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Discussion Starter · #1 ·
2006 EX 4wd, 105,000 miles, no NAV or REC, all service up to date by Honda dealer since new. Second owner, bought used in 2015 with 28K on the clock.

Over the last two weeks or so, the A/C has slowly gotten weak and only blows warm air front and back; I suspect a leak or perhaps the TXV. After reading numerous other posts here regarding A/C, here are my symptoms and what I've checked so far. No previous A/C work or repairs, system is still factory.

Compressor engages and stays on when A/C is on; both radiator and condenser fans run strong and shut off when A/C is off. The low pressure switch does not disengage the compressor, so I assume I have enough freon to function some. Blower motor works at all speeds; all modes between defrost/feet, etc, also work properly. After a time, condensate begins to drip under the car front and rear, leading me to believe evaporators are functioning but still no cold air. Low pressure line near the low pressure service port never gets cold. I checked the air mixture motor/linkage under the passenger dash and it appears to operate smoothly over the full range from hot to cold. The heater valve control on the firewall also appears to opening/closing with the air mix motor.

I ran the diagnostic for the HVAC circuits from the service manual at 21-78; no DTC's showed up. I also ran the diagnostic for the HVAC sensors from the SM at 21-82; all were in spec with the exception of the Front Air Mix Opening reading. With the temperature setting at max heat, it read 99%, indicating warmer air distribution. With the temperature set at max cool, it read 66%. Could this indicate a stuck flap/door, preventing 100% of the air from being directed to the evaporator?

Next I hooked up a set of manifold gauges to high and low service ports. Temp was 76, humidity at 70. Static pressure was 69 psi on both.(On some of the R134 charts I looked at, I think my static pressure, based on atmospherics, should have been closer to 80 or so. Indicative of a low charge maybe?) Started car and let it reach operating temperature. Hit the A/C and low side dropped down to 8 psi, high side went up to 95 psi. Went through several manual on/off cycles, and the best I could get was 10 psi on the low and 105 psi on the high, which are both well below normal. Pressures did seem to equalize fairly quickly during the off cycles though. I performed only a cursory search for leaks, nothing extensive yet.

Would it be safe to add a bit of freon, without oil or other additives, to the system to get back to normal pressures and see if it holds? Any suggestions or something I overlooked?

Thanks in advance for your help.

FWIW, I'm a semi-expert when it comes to adding freon; my 2000 Blazer, which the Pilot replaced, was addicted to those little white cans for the last two summers of its miserable life...
 

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As a former Blazer owner (1999), I'd say your intended course of action is where I'd start as well.

Keep us posted.
 

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Discussion Starter · #3 ·
Thanks plplplpl.

"I also ran the diagnostic for the HVAC sensors from the SM at 21-82; all were in spec with the exception of the Front Air Mix Opening reading. With the temperature setting at max heat, it read 99%, indicating warmer air distribution. With the temperature set at max cool, it read 66%."

In reference to my above issues, can anyone out there run the same DX on a known working first gen A/C system to give me a baseline/comparison for the Front Air Mix Opening reading on max cold? Simple test, takes all of two minutes.

Again, thanks in advance for the help. Trying to get informed for probable DIY, prior to hitting dealership for quote in the thousands for complete new system.
 

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Discussion Starter · #4 ·
UPDATE:

Ran the sensor DX again this morning, with actual converted values. Ambient temp 84 F, humidity 51%. In-car temp per sensor was 95 F; evaporator output temp, per sensor, was 64-68 F; as expected, about 30 degrees below ambient. Dash vents still about ambient. Air mix door position sensor still showed only 65% at max cold; it read 99% and FO (fully open?) at max heat.

I looked under the dash and watched the air mix control motor go through what seemed to be full range of motion (from interweb video) from hot to cold as thermostat knob was rotated. Could not manually force linkage further towards cold. However, after only three clicks back from full hot towards cold, air mix motor went to full cold, rather than gradually over the range from hot to cold as knob was rotated. Makes me think HVAC control unit is at fault, doesn't know temp request per knob position and still blowing some air over heater core rather than full evaporator.

