New Member, Need AC Advice Please
Thread Starter
Heel & Toe
Joined: May 2024
Posts: 15
Likes: 5
From: Laurinburg NC
New Member, Need AC Advice Please
Hello everyone, new member here, hoping for some advice, I recently purchased my first Corvette, 1999 C5 Convertible, I am having some ac issues and wanted to see if anyone could share some help. The ac compressor will only kick on with a jumper wire on the relay block in the under hood fuse panel, when the wire is jumped the AC light on the dash controls is and stays on and the ac is nice and cold, the ac compressor runs great, once I remove the jumper wire the ac compressor kicks off and the ac light on the controls begins to blink a few times, then goes completely out and the ac begins to get warm. Has anyone experienced this issue or have any insight that may help? Thanks in advance for your assistance.
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Welcome to the forum and moving this to the C5 Tech section for some assistance.
Thread Starter
Heel & Toe
Joined: May 2024
Posts: 15
Likes: 5
From: Laurinburg NC
I'm jumping the AC clutch relay, I have a new relay ordered, however I won't get it for a few days so I was trying to get ahead and see if there is any other issues I should be looking at in the meantime. Thanks
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Thread Starter
Heel & Toe
Joined: May 2024
Posts: 15
Likes: 5
From: Laurinburg NC
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,621
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From: Cape Coral, Florida
Hello everyone, new member here, hoping for some advice, I recently purchased my first Corvette, 1999 C5 Convertible, I am having some ac issues and wanted to see if anyone could share some help. The ac compressor will only kick on with a jumper wire on the relay block in the under hood fuse panel, when the wire is jumped the AC light on the dash controls is and stays on and the ac is nice and cold, the ac compressor runs great, once I remove the jumper wire the ac compressor kicks off and the ac light on the controls begins to blink a few times, then goes completely out and the ac begins to get warm. Has anyone experienced this issue or have any insight that may help? Thanks in advance for your assistance.
You first need to check for HVAC codes and if you jumper the load side of the relay and AC blows cold you have to look at pins 85 and 86 of the relay…you need to check those 2 “control” terminals…could be a bad input such as the ambient temp or AC pressure sensor…a scan tool will help read those data PIDS…you can use a 12 volt test light to see if terminal 85 is being grounded by the PCM if those inputs are OK…wrap some thin copper wire around pin 85 of the relay and reinsert the relay…with test light connected to B+ run the engine and see if the test light illuminates when touching the tip of the test light to the copper wire when pushing the AC button…terminal 85 is the rear terminal closest to the fender….can remember we had a member who had a bad ground on the AC pressure sensor….if PCM can’t read the correct voltage terminal 85 will not be grounded…just swap AC Clutch relay with the horn relay…relays can be installed in ANY direction to work if you don’t know that…also make sure you don’t have any HVAC trouble codes as some will prevent the AC from working…erase them before testing one being a P1545.
Last edited by C5 Diag; May 29, 2024 at 09:08 PM.
Pro
Joined: Dec 2014
Posts: 683
Likes: 275
From: Cincinnati Ohio
Hello everyone, new member here, hoping for some advice, I recently purchased my first Corvette, 1999 C5 Convertible, I am having some ac issues and wanted to see if anyone could share some help. The ac compressor will only kick on with a jumper wire on the relay block in the under hood fuse panel, when the wire is jumped the AC light on the dash controls is and stays on and the ac is nice and cold, the ac compressor runs great, once I remove the jumper wire the ac compressor kicks off and the ac light on the controls begins to blink a few times, then goes completely out and the ac begins to get warm. Has anyone experienced this issue or have any insight that may help? Thanks in advance for your assistance.
Racer
Joined: May 2009
Posts: 253
Likes: 38
From: Austin Tx
A system with low low-side press will blow really cold, then the evaporator freezes over and there's no more airflow.
Side-note: I haven't seen a low-side press sensor in the elec diagrams, only a high-side sensor.
Burning Brakes
Joined: Jun 2018
Posts: 756
Likes: 172
From: SC
Hello everyone, new member here, hoping for some advice, I recently purchased my first Corvette, 1999 C5 Convertible, I am having some ac issues and wanted to see if anyone could share some help. The ac compressor will only kick on with a jumper wire on the relay block in the under hood fuse panel, when the wire is jumped the AC light on the dash controls is and stays on and the ac is nice and cold, the ac compressor runs great, once I remove the jumper wire the ac compressor kicks off and the ac light on the controls begins to blink a few times, then goes completely out and the ac begins to get warm. Has anyone experienced this issue or have any insight that may help? Thanks in advance for your assistance.
Thread Starter
Heel & Toe
Joined: May 2024
Posts: 15
Likes: 5
From: Laurinburg NC
Thread Starter
Heel & Toe
Joined: May 2024
Posts: 15
Likes: 5
From: Laurinburg NC
Thanks everyone,
Hello everyone, new member here, hoping for some advice, I recently purchased my first Corvette, 1999 C5 Convertible, I am having some ac issues and wanted to see if anyone could share some help. The ac compressor will only kick on with a jumper wire on the relay block in the under hood fuse panel, when the wire is jumped the AC light on the dash controls is and stays on and the ac is nice and cold, the ac compressor runs great, once I remove the jumper wire the ac compressor kicks off and the ac light on the controls begins to blink a few times, then goes completely out and the ac begins to get warm. Has anyone experienced this issue or have any insight that may help? Thanks in advance for your assistance.
Thread Starter
Heel & Toe
Joined: May 2024
Posts: 15
Likes: 5
From: Laurinburg NC
Thanks!
You first need to check for HVAC codes and if you jumper the load side of the relay and AC blows cold you have to look at pins 85 and 86 of the relay…you need to check those 2 “control” terminals…could be a bad input such as the ambient temp or AC pressure sensor…a scan tool will help read those data PIDS…you can use a 12 volt test light to see if terminal 85 is being grounded by the PCM if those inputs are OK…wrap some thin copper wire around pin 85 of the relay and reinsert the relay…with test light connected to B+ run the engine and see if the test light illuminates when touching the tip of the test light to the copper wire when pushing the AC button…terminal 85 is the rear terminal closest to the fender….can remember we had a member who had a bad ground on the AC pressure sensor….if PCM can’t read the correct voltage terminal 85 will not be grounded…just swap AC Clutch relay with the horn relay…relays can be installed in ANY direction to work if you don’t know that…also make sure you don’t have any HVAC trouble codes as some will prevent the AC from working…erase them before testing one being a P1545.
Heel & Toe
Joined: Sep 2005
Posts: 18
Likes: 1
From: North Port, Fl
AC not coming on
I checked the ground terminal in pressure sensor plug and shows no grounding. Is that terminal always grounded ignition on or off?
I did check the grounding of the relay and it does not go to ground when turning on the AC. You have to jumper to have the compressor turn on.
when you jumper the relay socket the in side AC control panel will function with fan speed and AC on light stays on.
This is on a 2001 C5