Please help with AC troubleshooting

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Sentra04
Posts: 3
Joined: Wed May 27, 2020 2:20 pm
Car: 2004 Nissan Sentra 1.8s

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Greetings,

I am hoping someone here can offer some insight to finally find a solution to my ongoing AC problem. I have a 2004 Sentra (~80K miles and runs great) that has been without adequate AC for about 2 years. The issue is that the vent temperature never gets very cold. I have run a number of tests with a high quality/accurate probe inserted in one of the center vents, with the AC turned all the way to cold and the fan on full blast, logging every minute for a minimum of 30 minutes under city and highway driving. For city driving, 3 tests, the vent temperature has gone down to 80F (ambient 94F), 77F (ambient 90F) and 70F (ambient 86F). One test on the highway produced 65F (ambient 90F). An observation I have made, and shown in testing, is if the car sits still (parked, stop light, etc.) the temperature climbs. If I am moving, and the faster I go, the temperature drops.

Below is a list of what work has been done on the AC system by my mechanic. I want to give credit to my mechanic as all of their other work has been impeccable and their honesty in cost and need of work (even doing some free fixes just to get me going for a bit longer before needing to bring the car in for further work). Also, my mechanic is determined to fix this issue and has put in at least 15 hours, over multiple sessions, of free labor trying to tackle this (my car's AC issue has become a bit of a white whale for him).
  • Replace AC Suction Hose, Recharge
  • AC Evaporator
  • Expansion Valve & Drier
  • AC Compressor (done with no labor charge)
  • AC Condenser and Drier Assembly (at a discount)

Some additional information that may help:
  • One thing to note is that the replacement evaporator was aftermarket (OEM not available) so brackets were fabricated and install due to a slight difference in size.
  • Pressures are always spot on when I take the car back home and when I return it and the AC lines (cold/hot) in the engine compartment show expected temperatures when measured with an IR temperature gun.
  • On a related note, if I start the car with the AC off and then turn the blower knob to full blast I sometimes hear a "clunk" sound. Of course I have never been able to reproduce this with my mechanic present.

If anyone has any insights or questions please let me know. I am in Florida and it is starting to get brutal with the humidity.


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AZhitman
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Posts: 71061
Joined: Mon Apr 29, 2002 2:04 am
Car: 58 L210, 63 Bluebird RHD, 64 NL320, 65 SPL310, 66 411 RHD, 67 WRL411, 68 510 SR20, 75 280Z RB25, 77 620 SR20, 79 B310, 90 S13, 92 SE-R, 92 Silvia Qs, 98 S14.
Location: Surprise, Arizona
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I'm sure the mech has already checked this, but sounds to me like insufficient airflow through condenser.

Clean the fins with detergent and flush well, make sure there's nothing between the radiator and condenser. Also, ensure condenser fan(s) are engaging, and that they're not spinning the wrong way (sounds crazy, but I've seen it).

Clunk sound could be AC compressor engaging, OR, if the sound is in the cabin, could be the air blend door.

Sentra04
Posts: 3
Joined: Wed May 27, 2020 2:20 pm
Car: 2004 Nissan Sentra 1.8s

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AZhitman,

Thanks for chiming in. I have sent my mechanic a link this this thread. I will be taking the car in tomorrow for some work and another attempt to fix the AC issue and will have him double check the items in your suggestions.

If anyone else has any insight please let me know. I will report once I get the car back and tested. Thanks.

User avatar
AZhitman
Administrator
Posts: 71061
Joined: Mon Apr 29, 2002 2:04 am
Car: 58 L210, 63 Bluebird RHD, 64 NL320, 65 SPL310, 66 411 RHD, 67 WRL411, 68 510 SR20, 75 280Z RB25, 77 620 SR20, 79 B310, 90 S13, 92 SE-R, 92 Silvia Qs, 98 S14.
Location: Surprise, Arizona
Contact:

Post

I have another [offline] source saying it sounds like a blend door issue (which also fits your symptoms).

If the heater and AC air are mixing, you'll see those issues - there may be something about the ambient pressure at the cowl (at freeway speeds) closing the blend door somewhat, giving you a few degrees cooler mix.

Keep us posted, this is good stuff!

Sentra04
Posts: 3
Joined: Wed May 27, 2020 2:20 pm
Car: 2004 Nissan Sentra 1.8s

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Long over due update. I had the shop take another look and they did a few things. Added more foam to seal things up and bypassed the heater core (they also checked all doors, pressures, possible leaks, etc - nothing suspect). Bypassing the heater core was to see if any appreciable difference would happen and it did help a bit but nowhere near where I would like it especially with the current temperatures we are experiencing. I have an airbag recall to take care of so I may let the dealership (yes, I know) take a look at it.

Thanks for your help AZhitman but I am starting to come to terms with the fact that this is just the way it will be until I get a new vehicle.


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