2002 Honda Odyssey Air Conditioning

Was messing with a 2002 Odyssey a few weeks ago, I ended up ultimately not being to duplicate the issue, but the client keeps coming back for the same issue. It's been in the parking lot untouched for a few weeks, so I'm unsure of what is going on with it now, but my shop foreman ended up taking the car over.

First time they came in for the issue, they were complaining of a "grinding noise" and smoke coming from under the hood accompanied with stalling. Test drove, couldn't verify any issues. Scanned for codes, no codes anywhere in the vehicle. Ended up letting the car run for a little bit, and found the pressure relief valve on the compressor randomly going off spewing R134 and making their "grinding" noise. Hooked up gauges and found low pressure on both high and low side. Evacuated system and got about half of system capacity. Recharged system to full capacity, and idled vehicle again. Checked fans for operation, fans okay. It spewed off through the relief valve once more, but still no issue found. Compressor cycling okay. Checked for restrictions in lines/components using laser temperature gun. No abnormalities found. Test drove vehicle again twice over the course of several hours, vehicle drove fine, no stalling, no venting, A/C blowing cold etc. Let vehicle go.

Came back two weeks later, same complaint. Again drove the vehicle, no issues. Hooked up gauges and watched pressures. Low side pressure went up to about 60, high side pressure was intermittently going up to 500psi, but compressor was still cycling and fans started turning on intermittently, but still no venting, and as soon as they turned on, pressure went down to about 175 on the high side, 40 on the low side. Swapped fan relay, no change. Test drove three times over the course of 5 hours, idling most of the time, with a short break in the middle. Could not duplicate client concern. Let vehicle go.

Van came back again about two days later, and at this point, shop foreman took vehicle back over.

Was just going to see if I maybe missed something whilst checking the system? Or maybe there's a better way to do things? Having a hard time actually getting trained at the shop, been relying on SD for a LOT.

Well high side pressure should never go that high. My hunch is the stv valve is intermittently sticking closed. It looked like a block of aluminum that the lines bolt to on the firewall going to the evaporator core. When that sticks closed the high side pressure builds up and the low side drops to zero or even a vacuum.

Hardtopdr2 wrote: My hunch is the stv valve is intermittently sticking closed.

Do you mean TXV (Thermal eXpansion Valve)?

In addition, I would keep a close eye on the fan operation. Do a wiggle test on the wiring harness. Look at current waveform, if you can. As well as air flow through the condenser. Make sure the condenser isn't clogged with bugs, grass, dirt, etc.

Yes that's what I meant autocorrect is begining to tick me off

Right, I would expect to see the high side go between 150-200ish (depending on ambient temp), so when I saw it get passed 300, and all the way up to 500, I was very confused as to why the compressor wasn’t shutting off. And see I was thinking TXV, but I had no way to verify this theory. Is there a quick check that can be done? Wiggle test and current waveform on the fans were done as someone else on here suggested, and everything was normal.

Actually you did have verification... 500 psi of verification. Go on Amazon and order the mastercool automotive a/c basic service manual. This is a good book to have to learn diagnostic of a/c systems. Also I would say if vehicle has a high pressure switch it definitely needs looked at cause it should have dissabled a/c going that high

I could use a copy of that myself, thanks!

I'd be looking at the fans first since everything appears to be working normally when they're on. It kinda sounds like they're missing AC control and just cycling on and off with ECT. Take a look in SI to see what the fans are supposed to be doing with AC on. And while you're in there see if the vehicle has a high side cut-off switch.

Understanding a couple basic fundamentals makes diagnosing A/C systems much easier.

First of all, pressure changes the boiling/dew point of liquids. Under pressure, the boiling point is higher.

Second, you can not "put cold into" anything. But, you can remove/transfer heat. When a liquid changes from liquid, to a gas, it absorbs heat. When a gas changes to a liquid, it disperses its heat. In short, "the cold happens" when the refrigerant changes from a liquid to a gas.

Now, let's look at the refrigeration cycle. If we start at the COMPRESSOR, the compressor "sucks" in a LOW-pressure gas, and compresses it into a HIGH-pressure gas. This HIGH-pressure line gets hot, as you probably know. The next component in the "loop" is the CONDENSER. The Condenser is the "radiator-looking thing", in the grille. Here, the HOT HIGH-pressure gas is cooled, and condenses into a HIGH-pressure liquid. (Remember what happens when a gas changes to a liquid?) The next component is the TXV, or ORIFICE TUBE (one, or the other). This is where the pressure drops. Due to the drop in pressure, the now LOW-pressure liquid can boil, and turn into a LOW-pressure gas. (Remember what happens when a liquid changes to a gas?) This happens in the EVAPORATOR, which lives under the dash. Now, the LOW-pressure gas goes through the (Accumulator/Receiver/Drier), on its way to the compressor, where the cycle repeats.

The two points of heat exchange are the Evaporator Core, and the Condenser. If either on has a problem exchanging heat, Pressures will be affected.

Any place there is a restriction (pressure drop), there will be a temperature change.

Make sure the fans are turning the correct way should feel air flow with your hand in front of them. I had a 2013 Camaro 1 was spinning backward ms the high side pressure was way high. Reversed wires in connector all fixed