A/C Compressor will not engage unless jumped at the relay
- Thread starter heuster
- Start date
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Hamfisted
Full Access Members
The Navi DATC test is the same.
Key - ON / AC - OFF
Push the OFF and FLOOR buttons simultaneously / Release and push the AUTO button within 2 seconds of release.
Let head unit run through it's test ( 30 sec ) .
Note code displayed ( B-code ).
If no faults all digits will illuminate. Press DEFROST to exit test or reset system.
Ford HVAC DATC Self Test Procedure
.
Key - ON / AC - OFF
Push the OFF and FLOOR buttons simultaneously / Release and push the AUTO button within 2 seconds of release.
Let head unit run through it's test ( 30 sec ) .
Note code displayed ( B-code ).
If no faults all digits will illuminate. Press DEFROST to exit test or reset system.
Ford HVAC DATC Self Test Procedure
.
I've tried this in every combination. Key on, engine off AC off.
OFF button and then "mix door" button that adjusts floor, normal, windshield level pushed together and then I hit the "Auto" button. This just results in the AC fan coming on and nothing shows up on the display, the fan just blows.
I figured this out after some searching. It's the Off+Defrost and then the Auto button that kicks off the diagnostics. 00-73 is the code that shows up. I'll do some research and see what that means. If anyone knows off the top of your head, please let me know.
It looks like this is just a transmission code that I saw in ForScan as well. No other codes flash on the display besides 00 73. Anyone with any thoughts on next steps?
Last edited:
DieselMonk
Well-Known Member
You are saying when you jump 30 to 87 at the relay, the system works and blows cold? Make yourself an incandescent test light jig, using some tail light bulb that draws a couple of amps. Then shove that into the relay coil drive on the fuse box and test 85 & 86.
Not sure on exactly how to do what your describing. I have the light, I probably have enough wire, but I'm not sure I understand where to stick the wires.
Also, what results mean what? If the light comes on based on your test, what will that mean?
DieselMonk
Well-Known Member
You switched out the relay and got the same issue. Test the relay coil with you DMM for resistance. You get anywhere from 50 - 200 ohm resistance, your relay coil is good inside the relay itself.
What you didn't check was #85 and 86 that drives the relay coil properly in the fuse box (maybe a pin corroded off etc.). A test light (depending on what brand) may not give you the answer you want, because it isn't drawing enough current. Check the relay coil drive on the fuse box under load.
Test 86 with that 2A light bulb (brake light) jig against battery - or GND. Light should be bright. The 85 you can test with just your test light you already had to positive and turn on the AC switch.
In cars / trucks the 12v is always there once the key switch is turned on... the GND to 85 is what is getting switched in and out (left floating) to drive the coil from a small MOSFET inside some module.
Watch that vid: https://www.youtube.com/watch?v=F5qTf15PKcI&t=11s
Either 86 has no good power, or there is something wrong with 85 getting GND switched in to drive the relay coil. (For that you need a schematic diagram for your car and see where what goes and through what connector(s) and chase it backwards. Its not very hard. Throwing the parts cannon at it is getting boring at this point. Good luck!
What you didn't check was #85 and 86 that drives the relay coil properly in the fuse box (maybe a pin corroded off etc.). A test light (depending on what brand) may not give you the answer you want, because it isn't drawing enough current. Check the relay coil drive on the fuse box under load.
Test 86 with that 2A light bulb (brake light) jig against battery - or GND. Light should be bright. The 85 you can test with just your test light you already had to positive and turn on the AC switch.
In cars / trucks the 12v is always there once the key switch is turned on... the GND to 85 is what is getting switched in and out (left floating) to drive the coil from a small MOSFET inside some module.
Watch that vid: https://www.youtube.com/watch?v=F5qTf15PKcI&t=11s
Either 86 has no good power, or there is something wrong with 85 getting GND switched in to drive the relay coil. (For that you need a schematic diagram for your car and see where what goes and through what connector(s) and chase it backwards. Its not very hard. Throwing the parts cannon at it is getting boring at this point. Good luck!
Ty Ty for the reply!! I really appreciate you taking the time. I will try and get this tested this weekend. I'm not great with schematics so I'll do my best here to get some meaningful results.
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