2000 expedition. I started it up a couple days ago & heard a high pressure type of sound & smelled refrigerant. It lasted for about 5 seconds. The A/C still worked though.

Today the same thing, I was driving & I heard the same high pressure venting sound, opened the door & smelled refrigerant again. Once again the a/C is still working. I am guessing that there is a high pressure relief valve on the compressor??

This is my wifes truck & I don't drive it often, I am thinking that either the fan clutch isn't working enough causing the higher pressures in the A/C system or maybe it's overcharged. I put gauges on it & it seems to be OK. It's also 110 degrees here!

Any ideas??? Thanks.

 

There is a blow-off valve on the compressor that vents when pressure at the manifold gets extremely high, somewhere around 450 psi, IIRC.

If yours has been venting, it won't work much longer....

Yes, a weak fan clutch can cause this as can a high side restriction. The only way an overcharge could explain it is if someone added refrigerant and overfilled it, but you didn't indicate an such work.

Steve

 

Check the condenser to make sure there isn't debris restricting the flow of air .

 

I agree with both previous posts. Keep in mind that when the freon is forced out through the bow-off valve, its not only leaking freon...but also oil! If the a/c hasn't been worked on, I would look at the fan clutch or some kind of restriction on the condenser.

 

Thanks guys!

I did add about 10oz of refrigerant, however this was at the beginning of the summer & it needed it since the system was low. I used gauges, thermometer, etc. This was months ago & the A/C issue just recently started so I can rule out it being overcharged. I have charged several A/C systems & I have an A/C automotive certification. This doesn't mean that I know everything though, There is always more to learn I am sure. Just trying to make the point that I wouldn't overcharge it.

I need to pay attention to the fan clutch next time i drive it. I remember that it really used to pull air, You could hear it, very loud on a hot day. I will need to see if it's still the same. My wife doesn't pay attention to stuff like that! Just the stereo, LOL.

Thanks for the info guys! I will let you know what I find out.

 

I would drive the truck and get it good and warm, then check the fan clutch. Keep in mind that it doesn't matter what its doing going down(if you were driving 100% of the time, you wouldn't need a fan) the road, what matters is when its sitting still.

Are you sure it cools o.k.? If the fan winds up being o.k., I'd look for a problem or restriction allowing the high side pressure to jump.

 

I guess you are right about it going down the road. It gets plenty of air through the grille. Well, I warmed it up last night & spun the fan by hand. It didn't turn but half a turn or so if even that, so it seems like it's working. You can hear the fan clutch engage & dis-engage as the engine heats up & then cools down at an idle. I would think that this is normal since it's thermostaticly controlled.

Each time that it has vented through the relief valve it has been just after a hot start up. It may have been sitting for a hour or so max. I have noticed that the fan clutch doesn't seem to pull a lot of air upon start up. It starts working once you get down the road & the heat from the radiator hits the clutch.

I checked the condensor & it's free of any external blockage (airflow) When the gauges are hooked up, yes the high side is up there at first however once the system settles & the airflow starts pulling over the condensor then the pressures are within normal range. I am really thinking that this is due to a lack of airflow upon start up & shortly after. Could the fan clutch just be slow to engage or lazy? Or would it be all or nothing? I really don't wanna replace it if it's good. I have never liked fan clutches, I would prefer a flex fan or an electric fan, but it's what it has so it must be able to get the job done.


One last thing, The A/C does cool but I have never thought it was anything to be excited about untill you are on the highway. In town it works just OK. I understand that it's a large area to cool & the rear air drawing off of the same compressor has to be hard on it & not terribly effiecient. Plus it's 110+ degrees in the shade here in Vegas!


Thanks, Rich

 

Could that noise be the expansion valve operating?

 

They haven't used expansion valves in years.

BTW Rich, does the vehicle have the factory fan shroud? Is the vehicle running cool? I would check just in case. You may have a heat transfer thing going on.

 

The engine temp gauge has never went above the half way mark. Yep it has all of the factory stuff including the fan shroud. I know better than too operate a vehicle without a fan shroud! Did that before when I was about 16 years old, not good!

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Could that noise be the expansion valve operating?

It uses an orifice tube. it causes the liquid refrigerant to turn back into a gas. It doesn't use a temperature sensor to operate. just flashes the refrigerant as it passes through it.

 

Really, would you like to back that up with a source? Expansion valves are still used today on many automobiles.

 

Well I'm not here to argue about methods, but to throw out a blanket statement that expansion valves haven't been used for YEARS, is ridiculous. Many car companies use them, and you can't change how air conditioning works.

 

Yes, let me rephrase that..FORD (which last time I looked, is the type forum we're in) hasn't used them on "factory Installed" vehicles "in years". I worked for Ford/Lincoln for 20 years, I know all about expansion valves....and to this day never heard one....much less saw one jettison freon out of the system. If you want to get technical, we can get technical.

 

Some more info...

My radiator started leaking a bit from one of the plastic end tanks so I just decided to replace it. When I pulled the old radiator out about 20 -25% of it was blocked due to road debris & oily residue. The condensor wasn't though? Go figure. Anyways I'm sure that even though the condensor is in front of the radiator it still probally restricted some airflow. I made sure to spray the condensor out really well too. I think this could have been part of the problem.

 

No. I'd say that was 100% of the problem. With the restricted radiator, the air was not flowing through the condenser. It was deflecting off of it.