QuestionI need some help diagnosing a problem that I'm having with my 2001 Ford Expedition (150,000 miles) The other day, I noticed that the rear A/C was blowing hot air while the front was blowing cold. I checked the charge and according to the gauge that I bought it was on the high-end of the appropriate psi range. I'm sorry, I forgot what that number was but I want to say 65 psi.
At any rate, I believe I ruled out any freon leaking for the time being, so I pulled the trim off of the back of the SUV and found the rear A/C unit. I inspected both door actuators and they were working great, so I took out the blend door and noticed that the foam covering had partially melted off of the door itself, causing the door to not be able to fully open or shut. So I super-glued that back on, inspected the rest of the door, and put everything back together. I thought for sure this would fix the problem, but unfortunately it only made it marginally better. Now it blows cold A/C when the ambient temperature is less than roughly 85 degrees, but I live in Texas where it's almost 90 degrees by the time I get to work in the morning this time of year.
I had somebody in the dealership mention the expansion valve - Is there a separate one in the back? I've also had another novice (besides myself) tell me that there's a valve that directs freon from the front to the rear, but that doesn't seem likely to me.
In short: HELP!!!
AnswerWill,
The dealership is correct. There is a metering device for the rear evaporator. Every evaporator needs a separate metering device all to itself. Would I jump straight to saying this is the fault? Absolutely not. But it is a possibility. I understand that you checked the pressure and it read 65 on that gauge you bought. And I do not mean to sound condescending at all, but those little gauges you buy at autozon, or wherever designed to be used with the little recharge canisters really are not that useful or reliable. If you have access to a set of A/C gauges, take the pressures again. Sen dme your high side and low side readings as well as the temperature outside when you take them. As you take them the truck should be at roughly 1300-1800 RPM, as this is the range that automotive compressors are designed to work at. If you do a followup and send me this information I can definitively rule out a low charge, but as always, if it is not blowing as cool as it should, that is the first fault to come to mind. If it is correctly charged as you say, then my next stop would be to the metering device. In the rear, the expedition does have an expansion valve that adjusts for the heat load that is being placed on the evaporator. Easiest way to check this is to take the sensing bulb off the outlet of the evaporator. Heat it up, Not with a flame, just grip it in your hand. The heat from your hand should be more than enough to make it open more. As You heat up the bulb, there will be a difference in temperature if you touch the evaporator inlet line, (or even the evaporator itself) It will get colder as the expansion valve allows more refrigerant to flow through it. Or if you have your gauges hooked up, the low side pressure will change rather dramatically. But with you in the rear, and the gauges in front, that would be hard to do. On most automotive systems, inside the inlet to the metering device there is a small screen to basically filter out any particulate matter that may be flowing through the line. This screen may have gotten clogged or blocked. Or the metering device diaghram may have just given out and is no longer opening more when you have a high heat load.
You are correct, there is no other valve directing refrigerant to the rear unit. I believe the other novice was thinking of something along the lines of a solenoid valve, and no vehicle I have ever experienced, other than RV-type units have such a valve.
In short(as you put it)- First stop, check or have checked your refrigerant charge with a set of real gauges, before you go to changing parts. If your charge is dead on, AND, your blend door is completely opening and closing, then I agree with the dealer and your rear expansion valve is probably the culprit. For an expedition, the part (not bought from the dealer) should run about 45-50 dollars. But the labor may end up getting you. The refrigerant will need to be recovered, the system pulled into a vaccuum, and charged back up. As well as replacing the valve itself.
I hope I was of a little help, thank you for the question.
