2000 Jeep Grand Cherokee with A/C problem.
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Here is a list of tools I use every day at the shop. Let me know if you use them too in the comments!
General Information:
This 2000 Jeep Grand Cherokee(4.0 liter engine) came into the shop with a complaint of no A/C. The customer said they just had the engine replaced and the air conditioning has not worked since.
First Thoughts:
Many issues can occur with an automotive air conditioning system. A few problems that happen are:
The system is low on freon.
A component has failed, like a compressor.
There could be a wiring issue.
What is interesting to me, is that someone put an engine in this vehicle and then it stopped working. It’s possible that the problem was caused by the person that installed the engine.
Diagnostics:
My first step when diagnosing an air conditioning issue is starting the vehicle to see if the A/C is trying to operate. What I look for is the A/C compressor engaging, the cooling fans turning on, and of course, if the inside air is getting cooler.
In this case, the compressor was not engaging, which indicates two possible diagnostic routes I can take.
The first route would be to check if the system is low on freon.
Automotive A/C systems have pressure sensors in them and when the system is low on freon, it will not operate the A/C compressor.
The shop where I work has an A/C machine that can recover and fill freon into a vehicle. I decided to let the machine recover the freon that is in the Jeep to see if it is a the correct level.
To my surprise, the freon was filled to the correct level.
This test leads me to my next diagnostic route.
The second route would be to see if the A/C compressor is getting the correct voltage and ground to operate.
The A/C compressor has to have a power and ground to turn on. A mixture between the different sensors, commands by the computer, and commands by the driver(the A/C button on the dash) determine when the A/C compressor receives the power to turn on.
The first measurement I need to take is at the A/C compressor’s connector. The connector has two pins. One for a ground and one for positive.
I use my Power Probe 3 and discover that the connector has a ground, but does not have power.
The problem is the A/C compressor is not getting power.
Why would the A/C compressor not have any power?
Here are some reasons why the A/C compressor wouldn’t be getting any power.
A broken wire.
A failed relay
A blown fuse.
With my relay tester on the vehicle, I can see that the relay has power and ground for the relay to turn on, it has power to send to the A/C compressor, and it is working properly.
The last test I can do is a visual inspection to see if there is a broken wire.
If the relay is sending power and the A/C compressor is not receiving power, then there has to be a broken wire.
Right behind the A/C compressor is a group of wires that go very close to the exhaust manifold.
Of course, there really should not be any wires going close to the exhaust without proper heat shielding and this group of wires only has a plastic wire loom.
Closer inspection reveals the broken wire!
It looks like when the engine was replaced, the wires to the A/C compressor were not routed the correct way. The exhaust had burned it in two.
After repairing the wire, the A/C worked great and the Jeep was given back to its owner!
Fixed!
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