Diagnosing expansion valve stuck open vs faulty compressor?

[brian0918]

I'm having an ongoing issue with the A/C on my 2006 Honda Accord.

With outside temperature around 85-90, the passenger vent is only getting down to 65, and the driver vent is closer to ambient temperature, 75-85. Thinking the vent temp difference was due to the driver's blend door actuator, I took it out and shut the blend door all the way, but the driver's side still blows warm. I also checked the heater control valve, and it is properly opening/closing when the actuator pulls the cable.

Honda says the vent temperature difference could be due to low refrigerant, because it enters the evaporator on the passenger's side, and only cools that side.

My gauges showed about 100-110 High side, 30-40 Low side. And when I turn the A/C off, the pressures hold, and equalize slowly.

Also, the car's diagnostic mode shows the Evaporator Outlet Temperature is higher than normal - about 60-65.

I took it to a shop that checked for leaks (UV dye was already in the system) and found none. They believed it was overcharged (by me) and evacuated and recharged. It made no difference in vent temp, and the gauges showed the same readings as before. High side is about 100, Low side is about 40.

So it seems like the refrigerant is evaporating completely before it reaches the driver's side of the evaporator - due to the lack of sufficient pressure differential between High and Low sides.

The compressor seems to be running constantly. The A/C line after the compressor gets very hot, about 165F. The condenser seems to be working alright, as it drops the temperature of the line to about 115F.

I am starting to believe there is a problem with either the expansion valve stuck open, or a faulty compressor.

Any suggestions for diagnosing this problem further? Thanks!

[Cusser]

Did you add 19 oz. refrigerant? That's what I see online. Because 110 psi on high side is real low. Didn't the "shop" that added refrigerant and checked for leaks realize that 110 psi was way too low and investigate ????

[brian0918]

I tried adding more refrigerant initially, but then apparently I overcharged it, because the safety valve on the compressor started spraying out refrigerant and oil.

The shop is very highly reviewed and one of the most popular in the county. I know that doesn't necessarily mean they can diagnose A/C problems.

They said they evacuated and recharged with the correct amount of refrigerant and oil. I don't know why they didn't notice the pressure problem on the gauges afterward. I asked the guy what the gauge readings were, but he said the mechanic didn't write them down. I'll be getting back with them on that.

If it's just low on refrigerant, why is the Low side normal? Shouldn't it be low as well?

[bohica2xo]

Put your gauges on it.

Full load test

Doors open, cabin fan on highest speed. Run the engine RPM @ 2000 for one minute to stabilize, and record pressures while at 2000 engine RPM.

Post the readings.

[mk378]

Pressure equalizing slowly at shutdown means that the expansion valve is closing like it should in that case. If it were stuck open, the pressures would equalize rapidly.

[brian0918]

Sorry for the delay. That shop wanted to check again for any leaks. They said they couldn't find any leaks, and that their recovery/recharge machine didn't find any problems with the system, so they think it's a blend door problem. I tried to ask them what the pressures were, and they said you can't use manifold gauges reliably to confirm it's working properly, and their machine was $5000 so you can trust it more.

Here are the test results with 82F ambient temperature, doors open, vents blowing high on max cool:

After running at idle for a while: 80 High, 22 Low.

After running at 2000 rpm for a minute: 90 High, 14 Low.

Then going back to idle: 105 High, 30 Low.

Then disabling A/C: High side increased to 200, Low side increased to 55.

I also checked the diagnostic mode values, because the vent was blowing colder than it usually does:

1. In-car temp: 84F
2. Ambient temp: 82F
3. Sunlight sensor: 01 (very dark)
4. Coolant temp: 198F
5. Evaporator outlet temp: 64F (still high?)
6. Driver's air mix opening: 32%
7. Passenger air mix opening: 01%
8. Vehicle speed: 0
9. Vent Temperature Air Out (TAO): C0 (conversion chart says: -4 F which I don't understand)

[bohica2xo]

That compressor is worn out.

I guess the 5k machine missed that part.

[mk378]

...If the machine and operator can be trusted to put in the right amount of refrigerant. Ordinarily, seeing pressures like 90 / 15 the first thought would be "badly undercharged."

Seems really weird that the high side goes up when cut off. I wonder if anything was measured properly.

You may have a bad TAO sensor, I don't know how that would affect the rest of the system. It looks like the 4 cylinder anyway uses a conventional constant displacement compressor with "bang-bang" control via the clutch.

[brian0918]

That compressor is worn out.

I guess the 5k machine missed that part.

Just so I can understand, what's leading you to that conclusion? And why does the high side pressure go up when the A/C is turned off?

Should I take it to a dealer at this point for confirmation? Or just find another shop to try replacing the compressor?

[bohica2xo]

A 10 psi shift in pressures at 2,000 engine rpm means the pump is not moving much volume.

If the system was under charged, I would expect to see the low side drop quite a bit - even into vacuum if not equipped with a LPCO.

You can add a few ounces of refrigerant and re-test if you are still unsure.

The pressures went up after shutdown from heat soak. Just static pressure change with temperature.