A/C not working in front, but rear blows cold (heater valve issue)

[bigeo]

A couple of years ago I got a recommendation from a friend for a good repair shop that is close to where I live. I have had them do a few repairs on my vans and they have also worked on my son's Camry. I have been happy with their work and what they charge. A bonus for me is that the owner has a genuine appreciation for Toyota vans. I developed enough faith in them that I took my 87 4WD in at the beginning of last summer to see if they could resurrect the AC. They put in a rebuilt compressor, recharged the system and I had working AC for far less $ than I expected.
When the weather finally warmed up here recently in the PNW, I switched on the front AC and got warm, not cold, air out of the vents. I took the van back to the shop and was told that the rebuilt compressor (from O'Reillys) was no longer doing the job. I haven't had much luck with rebuilt stuff from the auto parts stores in recent years, so I wasn't too surprised. I offered to get a "new" rebuilt for them to put in and purchased a Denso from Rock Auto. While I was awaiting its arrival I switched on the rear AC while driving and found that I was getting cold air out the back. That made me question their diagnosis but the new compressor was already on the way. I had them install it when it arrived and the front AC still didn't blow cold. The current explanation for the problem is a stuck heater valve. The owner of the shop didn't charge me for the work they did and said he would install a heater valve for free if I could find one.
My questions are: Is a stuck heater valve a good explanation for the symptoms? Since heater valves don't seem to be available for these vans, what are my options for getting my front AC to work. Could I bypass the valve so I can have AC (but, presumably, no heat) for the warm part of the year? Has anyone been able to find a heater valve for another vehicle that they were able to make work on their van?

[trestlehed]

Did your shop actually check with Toyota to see if that part is still available?

If that part is NLA for the van, you might want to pull that heater valve, take it to Toyota parts and see if it matches the one used on
Toyota trucks of similar year/s of manufacture.
Otherwise you should hit the junkyards.

[bigeo]

There are actually two 89 vans in a Pick n Pull north of Seattle and I pulled the heater valves (and a few other parts) off both of them today. They don't look quite the same as the one on my van (no bent metal piping) but my mechanic says he can make it work. Should know soon if that fixes the AC issue.

[bigeo]

Quick update: I swapped out the heater valve myself since the shop was booked for a week. AC now blowing cold. FYI the plastic heater valve I pulled from the 89 was a direct replacement for the metal one from my 87 even though it looks quite different. Let the hot weather come

[ncbrock]

I tried to get my AC working today after installing a ton of new o-rings, a new compressor, and new drier. The van passes the vacuum leak down test, all the functions of the AC system work. All the buttons work, fans work, idle-up and everything works the way it should. The rear blows pretty cold, and the refrigerator seems like it can make ice, but the front is just ambient air temperature no matter how I aim the air or mess with the fans. Looking for some ideas on what to check or replace.

[Burntboot]

I would be looking to the front expansion valve, as the culprit.

[ncbrock]

Ok it’s getting absolutely brutal outside and still haven’t fixed this issue. Replaced the front expansion valve, cleaned out the evaporator (externally) and isnt clogged internally. I fixed the seal on my hvac blend door and the cables are operating properly as the blend door seals off the heater core when you turn the knob to the blue side. I can’t really tell if the front evaporator is even getting cold because it’s kind of sealed up under the dash. The low pressure line from the front evaporator that is shared with the refrigerator gets icy if that means anything

[Burntboot]

Beyond my depth but did a little looking about and found this, while its referencing residential, same principles apply


