Replaced Alternator Now AC Blows Hot Air: What Could Be The Reason

It can be infuriating when you fix one issue in your vehicle, only to have another problem pop up right after. 

This often happens when replacing an alternator – you get the charging system working again, but suddenly, the air conditioning starts blowing hot air. 

There are a few reasons this occurs, but the problem is fixable if you diagnose it properly.

Causes that the A/C Blows Hot Air After Replacing the Alternator

Loose or Disconnected Wiring

• When removing the old alternator, it’s very easy to inadvertently loosen or disconnect wirings that are related to the A/C compressor. 

• Specifically, the wire that activates the compressor clutch is prone to getting into failures. 

• If this happens, the compressor won’t turn on when you switch the A/C on by preventing the cold air flow.

Disturbing Refrigerant Lines

• Suppose any of the refrigerant lines are loosened or disconnected during the alternator replacement. 

• In that case, it can disrupt the flow of refrigerant and cause the A/C to blow hot air. 

• Damaging a refrigerant line can also cause leaks.

Incorrect Reassembly

• If wiring harnesses or refrigerant lines are reconnected incorrectly after installing the new alternator, refrigerant and electrical flow to the A/C compressor may be impacted. 

• Taking photos before disassembly helps to avoid this issue.

Troubleshooting Tips and Fixes for a Hot A/C after the Alternator Replacement

Inspecting the System

• Pop the hood and inspect all wiring, refrigerant lines, and connections to the compressor. 

• Look for loose fittings, damaged components, or disconnected wires. 

• Verify the compressor engages when you turn the A/C on.

Checking Wiring

• First of all, focus on the wiring to confirm that there are no obvious leaks. 

• Use a voltmeter to check for power at the compressor clutch wire. 

• Secure any loose connectors and repair the damaged wires.

Testing the Refrigerant Flow

• If the wiring looks okay, connect the A/C gauge sets to test the refrigerant pressure. 

• Remember that, leaks, blockages, or low refrigerant will require professional recharging and repairs.

Preventing the A/C Disruption During the Alternator Replacement

Photograph Connections

• Carefully note and photograph any wires, hoses, or connectors you remove when taking out the old alternator. 

• Therefore, those can be properly reassembled to overcome some of the issues.

Work Cautiously Around the A/C Components

• Be very careful when pulling the alternator out. 

• Make sure that you don’t put any extra stress on any neighbouring A/C parts and wiring.

Double Check the Work When Finished

• After installing the new alternator, start the vehicle and test the A/C function immediately to identify any issues before wrapping up the repair.

• With care and diligence, you can avoid collateral damage to your A/C system when replacing an alternator. 

• But if hot air starts blowing, methodical troubleshooting of the wiring and the refrigerant flow should get your cold air back soon.

Frequently Asked Questions About Replaced Alternator Now AC Blows Hot Air

Q: How do I reconnect a loose compressor clutch wire?

A: Locate the wire that powers the AC compressor clutch. Make sure the connector at the end is plugged in firmly. Use zip ties to secure the wire so it doesn’t vibrate or loose. Double-check any other wires that may have been disturbed.

Q: Do I need to recharge the AC refrigerant after replacing the alternator?

A: Maybe. If the issue is just a bad connection, recharging the refrigerant is optional. But suppose you identify any leaks or low pressure. In that case, you’ll need a professional to safely restore the system with fresh refrigerant.