My front vents are not blowing cold, but the rear is freezing. First I thought maybe the evaporator core was plugged. I pulled the blower motor and it's clean as a whistle and the evaporator core is cold. So I pulled the cover behind the glove box and I see that the heater core is hot. I checked the blend door operation and it works fine although the thin piece of foam that was on it pealed off and was stuck and partially blocking some air flow, I got rid of that but it didn't seem to make a difference. I figured I don't have a vacuum leak because everything else works fine, the flow changes from defrost to main vents and lower vents with no issues or delay.

So my next guess was the heater control valve under the hood. I pulled the vacuum hose off of it and it seemed like there was vacuum there went I put my finger over the hose. I ordered a new valve. I figured let me test the operation of the new valve before I pull all the heater hoses apart. Nothing. I then put a vacuum hand pump tester on it (I should have done this before ordering a new part) and I got nothing. I tested the new valve and it works with the hand pump. So I used the hand pump to actuate the existing valve and it seems to be working and blowing cool air now. I started testing all the hoses back to the dash and they seem to hold a vacuum.

So my question is, what is the logic in the electronic automatic temperature control to actuate the heater control valve? Or is my eatc no good? There's also a separate vacuum control valve/module behind the eatc and I can't seem to find a part number for it anywhere online. I guess a diagram for the eatc system would help me a little bit I can't find that either. Anyone have any ideas?

Thanks

 

Per the '03 factory service manual, for example, it says "The automatic temper control solenoid and manifold will supply vacuum and close the heater control valve depending on the EATC module settings and ambient conditions in any setting except OFF"
Yeah, that's the remote solenoid/manifold module that holds all of the vacuum control solenoids and the vacuum connections.

BTW, if you want any technical drawings etc, you MUST identify the vehicle completely. There were changes over the years.

 

I found a thread on the 6.0l forum that has the diagrams and I came across that same note. It also says there should be vacuum at the valve when the eatc is "off". So I tried that and still nothing. I'm wondering if because it was night time, the logic of the system didn't sense anything from the sunload sensor and therefore didn't send the vacuum signal. I'll try again in the afternoon today. And if that doesn't work I may need to pull the dash and test the manifold.

And yes, I forgot to mention it was a 2002 limited v10.

 

Update:

I ran the self test on the eatc, it didn't come back with any codes. But after I ran the test I started getting vacuum again at the heater valve when I had it set to the coldest temperature, not sure if running the test reset something or the fact that it was warmer and sunny out had something to do with it. But the core was still warm so I swapped out the valve. I tested the old valve and it did seem to function but it would get stuck in the closed position. Could be it was getting stuck open when there was coolant flowing. Anyway, I still have an issue, the rear vents are blowing at 45 degrees and the front is about 69 or 70. I think the expansion valve is plugged. Weird because the evaporator coil was pretty cold. I'm going to put a thermometer on the evaporator coil and see what I get.

 

I did some more testing today. I found that the door to change between outside air and cabin air is broken and I can't find the part anywhere online. It's broken where it connects inside the cabin behind the heater core so instead of working properly it's just bouncing around. I held it closed manually and the temperature at the vent went down to 66 but that's still terrible compared to the 45 - 47 of the rear. The other thing I noticed is that the low pressure line coming off the evaporator core is warm. The high pressure line is freezing right after the orifice tube. For the rear A/C, the low pressure line is cold. I think something is partially blocking the flow of freon through the front evaporator, it's possible I need to service the orifice tube or maybe the evaporator itself is partially blocked. I stuck an inspection camera into the duct from behind the dash so I could check on the reverse side of the evaporator core and it was clean as a whistle in there.

 

First time I've heard of for that one to be broken.

\Usually a symptom of a low charge.

 

Just my luck. I did some more googling and found a diagram with a part number. It's F81Z-18K542-AA and only about $9. It's the lever that actuates the door, not the door itself.
I thought of that but then wouldn't the rear be warm too? It's blowing at 45 degrees at the rear vents, pretty cold in my book. Unless maybe because the orifice is partially clogged it has more resistance so whatever freon is left in the system is going to the rear? If that's the case then I should clean/replace the orifice anyway.

 

If you are frosting at the orifice entry point, low charge, and or clogged orifice screen are to be suspect.
The orifice up front by nature is it's own restriction therefore causing the to refrigerant meter and change into vapor. If the entry point of the orifice is blocked/restricted with debris, than this can cause a new point of metering.
What's needed is a set of gauges to look at both high and low side system pressures.

 

It's really hard for the evaporator to get clogged internally. The only way for that to happen is for the screen on the orifice tube to get torn or damaged.

Evacuation of the system and inspection/replacement of the orifice tube would be my first order of business. If the existing orifice tube is clean enough, I'd replace it anyway (they're cheap) and then recharge the system properly by weight.

 

Yes, my plan is to evacuate the system and replace the orifice tube. I found a kit on rockauto for $25 that includes the tune, o rings and a drier. I'm not sure how good the drier is in that kit, seems a little cheap to be of high quality so I might just do the orifice tube and recharge it.

 

I replaced the orifice tube and drier, the orifice was disgustingly dirty, it looked like it had wood chips in it. No idea how that could have gotten into the system. Problem is, I didn't bother replacing the rear expansion valve because the rear was cold before. Well that was a mistake and now the rear is warm. The front is freezing though!

 

I have my OE compressor sitting in a box after installing a new OE earlier this year, I plan to open it up and see if those orange bits are coming from the compressor, which I believe they are.

 

I really hope they aren't coming from the compressor. I'm not looking to spend any more money on it, the rockers are rusting out and for what it'll cost to fix I can buy a rust free truck or maybe something else. I mean, I like the Ex but I've spent a lot over the years keeping it running and I don't use it enough to justify putting that much money into it. I don't think I'm going to fix the rear A/C for now, I'm just going to leave it.

 

I have never seen that much debris in an orifice tube without the compressor making a ton of noise. If it was a diesel maybe you wouldn't hear it, but in a 6.8 that compressor should be noticeably noisy.

 

It makes a slight tick when it's running but no other noises. And it's done that since I got it 6 years ago. Oh and my 6.8 is quite noisy, rusted off manifold studs will do that, lol. I think it's the inside of the rubber hoses degrading and cracking.