Ran the DX again tonight at 7 PM; outside air was 90 F, in-car was 93 F. Car was at operating temp, both fans running. Evaporator outlet temp was 70 F, not quite 30 degrees below ambient. Air mix door was at 65%. Haven't run the manifold gauge pressures yet since inital 30 days ago, but that won't tell you you're low on freon.

Called the local Honda dealership, who have performed all manufacturer scheduled maintenance for the last five years on my Pilot; spoke with the service writer and briefly described my issue and requested to speak with an A/C tech. Service writer said they were all busy and I got put on hold; got tired of holding so I hung up. Guess I'll have to go see them in person and throw a fit, I just want a baseline reading on air mix motor position sensor to better diagnose my issue.

Any thoughts?

Thx guys/gals
 

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Discussion Starter · #5 ·
One last sensor DX this morning at 7AM. Outside temp was 62, 86% humidity. Per sensors, cabin temp was 63, outside temp was 70. Evaporator outlet temp started at 43, then rose to 54, settling at 57, not much below ambient. Evaporator still drips condensate. Vent temp was at 52. Checked the air mix door position again; went click-by-click towards max cold, and sure enough at three clicks short of max cold it read 01%; I've ruled out the blend door as the culprit. Video here, (
alternatively, I found placing a hand mirror under it to see it in action much easier than doing a headstand in the floorboard.

I now suspect a weak/failing compressor as the issue, per the SM. Compressor currently stays engaged; that tells me there is enough freon still in the system that the low pressure switch does not trip and disengage clutch. From my original manifold readings, low pressure on both sides and pressure equalization occurring pretty quickly after manual A/C shutoff, leads me to the compressor being the issue. Weekend plan is to add a bit of no-additive freon with the gauges and monitor pressures, but I expect no improvement on cooling if the compressor is indeed the issue.
 

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I appreciate your efforts.. I have a similar situation in my 08. Ac starts off nice and loses its effectiveness over time.. I noticed “steam” coming from the vents this morning in a beam of sunshine.. only it wasn’t steam but like what comes off ice as it sublimes. (Sublimation: Ice turning to vapor while skipping the liquid phase).
 

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Discussion Starter · #8 ·
I appreciate your efforts.. I have a similar situation in my 08. Ac starts off nice and loses its effectiveness over time.. I noticed “steam” coming from the vents this morning in a beam of sunshine.. only it wasn’t steam but like what comes off ice as it sublimes. (Sublimation: Ice turning to vapor while skipping the liquid phase).
Ford Guy-

I would suspect your evaporator is icing up; possibly caused by low freon charge or bad TXV not metering correct amount to evaporator. You can run the simple DX here: 2006 Auto Climate Control Self Diagnostic Procedure? to see what evaporator outlet temp is.

Alternatively, you can remove the glovebox, (simple procedure, search youtube) pull the cabin filter, and actually see what is actually going on with the evaporator. It will be the radiator looking thing immediately downstream, or to the driver's side, of where you pulled the filter. Make sure car is on, up to operating temp, both fans operating under hood, and A/C to max cold.
 

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Discussion Starter · #9 ·
As a former Blazer owner (1999), I'd say your intended course of action is where I'd start as well.

Keep us posted.
Fixed.

Late spring this year 2021, hooked up manifold gauges to A/C, ambient temp was around 90F. A/C system was never open to atmosphere ever. Gauges only showed each high and low about 50 PSI static, which is way below what charts show, potentially indicative of a low refrigerant charge. Both fans still activate, A/C compressor kicks on and stays on, so I know both high and potentially low-pressure cut-off switches are good.

