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Discussion Starter #1
My air conditioning blows fine in both the front and the rear, i.e., the blowers are working properly. However, the air in the front is cold (like it always has been), but the air in the rear is warm (not hot).

What is the first thing I should check? What is the second thing I should check? Any other advice and/or tips?

Thank for your help.
 

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When was the last time it was serviced, i.e. refrigerant pulled out, vacuumed down, and recharged?
 

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Discussion Starter #3
Never. This is the first time the AC has not worked properly.
 

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Probably a little low on refrigerant. Stick a meat thermometer in the front vent and blast the ac. Check your reading after having it running for a while. Reading when moving and on a stop and go traffic - Or just idling for a while. If its a 10+ deg difference. You are low. Mine blows 42 degree at idle. 40 when moving. In our 100+ degree weather.
 

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Discussion Starter #5
The outside air was 90-degrees.

The FRONT is as cold as it's always been. It's plenty cold. No problems in the front.

The REAR is warm. It's not as hot as the outside air, but it's still plenty warm.

If the system is low on refrigerant, wouldn't the front and the rear BOTH be the same temperature?
 

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Not necessarily. If it hasn't been serviced in the last 5-7 years the first thing I'd do is have that done. Even a properly sealed up system will lose an ounce per year so if that vehicle hasn't EVER been serviced then it could be 14 ounces low on refrigerant, or more. If it holds 28 ounces that means it's up to 50% low.

It needs to have what's left recovered, vacuumed down, and then have the proper amount put back in. Once they do that then it can be evaluated for proper operation, system pressures, etc. When they recover it they can tell you how much they recovered and tell you how low it was. That's where I'd start.
 

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I am not sure if there is a blend door at the rear. I know the coolant goes straight to the rear without any control from the front heater valve. Maybe the evaporator heater motor? HONDA OEM 99-04 Odyssey 3.5L-V6 Evaporator Heater-Motor 79350-S0X-A51 | eBay If that is controlling whether you have heat or cold air, then the motor may have failed and stuck midway to heat. Hence no cold air. Try just blowing the heater in rear and see what happens.
 

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A blend door back there is certainly a very good possibility. However, if the system has never been serviced then it's definitely low. Often times when refrigerant starts to get low the system will get colder before it gets warmer. That's because the system starts to freeze up. Then as it continues to get lower it will start to get warmer. On dual systems it can be a little more complicated on refrigerant flow, too. Additionally, low refrigerant means low oil to the compressor since the refrigerant carries the oil (think two-stroke engine on a weed eater or chain saw) to keep it lubricated. Most compressor failures are due to low oil which is caused by low refrigerant. Low refrigerant can also cause the symptoms described, just like a blend door can, so that's where I'd start. Start with a good working AC system and then track down any other electrical or mechanical issues that might also be there. That's the route I'd go if it were mine.
 

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+1 on getting it recharged before doing anything else. Also, +1 on the point that low charge reduces lube to the compressor. If that compressor goes out due to lack of lubrication, a $100 problem quickly turns into a $1500 problem.
 

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Discussion Starter #10
Do these vans have 1 or 2 evaporator coils? I.e., where is the rear air cooled? Is the rear air cooled by the evaporator coil located under the passenger-side dashboard? Or, is the rear air cooled by an evaporator coli located somewhere in the back of the van?
 

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Do these vans have 1 or 2 evaporator coils? I.e., where is the rear air cooled? Is the rear air cooled by the evaporator coil located under the passenger-side dashboard? Or, is the rear air cooled by an evaporator coli located somewhere in the back of the van?
There is a rear evap coil. There would almost have to be a blend door or you wouldn't have any temp control to the rear unit, only fan speed control. Personally I would lean toward a rear blend door issue IF the rear is blowing HOT as if it is blowing air through a hot rear heater core, but by your description that is not the case. I too would start by getting the system properly charged and see where that takes you.
 

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Discussion Starter #12
I suspect the rear expansion valve. It might be clogged.

I also suspect the rear heater & cooler motor assembly (the blend door motor).

I will investigate both.
 

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Stick to KISS! Get the system charged to a known capacity to avoid going down rabbit trails! Low charge is the most common issue with A/C systems, and can present itself as poor cooling in either front or rear individually.

Of course, if you put an a/c manifold gauge set on and measured high/low pressures and vent temperature at a given ambient temp, you'd have a lot more legitimate diagnostic information. Low pressure on both low and high sides would give further evidence of a low charge. Your theory of clogged expansion valve would present itself as high pressure on the low side with normal pressures on the high side. Such diagnostics is most deterministic with a known good charge level though. Marginal charge level, air in the system, etc, can confuse the diagnostics.
 

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Discussion Starter #14
Hello webbch,

Excellent advice! Great information. Many thanks!
 

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Discussion Starter #15
If I find a manifold gauge set that I can use, how do I know which Schrader valve is the high pressure and which Schrader valve is the low pressure?
 

