Guys,
I'd like to get some opinions on this:
Is it possible for a TXV (expansion valve) to stick closed on an intermittent basis?

Vehicle: 2005 Odyssey Touring (w/ rear A/C)
System has worked normally for years. I did have to replace a clutch relay that caused some issues several months ago.

Symptoms: Occasionally, when starting the car with the A/C on, it will turn on and you can hear the clutch engage then immediately turn off. It appears that the high pressure switch kicks the systems off. Most of the time if you turn the off and then re-start it will begin cooling properly.
When it fails, I can override the clutch relay and force the compressor on, then high side pressure rises to ~500psi. The low side pressure seems to go to 50psi. Obviously, I did not leave it there for long. When the car is off, pressure equalizes to ~130psi. It doesn't seem to be leaking because when the A/C works, it works great. And once it starts it seems to continue to work.....even on a 2 hour trip. The compressor can be turned by hand with little effort. You can see the clutch engaging properly with no slip.

I'd like to get an accurate diagnosis before evacuating the system.

Thanks in advance!

 

yes, its possible but it sounds like you might be overcharged with 130psi static presure with the ac off

 

Ditto the above, ^^^ I would have the A/C refrigerant charge checked, [quantity] but because it is intermittent my guess is it is an expansion valve problem.

Have you tested it with the rear A/C off and just the front A/C on?

If no difference, I would replace both expansion valves and then properly recharge system, [at least 1hr on a vac. pump] with correct amount of refrigerant.94

 

Thanks for the advice.
@fcm, Yes. I tried to operate the front only. The front fan, etc. shuts off almost immediately. The rear fan will still operate but no cooling because the compressor isn't running. This gets into an area where I have little understanding. If I were to only run rear A/C, is there any refrigerant running through the front expansion valve? In other words, are both expansion valves in parallel? If so, both would have to be stuck closed in my situation?

Thank you.

 

Wait /what, you say the FAN shuts off almost immediately, are you now saying it is the blower fan that turns off????

If so then the problem is the fan circuit, the A/C system, including rear will not work if the front blower fan is not on, the ground trigger control for the A/C system, [A/C request] comes from the front blower fan speed control. 94

 

Yes. The whole "system" shuts down.... because of the high pressure.....I believe. So, when you start the car with A/C On, you can see the lights turn on, fan turns on, the compressor kicks on, then after a second or two..... recirc and auto lights go off......compressor turns off, fan turns off. The fan works fine as long as you don't start the care with A/C on. I guess I could post a video if it helps.

The rear fan continues to work independently.

 

Before starting the car, disconnect the pressure switch connector and test for continuity. You should have continuity. If not, then you have either too much refrigerant or not enough. It's likely you have too much as I said. If you have continuity, you will need to pick up some manifold gauges and see what's going on with the pressure when you have someone start the car and the ac shuts down. Normally when an expansion valve is bad and is sticking closed, it will force the evap to freeze over, which the evap temp sensor shuts down the system after it gets below freezing as a safety precaution.

 

Ok. Thank you for the suggestion. I can test the switch. The service manual indicates that the High-Low Pressure switch stops the A/C request to the PCM >455psi and <28psi.

I have gauges, vacuum pump and all the tools I should need for the job. I'm just trying to make a proper diagnosis before tearing into it.

It seems unlikely to me that this problem is a result of being overcharged since the system has functioned properly for years prior to this. Everything I read indicates that when the expansion valves sticks closed the low side pressure will go very low. In my case, that doesn't seem to happen....at least not before the high side gets dangerously high.

After jumping the compressor relay to force the compressor to run the high side becomes ~500psi and the low side is ~50psi.

 

I checked the continuity of the high-low switch. It is on.

I also ran a self-diagnostic test and got C(open outside temp sensor circuit), and J(short in driver's air mix motor control circuit).
I ran a second self-diagnostic moments later and got C (open outside temp sensor circuit).

This doesn't seem related to the original problem.

 

Never run into a car where the blower fan would turn off when A/C turned off because of high side pressure.

With that said, 500PSI high side pressure is a sure sign the expansion valve is sticking, if it ever goes higher you will blow off a ferrule off at a fitting. 94

 

If it goes any higher the relief valve will crack open and let some refrigerant out.

 

There is no "relief valve" there has not been relief valves on A/C compressors for some time now, you can't even buy replacement relief vales anymore, they are replaced with a pressure switch that you run the clutch coil lead through here in Canada anyway, I can't see the EPA allowing it either. 94

 

A/C COMPRESSOR for 2005 Honda ODYSSEY

part 2 is the relief valve

 

My mistake, I looked at the replacement compressors and they do not have them.94

 

On the majority of vehcles(including Honda) 450 PSI is about the relief point

I know you corrected your self on the pressure valve,(yeah theyre still around,somewhat)but have you ever seen a ferrule blow off?

Just curious,I never have.

 

Yes.
AC pressure doesnt rise that quickly. What are the gauge readings when this occurs?
Are you sure about that? What type of gauges are you using?

Ambient temp and the above requested readings are needed to help,sounds like maybe an issue with the pressure switch.

 

Ok. Maybe immediately is a bit of an exaggeration. Let's call it 3 seconds.

I just went out to take a video. And it's functioning properly.
Ambient = 75F, High Side ~175psig, Low Side ~45psig.
This is what is so frustrating. It's intermittent. I'll try to get a video when the pressure is high.

I use Mastercool aluminum manifold automotive gauges.
Here's a pic of static pressure(~130psi) at about 95F ambient.


So, how are the two(front and rear) expansion valves "connected". Do they both "see" the same liquid line pressure?

Would they both have to be stuck closed to see very high pressures? Keep in mind that I am assuming since the issue is intermittent, that a liquid line obstruction is unlikely.

 

In the 10 + years I did A/C I have seen it more then a few times, it is the weak point the A/C hose is good to 800PSI and aluminum lines to well over that, the weak points are the connection points and the weakest connection point is the crimped ferrule with the non barbed ferrule being the weakest.


The gauges shows the low side is almost pined, was it connected?
The liquid line is the line the expansion valves are on and yes they are paralleled, [front and rear expansion valves both "see" the same liquid line pressure] 94

 

Yes. Both gauges are reading roughly the same pressure in the pic. The low side gauge maxs out at about 250.

I am at a loss.
I replaced the front expansion valve. Everything worked great for about a week......then it quit....again.

I began paying close attention to the outside/ambient temperature sensor after the HVAC self-diagnostic reported "open outside temp sensor circuit". While the HVAC is not functioning, the temp reading seems to be "inaccurate" i.e. at 73F while the actual temperature is closer to 83F. In that case, I replaced the sensor and it still read 73F. The wire harness looks fine where I can see it.

 

You should replace the rear too.

 

Ditto the above, replace the rear also.
Question, did you flush the system before recharging it?
One of the ways I have seen a expansion valve stick is the desiccant bag in the filter/dryer breaks open sending desiccant throughout the system, it needs to be flushed out, you can usually see evidence of that in the expansion valve and lines, looks like white sand.
If you do see that you must replace the filter/dryer also. 94