Ac and coolant gauge stop working
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Member
Joined: Dec 2025
Posts: 65
Ac and coolant gauge stop working
So I have replaced the ac blower motor and then did the relay and solenoid. Now I’m finding that while driving today my ac shut off along with the coolant gauge. Anyone know the fix on this one?
Senior Member
Joined: Feb 2016
Posts: 121
I have more questions, starting with the year of your H3.
Regarding your AC Shutting Off
When you say that your AC shut off, are you referring to the Blower Motor itself (fan doesn't work), or your AC On/Off button & light fails to engage the AC? If it is the latter, does the temperature control work (rotate the **** and listen for the blend doors to make noise) and the HVAC modes (floor, vent, etc.) work as well?
If your AC Button, temperature control, and modes all three do not work, I would be willing to bet you lost power (orange 12V wire) to the HVAC assembly. You can remove the stereo/HVAC center console panel, disconnect all the wire harnesses, and measure with a multimeter how many volts you are getting to the orange wire that feeds into the HVAC assembly. If you're getting 12V (should be hot at all times), then this is not the issue. If you're getting low/no volts, then you may have to run a separate hot wire to the HVAC assembly to get it back up and running. Again, this is only if the temperature control, AC on/off, and HVAC modes do not work.
For context: when I was replacing the stereo on my wife's H3 alpha, while I was working, I must have crimped/broken/messed up a very old wire (that probably hasn't been moved in almost 20 years) because after I reconnected everything, the HVAC control did not work, which was due to the 12V orange wire somehow failing while I was working and setting up the new stereo. I ended up running a wire from the battery directly to the orange hot wire into the HVAC harness, and the HVAC came back to life.
Coolant Temperature Gauge
There are only two wires that connect to the coolant temperature sensor, both of which run to the PCM. One is a yellow wire, and the other is a black wire which provides the Low Reference Signal from the PCM to the coolant temperature sensor.
1. Try disconnecting the sensor, turn the ignition on, and see how many volts you are getting for the low reference. It should be around 5 Volts.
2. If you're getting 5V at the low reference wire, hook everything back up, heat the car up, connect with a scan tool, and see what the Coolant Temperature is reading on the scan tool. If it's reading normally, yet the gauge still indicates low temperature, then the issue is not in the PCM/coolant temperature sensor, and instead lies somewhere in the gauge/wiring itself. If the scan tool indicates low coolant temperature after the car is heated up, then you need a new coolant sensor.
3. If the issue lies within the instrument cluster itself, then I do not know how you would go about diagnosing this, because the Instrument Cluster gets its (coolant temperature) information from the transfer of serial data from the Body Control Module via the Computer Data Lines system. There is very little data in the Schwartz Schematics that shows exactly how the instrument cluster interprets this data to provide a reading on the temperature gauge. It simply shows that the Coolant Temperature is reliant on "Ignition" and "Serial Data" on the instrument cluster schematic.
Send an update regarding if its your Blower Motor, or the Temperature Control/HVAC Modes/AC on/off, as well as what the voltage is to the 5V low reference wire, as well as what a Scan Tool is reading temperature wise when the engine is heated up.
Regarding your AC Shutting Off
When you say that your AC shut off, are you referring to the Blower Motor itself (fan doesn't work), or your AC On/Off button & light fails to engage the AC? If it is the latter, does the temperature control work (rotate the **** and listen for the blend doors to make noise) and the HVAC modes (floor, vent, etc.) work as well?
If your AC Button, temperature control, and modes all three do not work, I would be willing to bet you lost power (orange 12V wire) to the HVAC assembly. You can remove the stereo/HVAC center console panel, disconnect all the wire harnesses, and measure with a multimeter how many volts you are getting to the orange wire that feeds into the HVAC assembly. If you're getting 12V (should be hot at all times), then this is not the issue. If you're getting low/no volts, then you may have to run a separate hot wire to the HVAC assembly to get it back up and running. Again, this is only if the temperature control, AC on/off, and HVAC modes do not work.
For context: when I was replacing the stereo on my wife's H3 alpha, while I was working, I must have crimped/broken/messed up a very old wire (that probably hasn't been moved in almost 20 years) because after I reconnected everything, the HVAC control did not work, which was due to the 12V orange wire somehow failing while I was working and setting up the new stereo. I ended up running a wire from the battery directly to the orange hot wire into the HVAC harness, and the HVAC came back to life.
Coolant Temperature Gauge
There are only two wires that connect to the coolant temperature sensor, both of which run to the PCM. One is a yellow wire, and the other is a black wire which provides the Low Reference Signal from the PCM to the coolant temperature sensor.
1. Try disconnecting the sensor, turn the ignition on, and see how many volts you are getting for the low reference. It should be around 5 Volts.
2. If you're getting 5V at the low reference wire, hook everything back up, heat the car up, connect with a scan tool, and see what the Coolant Temperature is reading on the scan tool. If it's reading normally, yet the gauge still indicates low temperature, then the issue is not in the PCM/coolant temperature sensor, and instead lies somewhere in the gauge/wiring itself. If the scan tool indicates low coolant temperature after the car is heated up, then you need a new coolant sensor.
3. If the issue lies within the instrument cluster itself, then I do not know how you would go about diagnosing this, because the Instrument Cluster gets its (coolant temperature) information from the transfer of serial data from the Body Control Module via the Computer Data Lines system. There is very little data in the Schwartz Schematics that shows exactly how the instrument cluster interprets this data to provide a reading on the temperature gauge. It simply shows that the Coolant Temperature is reliant on "Ignition" and "Serial Data" on the instrument cluster schematic.