It's all about the temperature/pressure relationship, and how pressure affects the boiling point of the refrigerant. As the pressure of a refrigerant goes up, so too does the temperature and boiling point. When the pressure drops, the temperature and boiling point drop as well. Air conditioning (and some heating) systems take advantage of this, to cool (heat) the air inside a building.
Normal systemIn a normal system, The compressor compresses the refrigerant vapor. This causes the vapor to be both high temperature, and high pressure. The hot vapor moves through the condenser coils, where some of the heat is transferred into the outside air. When the vapor finally comes out of the condenser, it's a hot liquid. The hot liquid moves through the liquid line, into the building towards the evaporator coils. Just before the hot liquid refrigerant reaches the evaporator, it's forced through a metering device. The actual device used depends on the system, but capillary tubes are common.
When the hot liquid is forced through the metering device, the pressure drops substantially. The pressure drop causes the temperature and boiling point of the liquid to also drop. As indoor air is forced over the evaporator coils, the cold liquid refrigerant in the coils absorbs heat from the air. The heat causes the refrigerant to boil, which changes it to a low pressure vapor. When the refrigerant reaches the end of the evaporator, it's a cool vapor. The cool vapor travels down the suction line, and back to the compressor where the refrigeration cycle can start again.
Low refrigerantWhen the refrigerant in the system is low, the pressure; and therefore temperature, of the refrigerant will also be lower. In a normal system, the temperature of the refrigerant at the beginning of the evaporator will be right around the freezing temperature of water (32°F). As the indoor air moves over the cool coils, the moisture in the air will condense on the coils. This condensation will drip harmlessly off the coils, and into the condensate drain.
When the refrigerant is low, the temperature of the refrigerant at the beginning of the evaporator coils will be colder than the freezing point of water (less than 32°F). Because the coils are so cold, the condensation that forms on the coils will freeze. As ice builds up on the coils, it restricts the air flow through the coils. Because of the restriction, the refrigerant can't absorb as much heat from the the indoor air moving over the coils. This causes the refrigerant to boil later in the evaporator, which causes ice to form further along the coils. This situation continues to progress, until the whole evaporator is a block of ice. Once that happens, the refrigerant will start to boil in the suction line. This cause the temperature of the suction line to drop, and just like in the evaporator, cause the condensation to freeze.
Eventually the freezing works its way all the way back to the compressor, which is where the trouble can really start. If allowed to operate in this condition for too long, liquid refrigerant can make its way back to the compressor. If this happens, the compressor can be damaged.
It should also be noted. Once the refrigerant level drops too low, the system stops working. So this problem only occurs in a "sweet spot", where the refrigerant is low, but not too low.

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Not sure, but sounds like you might just be low on freon?

[Burntboot]

And from the RedTek site:













Abnormal Pressure Gauge Readings




Low Pressure Gauge is High and High Pressure Gauge is High
Condition normally indicates an overcharged system. Slowly remove refrigerant through low side service port until gauge readings are normal or until proper cooling returns.

Low Pressure Gauge is High and High Pressure Gauge is Low

Condition normally indicates faulty reed valves in compressor when this condition is accompanied by extremely vibrating gauge needle. Compressor service is required.

Low Pressure Gauge is Low and High Pressure Gauge is Low

Condition normally indicates low refrigerant charge. Add refrigerant until gauge readings are normal or proper cooling returns.

Low Pressure Gauge is Low and High Pressure Gauge is High

Condition normally indicates blockage in air condition system. Service is required.

[ncbrock]

It was the magnetic valve wiring. AC is working perfectly now, about to switch it over to RedTek from R134a

[Burntboot]

Sweet!
Wait, I should say "COOL"

:dance2:

[MyToy]

Can you describe where this valve is? I just did all by AC over and finally stopped all the leaks. Hey BB, it was the compressor after all.
But it get cool but not real cold. The rear is a tad better.
Maybe I should check this magnetic valve.

It would be a big help if you can tell me where it is located.

MT

[ncbrock]

On my 4WD van is is above the condenser (you have to lower it) and it is a cylindrical valve mounted on the drivers side “frame” rail. Shiny metal vavle that says “Nipondenso” on it.

[MyToy]

Thank you for your input. I think the 4wdr unit is different. I did find a cylindrical type of something with 2 wires on it in front of the front condenser connected between 2 somewhat thin tubes. I will try to take a pic of it and see if it says anything like Nipon on it.

It is a real bummer though. The are puts out, at it best, about 80deg if I put a thermometer in the throat of the front middle AC vent. The compressor is still working and the rear, after measuring, really isn't much better then the front. It is basically a waste of time on the extra fuel to run it. It does nothing.

Maybe by some miracle its the valves.

Thanks again for the feedback.

MT

[devin.mendez@icloud.com]

I’m currently dealing with the same issue. How much was it? And where did you get it? Did you have to drain the system to install?

[David C]

Currently have this problem and I am ready and willing to tackle it. Does anyone know the part number for the AC Expansion Valve on a YR30 from 1992?

***UPDATE: I actually found it by using the BEFORWARD site, a JDM parts site in Japan: part number
8851587002.