'72 - Air Condition (AC) Question
Thread Starter
Instructor
Joined: May 2007
Posts: 118
Likes: 0
From: Michigan
'72 - Air Condition (AC) Question
Just got my car back from storage and my AC quit working. Here's what I checked.
I jumpered +12 VDC to the compressor - it came on and blew cold.
With power jumpered to the compressor so that it's on, I check the low-side pressure and it was good. I checked the AC fuse in the fuse box and it is good. This seems to say that the AC is good but it's just not getting power.
This seems to leave only the switch in the counsel or the wire going to the compressor.
Any idea what might be wrong here?
I jumpered +12 VDC to the compressor - it came on and blew cold.
With power jumpered to the compressor so that it's on, I check the low-side pressure and it was good. I checked the AC fuse in the fuse box and it is good. This seems to say that the AC is good but it's just not getting power.
This seems to leave only the switch in the counsel or the wire going to the compressor.
Any idea what might be wrong here?
Burning Brakes
Joined: Jun 2008
Posts: 1,086
Likes: 1
From: Michigan
Bypass the high pressure switch near the compressor and see if it comes on. If it does, it might mean that the charge is low and the switch is protecting the system. My '73 has a ambient temperature switch that prevents the compressor from coming on if the temp is below 59*F. It's still colder than that in Michigan right now 
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Follow the wire from the compressor clutch back toward the firewall. Some years had a thermal limiter- little rectangle box in-line with that wire. It was sort of a fuse thing that died on a regular schedule.
Burning Brakes
Joined: Jun 2008
Posts: 1,086
Likes: 1
From: Michigan
BTW...the compressor will only run if the blower motor is at least in low mode which should be all the time. If the blower motor won't run, neither will the compressor.
Racer
Joined: Mar 2005
Posts: 487
Likes: 0
From: Jacksonville FL
Thermal limiter fuse
http://www.napaonline.com/MasterPage...l+Limiter+Fuse
if your system is low, this fuse will just blow again. mite want to have it looked at.
good luck,
Mike.
http://www.napaonline.com/MasterPage...l+Limiter+Fuse
if your system is low, this fuse will just blow again. mite want to have it looked at.
good luck,
Mike.
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Thread Starter
Instructor
Joined: May 2007
Posts: 118
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From: Michigan
Mike,
I was just going to upload a photo to confirm that was it! Thanks.
If I unplug the thermal limiter fuse and check voltage to the socket, I do not measure any power on any of the 3 pins. Shouldn't I measure power on at least one of them with the AC on? Is there a way to ohm this part out to check it (I have to get my hands on a schematic as I don't have one at the moment)?
I also see that the compressor has a line coming off the back of it (black w/ yellow stripe). Do you (or anyone) know if this is a low pressure switch? If it is, what monitors this line and cuts power if it is low? It this also done in the thermal limiter fuse?
I was just going to upload a photo to confirm that was it! Thanks.
If I unplug the thermal limiter fuse and check voltage to the socket, I do not measure any power on any of the 3 pins. Shouldn't I measure power on at least one of them with the AC on? Is there a way to ohm this part out to check it (I have to get my hands on a schematic as I don't have one at the moment)?
I also see that the compressor has a line coming off the back of it (black w/ yellow stripe). Do you (or anyone) know if this is a low pressure switch? If it is, what monitors this line and cuts power if it is low? It this also done in the thermal limiter fuse?
Last edited by fdunford; Apr 24, 2009 at 07:34 PM.
Racer
Joined: Mar 2005
Posts: 487
Likes: 0
From: Jacksonville FL
With your ac turned on, you should measure 12 volts between the outer two sockets in that three socket plug that you pulled the thermal limiter out of. The center socket goes to that black with yellow wire coming off of the back of your compressor and yes that is the low pressure sensor. It sends a signal and blows the thermal limiter (which is basically a fuse) when your system is low on Freon.
If you have no power at that plug with your system on, the problem must be further back up the line. Start working back from that point using a good wiring diagram until you find out why you have no power.
Good luck, because electrical problems can be a lot of fun. (NOT!)
Mike.
If you have no power at that plug with your system on, the problem must be further back up the line. Start working back from that point using a good wiring diagram until you find out why you have no power.
Good luck, because electrical problems can be a lot of fun. (NOT!)
Mike.
Thread Starter
Instructor
Joined: May 2007
Posts: 118
Likes: 0
From: Michigan
Mike,
Its further back as I have no power on any of the 3 pins at the thermal limiter fuse.
I now have both a oOSOEZ print and AIM manual (neither of them have a clear schematic of the circuit but its the best info I can find).
What works: Blow motor at all speeds (rules out resistor pack), thermal switch, thermal limiter fuse, compressor (when jumped - 45psi).
I am suspecting the AC Relay. Does anyone know what the AC Relay circuit looks like?
For the AC Relay there is 1 connector for ground, and a 2nd connector with 3 wires. When the AC is on, the Orange (power in from Horn Relay) measures +12, the Purple (Blower Motor power) measures +12, but the Blue (Blower Motor switch) measure 0. Do you or anyone know if the blue wire should have +12 when the system is on? I am thinking it should, but am not sure how to verify.
I'm open to all suggestions...
Its further back as I have no power on any of the 3 pins at the thermal limiter fuse.
I now have both a oOSOEZ print and AIM manual (neither of them have a clear schematic of the circuit but its the best info I can find).
What works: Blow motor at all speeds (rules out resistor pack), thermal switch, thermal limiter fuse, compressor (when jumped - 45psi).
I am suspecting the AC Relay. Does anyone know what the AC Relay circuit looks like?
For the AC Relay there is 1 connector for ground, and a 2nd connector with 3 wires. When the AC is on, the Orange (power in from Horn Relay) measures +12, the Purple (Blower Motor power) measures +12, but the Blue (Blower Motor switch) measure 0. Do you or anyone know if the blue wire should have +12 when the system is on? I am thinking it should, but am not sure how to verify.
I'm open to all suggestions...
