/C is on. The control circuit for the A/C turns on the A/C relay which applies +12 VDC through a refrigerant pressure switch to the pump's magnetic engaging clutch. The ground side of this pressure switch can be used to turn on the new control solenoid only when the A/C is working. Method 1 Use the old AWS solenoid with it being controlled by the above method. Some form of air flow limiter might be required to restrict the idle from being too high. This can be a pill or manually controlled valve. The input pipe would have to be ducted to either the original source of air on the TB elbow or to another source. Make sure it is filtered. Method 2 Use a separate solenoid for air control. I have a modified UIM and TB which would not allow me the use of Method 1. I purchased a new 12 VDC solenoid. It is mounted to where the ISC and double throttle controls use to be. It uses the large purge control pipe from the front of the UIM for output into the UIM. I had already disabled the fuel tank vapor purge system many years ago. The source of air is a fitting on the bottom of my Greddy elbow which is also the pressure source for my boost controller solenoid. Other Info The new solenoid has about a 1.4 amp power drain, a resistance of about 10 ohms, and was made to work up to 250 psi. I experimented to discover that it could work fine with 15 ohms of extra serial resistance which then limited the amperage to about .6 amps. I installed the resistor onto the A/C drier bracket which is near the refrigerant pressure switch. I was already using a Hobbs pressure switch to turn off the A/C when boost went over 2 psi. It is placed between the ground side of the refrigerant pressure switch and the A/C pump coil. Thus if either the refrigerant pressure drops too low or boost goes over 2 psi, my A/C will turn off and the solenoid will not increase idle speed. Results I have my base idle adjusted for 950 rpm with only full electric load which increases to about 1000 rpm with no loads. With the A/C on, idle is about 1050. With full A/C and electric load, idle is about 1000 rpm. PICS AT: New Solenoid http://i192.photobucket.com/albums/z...1/Solenoid.jpg Hobbs Switch http://i192.photobucket.com/albums/z...x7r1/Hobbs.jpg Last edited by cewrx7r1; 06-12-2008 at 04:23 PM.