AC help needed
Thread Starter
Instructor
Joined: Oct 1999
Posts: 182
Likes: 0
From: SW Oklahoma
AC help needed
I have a 72 that will not turn its AC compressor on. I had a gentleman that has been in the AC business a long time work on it and he thinks the only thing it could be is a switch or relay somewhere up under the dash that shows up on the wiring diagram. I bought the switch that is on the consol but the old one seems to work well so I ahve not replaced it. Does anyone know where this other switch or relay is. Sometimes it works sometime it dont. If it does come on it works well and then works normally for a while. If it don't I can put twelve volts to the compressor and it will start and then it may or may not work normally. ANY HELP WOULD BE APPRECIATED!
One more thing what bracket do I need to put headers on this car?
One more thing what bracket do I need to put headers on this car?
Le Mans Master
Joined: Aug 2003
Posts: 7,720
Likes: 12
From: Chattanooga TN
You get 12v to the side of the a/c control with ignition on. With the switch in specific positions you get 12v to the tan wire to the engine compartment thermal switch. If it is above freezing in the outer box then you get 12v to the dark green wire to the compressor.
Check for 12v on the tan wire at the thermal switch. If you have that consistantly then the thermal switch is likely bad. If that is what was already replaced, then you either have a bad wire or problems at the control in the console.
Check for 12v on the tan wire at the thermal switch. If you have that consistantly then the thermal switch is likely bad. If that is what was already replaced, then you either have a bad wire or problems at the control in the console.
Thread Starter
Instructor
Joined: Oct 1999
Posts: 182
Likes: 0
From: SW Oklahoma
when I turn the control switch to AC the fan blows etc etc. When I put it to Max it makes more noise as it should. The thermal switch? Is that the one that has three wires going into it? AC is not one of my strong points-I'd much rather deal with chassis or engine pblms. I will check this tonight and see what gives. If you think of anything else let me know.
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Originally Posted by RLS
when I turn the control switch to AC the fan blows etc etc. When I put it to Max it makes more noise as it should. The thermal switch? Is that the one that has three wires going into it? AC is not one of my strong points-I'd much rather deal with chassis or engine pblms. I will check this tonight and see what gives. If you think of anything else let me know.
Le Mans Master
Joined: Aug 2001
Posts: 7,804
Likes: 4
From: Standing still with all my might Texas
Cruise-In X Veteran
St. Jude Donor '09-'11
If the 72 system is the same as the 73 you will have a thermal switch in the AC evaporator box, on the outboard side near blower motor.
It has two wires going to it and operated by sensing the the temperature of the air entering the evaporator core. Any temp about ~32degrees F the circut is closed, below ~32 F the switch opens and shuts off the power to the compressor clutch.
You can test this switch with a multimeter. There should be continuity across the terminals at room temperature; then stick it in the freezer for a few minutes and check it again, there should be no continuity until it warms up above freezing.
There is also what I am pretty sure is a pressure switch in the back of the compressor with one wire going to it. I don't know how you would go about testing it though.
Also check all the electrical terminals at each of these switches for corrosion, oil and dirt. You might just have a bad connection.
It has two wires going to it and operated by sensing the the temperature of the air entering the evaporator core. Any temp about ~32degrees F the circut is closed, below ~32 F the switch opens and shuts off the power to the compressor clutch.
You can test this switch with a multimeter. There should be continuity across the terminals at room temperature; then stick it in the freezer for a few minutes and check it again, there should be no continuity until it warms up above freezing.
There is also what I am pretty sure is a pressure switch in the back of the compressor with one wire going to it. I don't know how you would go about testing it though.
Also check all the electrical terminals at each of these switches for corrosion, oil and dirt. You might just have a bad connection.
Le Mans Master
Joined: Aug 2003
Posts: 7,720
Likes: 12
From: Chattanooga TN
Originally Posted by Kevin_73
If the 72 system is the same as the 73 you will have a thermal switch in the AC evaporator box, on the outboard side near blower motor. It has two wires going to it and operated by sensing the the temperature of the air entering the evaporator core. Any temp about ~32degrees F the circut is closed, below ~32 F the switch opens and shuts off the power to the compressor clutch.
You can test this switch with a multimeter. There should be continuity across the terminals at room temperature; then stick it in the freezer for a few minutes and check it again, there should be no continuity until it warms up above freezing.
You can test this switch with a multimeter. There should be continuity across the terminals at room temperature; then stick it in the freezer for a few minutes and check it again, there should be no continuity until it warms up above freezing.
Originally Posted by Kevin_73
There is also what I am pretty sure is a pressure switch in the back of the compressor with one wire going to it.
Thread Starter
Instructor
Joined: Oct 1999
Posts: 182
Likes: 0
From: SW Oklahoma
Hey Hey Hey Christmas has come early!!!!! After a short 2 hour looksey I finally found the problem. Thanks to all who helped! You all made sense of the wiring of the AC and that helped with the wiring chart. You do not know how this has stumped me for some time. What it was the blower/compress switch in the consol! I had ordered that part several years ago but decided it did not need it at that time. I wish I had changed it then. Anyway changed it out and cold air--just in time for winter! Thinking more about it I had read in a manuel that you had to pull the consol out. The factory manuel said you did not and I "got her done"! Thanks to all that helped out. Now to find out what the rumbling in the rear is. I hope it aint bearings!
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