Send an update regarding if its your Blower Motor, or the Temperature Control/HVAC Modes/AC on/off, as well as what the voltage is to the 5V low reference wire, as well as what a Scan Tool is reading temperature wise when the engine is heated up.
Last edited by Spanovich008; Mar 8, 2026 at 03:10 PM.
Thread Starter
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Member
Joined: Dec 2025
Posts: 65
Spanovich008, thank you, that’s was a lot of great info! I have a 09 H3t with the 3.7. Working out a lot of issue as I’ve only had it a couple of months. I literally started driving it this weekend. What had happened is the ac was blowing cold and then just stopped, there was a message on the dash cluster “ac off” and I noticed the coolant gauge was not on. The heater did blow hot but no cold. After a restart all worked fine. I’m guessing I will have this again so wanted to see if anyone had had the same issue. After doing more research I’m thinking it may be the thermostat getting stuck open.
Senior Member
Joined: Feb 2016
Posts: 121
Not a problem at all!
For reference, the schematics I posted are for a 2007 H3, but I’m guessing there aren’t too many massive changes for the 2009 H3T.
With your added context, not to go back on what I said in my previous message, but now I would be willing to bet its something more simple, such as your coolant temperature sensor working intermittently, or one of the two wires that connect from the PCM to the sensor going intermittently bad (in your 2009, the wires should actually be tan and yellow, not black and yellow as found in the 2007).
If the temperature sensor, or one of the wires leading to it fails intermittently, and the PCM cannot determine the engine coolant temperature, the air conditioning will be shut off and you’ll get the AC OFF message.
I would have to dig a little deeper in the schematics themselves, however the Engine Coolant Temperature Sensor is included in the Air Conditioning schematic as well, which leads me to believe there is some kind of logic built in that turns the heat on full hot if the engine coolant temperature signal is erroneous or too hot, in an attempt to help cool down the engine.
Either way, glad to hear that the problem went away after a restart. If the problem gets worse, I’d start with the easiest solution, and replace the coolant temperature sensor (yes you could argue that that is throwing parts at the problem, but those sensors aren’t too expensive). If that doesn’t solve the issue, then I would inspect/measure the resistance in the wires that lead from the PCM to the coolant temperature sensor. Inspect and replace as required.
Based on what you’re telling me, it doesn’t sound like your thermostat is sticking open; even with the thermostat fully stuck open in cool weather, the gauge should still at least register 1/8th-1/4th of a tick mark on the temperature gauge, and it should not initiate an AC OFF message.
okay, I’ll quit blowing up this thread. Keep us updated and let us know what happens! Glad to hear your H3T is officially on the road!
For reference, the schematics I posted are for a 2007 H3, but I’m guessing there aren’t too many massive changes for the 2009 H3T.
With your added context, not to go back on what I said in my previous message, but now I would be willing to bet its something more simple, such as your coolant temperature sensor working intermittently, or one of the two wires that connect from the PCM to the sensor going intermittently bad (in your 2009, the wires should actually be tan and yellow, not black and yellow as found in the 2007).
If the temperature sensor, or one of the wires leading to it fails intermittently, and the PCM cannot determine the engine coolant temperature, the air conditioning will be shut off and you’ll get the AC OFF message.
I would have to dig a little deeper in the schematics themselves, however the Engine Coolant Temperature Sensor is included in the Air Conditioning schematic as well, which leads me to believe there is some kind of logic built in that turns the heat on full hot if the engine coolant temperature signal is erroneous or too hot, in an attempt to help cool down the engine.
Either way, glad to hear that the problem went away after a restart. If the problem gets worse, I’d start with the easiest solution, and replace the coolant temperature sensor (yes you could argue that that is throwing parts at the problem, but those sensors aren’t too expensive). If that doesn’t solve the issue, then I would inspect/measure the resistance in the wires that lead from the PCM to the coolant temperature sensor. Inspect and replace as required.
Based on what you’re telling me, it doesn’t sound like your thermostat is sticking open; even with the thermostat fully stuck open in cool weather, the gauge should still at least register 1/8th-1/4th of a tick mark on the temperature gauge, and it should not initiate an AC OFF message.
okay, I’ll quit blowing up this thread. Keep us updated and let us know what happens! Glad to hear your H3T is officially on the road!
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Joined: Jul 2007
Posts: 13,090
From: Boat Town USA MI
By default, if your PCM cannot confirm engine water temp. it will turn off the AC and display AC OFF in the DIC to avoid overheats.
Means your coolant temp sender is bad, or the harness and/or connector to it are bad. Inspect the wires for compromise, spray CRC Electronic Cleaner on both sides of the connection, let dry, reconnect. If that doesn't do it, plan on a temp sensor change.
Means your coolant temp sender is bad, or the harness and/or connector to it are bad. Inspect the wires for compromise, spray CRC Electronic Cleaner on both sides of the connection, let dry, reconnect. If that doesn't do it, plan on a temp sensor change.
Senior Member
Joined: Jun 2015
Posts: 795
From: SoCal
By default, if your PCM cannot confirm engine water temp. it will turn off the AC and display AC OFF in the DIC to avoid overheats.
Means your coolant temp sender is bad, or the harness and/or connector to it are bad. Inspect the wires for compromise, spray CRC Electronic Cleaner on both sides of the connection, let dry, reconnect. If that doesn't do it, plan on a temp sensor change.
Means your coolant temp sender is bad, or the harness and/or connector to it are bad. Inspect the wires for compromise, spray CRC Electronic Cleaner on both sides of the connection, let dry, reconnect. If that doesn't do it, plan on a temp sensor change.
Junior Member
Joined: Mar 2026
Posts: 4
I?ve had this exact issue. I changed the thermostat and never had the problem again.