With the A/C on, per ambient temp of 90F, the chart says low side should be around 100-120 PSI (if I remember correctly) and high side should be 220-250 PSI. I only got about 30 on the low side and maybe 100 PSI on the high side with the A/C on, which explains why my A/C wasn't working. (Had to research refrigerants and thermodynamics and my chemistry/physics/etc in college to understand heat transfer)

Unhooked the low side gauge, to make the port available to slowly add refrigerant, but kept high side hooked up to read pressures. Slowly added refrigerant to low side (bought from the big box store, and DO NOT shake the can from side-to side).

I filled the system slowly until high side read 225 or so PSI and then shut her down and unhooked everything. Still don't know what low side reads, but must be within specs, as A/C has worked like a champ all summer long.

Advice-

Do your research, and use reliable gauges to assess your A/C system. Don't rely on a website that says you must only add X amount of refrigerant to your system, lest you blow it up.

The Culprit-

Turns out my problem was a leaky schrader valve on the low side port; maybe common among Honda A/C's.
 

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Discussion Starter · #11 ·
Working now?
Still cooling like a champ. Haven't replaced the schrader valve yet, so I'm sure at some point I'll be low again. Probably let the shop do it when that time comes around again, as I don't currently have the equipment to properly drawn down the system to vacuum and recharge.
 

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The Culprit-

Turns out my problem was a leaky schrader valve on the low side port; maybe common among Honda A/C's.
Common among all A/C’s.

Wife’s 2001 Pontiac Montana lost it’s A/C, she took it to the dealership and got a quote for $1700! (This was 2004) New compressor, condenser and lines. She was told the system was leaking and it all needed to be replaced.

I was in college taking the Refrigeration / HVAC courses at that time, figured I’d look at it. I saw no evidence of all that leakage. Nice coat of dry dust over everything.

Called my neighbor over, he’s a professional A/C mechanic for a trucking company. He said the same… so we put a can of refrigerant in it.

A/C worked fine. And when I disconnected the low side hose for the pressure gauge, oil was bubbling at the Schrader valve. Took a valve wrench and put about an eighth of a turn on it, bubbling stopped and it held refrigerant for years afterwards.

Love that dealership’s parts dept., the service dept. not so much. 💩
 

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Discussion Starter · #13 ·
Common among all A/C’s.

Wife’s 2001 Pontiac Montana lost it’s A/C, she took it to the dealership and got a quote for $1700! (This was 2004) New compressor, condenser and lines. She was told the system was leaking and it all needed to be replaced.

I was in college taking the Refrigeration / HVAC courses at that time, figured I’d look at it. I saw no evidence of all that leakage. Nice coat of dry dust over everything.

Called my neighbor over, he’s a professional A/C mechanic for a trucking company. He said the same… so we put a can of refrigerant in it.

A/C worked fine. And when I disconnected the low side hose for the pressure gauge, oil was bubbling at the Schrader valve. Took a valve wrench and put about an eighth of a turn on it, bubbling stopped and it held refrigerant for years afterwards.

Love that dealership’s parts dept., the service dept. not so much. 💩
Mine's the same on the low port valve. First time I saw it, just barely wet with the cap off, minimal bubbling. First time I hook up borrowed manifold gauges from parts store to check pressures, had a hard time getting low port to snap on. Turns out the last guy that borrowed the manifold set had failed to completely release the low-side valve depressor and my repeated attempts to quick-snap it further damaged the low-side Schrader valve. I too took a valve wrench to tighten it too no avail. Throughout the process, as I diagnosed pressures and removed the low-side cap, it would blow off in my hand and send the O-ring flying, which I had to sometimes search for, lol. Bottom line, plastic cap is still holding the pressure and A/C is working like a champ. Thank goodness the high side did not experience the same situation, as that could take out an eye.

CAUTION: Before using A/C manifold gauges, whether borrowed or otherwise, be sure that both high and low port valve connectors on the manifold gauge set have been fully retracted (counterclockwise) before beginning your work. Additionally, once they are hooked up, don't screw them down completely, only just enough until the gauges read pressure. If you tighten them further, you will certainly incur damage to your Schrader valves.
 
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