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If I find a manifold gauge set that I can use, how do I know which Schrader valve is the high pressure and which Schrader valve is the low pressure?
High pressure will be color coded RED. Low pressure = BLUE. Also, on R-134a setups, the connectors are physically different sizes so you cannot hook them up to the wrong port by mistake. And there will be a YELLOW hose in the middle of the manifold gauge set for attaching the can of new refrigerant you'll be adding.

Also, the high pressure pipe will be smaller diameter than the low pressure, and if your AC works at all, the high pressure pipe will be hot to the touch, while the low pressure will be cold (and maybe insulated).

Schrader valve - yes, these will have Schrader valves, just like on your car or bike tires. Except different materials to be chemically compatible. But it is only the Schrader **core** that is similar between the two. So don't go looking for something like what you've got on your tires. The core/pin thing in the center will be the same, but the part surrounding it will be different.

And the Schrader valves are a fairly common failure point that will leak. They're also pretty easy to test /adjust. You can get a valve tool for about $2 at a bike store, auto store, or kmart, etc., which will allow you to unscrew / tighten / etc. the valve core. I'd get one of those, and practice on a bike tire to see how the core unscrews. You won't want to remove the core on the AC (although there are special tools to allow this without losing refrigerant), but you can maybe loosen it just a hair and reseat it, noticing how loose it was. Also, some tests on re-seating the spring-loaded valve may help - e.g., pull it tight with small pliers to make sure it is seated. You can put your finger over the valve to see if pressure builds up before / after any of this - to see if the valve itself was / is leaking.

I have a Snap On Halogen detector (fan-powered sniffer) which is amazing at detecting AC leaks in real time, non-invasively. I've seen China-brand ones on eBay for reasonable prices. May be a good investment.
 

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EDIT (10-minute limit blocked me) - after re-reading your original post, the stuff I said about leak-checking the Schrader valves is only relevant if your problem ends up being low refrigerant, and you need to find a leak. Unless you already have a leak, you might not want to go looking for one, since you might create one.
 

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Discussion Starter #18
Car OFF: Left gauge 94 PSI; right gauge 80 PSI.
Car at IDLE + AC on HIGH: Left gauge 150 PSI; right gauge 20.
Car at IDLE + AC OFF: Left gauge 57 PSI; right gauge 60 PSI.

Black and greasy around high-side Schrader valve. When the gauge set was removed, the high-side Schrader valve was bubbling. Diagnosis = the high-side Schrader valve is leaking.

If I can tighten the Schrader valve so it no longer leaks, what pressures do I need to achieve when I add some oil and refrigerant?
 

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Wait a while after AC gauge removal and spray soapy water on the ports and see if its still bubbling.

I used this tool to change the shrader valve on my low port. https://www.amazon.com/dp/B0015KH93K?tag=vs-auto-convert-amazon-20 I got the valve core from AZ a $10-kit. After the repair, I added plain 134a refrigerant ( got a case from sams club) Depending on ambient temp, you should be somewhere around 30-35 psi on low side. You only charge on the low side. While still watching your high side. You don't want that to go way over either. No more than 300 psi?(need to look in my notes) You also want to know the temp on the vents. So put a thermometer there. BTW, you want to get the ac reading while its running for a while. You will notice that after 15-20 mins or so, it will change. Specially after adding a small can of 134a. It will go up and then settle down. Good luck.
 

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Car OFF: Left gauge 94 PSI; right gauge 80 PSI.
Car at IDLE + AC on HIGH: Left gauge 150 PSI; right gauge 20.
Car at IDLE + AC OFF: Left gauge 57 PSI; right gauge 60 PSI.

Black and greasy around high-side Schrader valve. When the gauge set was removed, the high-side Schrader valve was bubbling. Diagnosis = the high-side Schrader valve is leaking.

If I can tighten the Schrader valve so it no longer leaks, what pressures do I need to achieve when I add some oil and refrigerant?
Was the "Car OFF" reading taken last, after the engine had been running during other tests? That would explain why the pressure had not equalized - takes some time. Also, when the compressor is not running, whether the engine is on or off, the pressure readings will increase with increasing ambient temperature (the temperature in the engine compartment where the AC tubes, etc. are.

That MasterCool kit nitely2 referred to is good. I have the extended version of their kit, which I've used, I think on my '99. But before getting a kit like that, etc., I'd first see if you can tighten / re-seat / adjust the leaking valve as I mentioned in a previous post. Also, you may as well do that before adding Freon.

The numbers you list are a little low. Here are the pages from the manual (for 1999). Be sure to follow the exact specs of how to run the test before you worry about the numbers. E.g., 1500 RPM. Hmm, how to do that without passengers in vehicle ... well you might need to bend the rules a little.


h99 AC pressure test_Page_1.jpg
h99 AC pressure test_Page_2.jpg
 
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