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Sentra Nissan Sentra Discussion Forum

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Old 07-21-2019, 06:46 AM
filmteknik filmteknik is offline
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2005 Sentra
2005 Sentra
Join Date: Jul 2019
Location: Suburban Chicago
Posts: 1
Default HVAC blows hot (heated) air

Yesterday a friend bought a 2005 Sentra @ 146K miles. Seemed in decent shape with only minor issues noted. A bit of pulsing on the brakes so maybe warped rotors and a bit of bounce to the ride like worn but not blown shocks.

One thing that pleased us was the nice cold air the A/C was putting out on one of the hottest days of the year.

For the record this is basic HVAC with a hot / cold knob not a temperature setting.

But last night as she was testing various features she turned the control knob to the hot end. It blew hot air as expected. But it kept blowing hot air even turned back to maximum cold (blue).

It doesnít matter how the output knob is set. Weíre sure itís heated air not just non air conditioned.

Any ideas? Did we just have the bad luck to have the HVAC computer fail just hours after buying? Can I replace it?

Further symptoms: Fan blows and speed is still regulated by the fan knob.

A/C and recirc buttons light up when pressed (except fan speed 0 of course.

Iím pretty sure the output control knob is non functional. Think it was properly directing output to different vents before but not 100% certain.

Compressor is clutching in normally.

Have not yet checked the R134A charge. Could low charge make it do this? I understand no cooling but this is actually blowing hot.

I seem to recall that the sellerís CL ad, now gone, mentioned the nice cold AC. If he charged it just for the test drive and itís actually a leaky system and it already dumped the charge I get lack of cooling but not blowing hot and the output knob not working. So I think it points to the computer but what say you all?
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Old 07-23-2019, 04:29 PM
mpe235's Avatar
mpe235 mpe235 is offline
2015 Rogue
Join Date: Jun 2006
Location: New York
Posts: 5,570

Sounds like the cable for the temperature door came loose.
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Old 07-23-2019, 10:22 PM
smj999smj's Avatar
smj999smj smj999smj is offline
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2006 Pathfinder
2003 Frontier King Cab
2003 Frontier KC SVE 4x4
Join Date: Jun 2012
Location: Prospect, VA
Posts: 1,849

If you have manual HVAC, then you likely don't have an "A/C computer. Anything's possible, but I would suspect a bad air mix mode door actuator. As with anything, you have to do the diagnostic steps for the symptom, which are located in the factory service manual for your vehicle. You can access a free, online FSM at Nico Club's site:

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