Thanks, I'll inspect wiring. If it's an intermittent thing like it seems then that makes sense.
Accumulator/dryer really cold even when AC is off
- Thread starter ripcord
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- May 17, 2021
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"I got out of my OBS Ford truck after about a 20 minute drive this evening and noticed that there was a drip coming out of the back of the engine compartment. I popped the hood to find that the accumulator was covered with a heavy layer of condensation. The weird thing was that the AC was off and I haven't turned it on in that rig for weeks."
AND:
"It was pretty mild - mid seventies. Also, it's an old truck without automatic climate controls. The only other detail that comes to mind was that I parked it on a hill all day with the front facing down."
I'm sticking with my original analysis: Liquid refrigerant had moved to the receiver from other parts of the system but when you drove home temperatures became such that the liquid boiled away, cooling the receiver below the dew point and leading to condensation on the outside surface. However I've spent a ridiculous amount of time thinking about this neat little thermodynamics problem and I don't think the conditions would be easy to recreate.
Step 1: Parked in the sun so front of truck and cab get pretty warm. This drives the liquid to the receiver which is cooler than either the evaporator or condenser. 'Cooler' could be very slight -- just a couple of degrees would do it over the course of a day.
Step 2: Drive home, air is cooler and moist. Passing over the receiver the air is cooled below the dew point and condensation occurs.
The problem with this is that where the refrigerant is condensing -- either the condenser or evaporator -- must be cooler than the receiver so it would have to be even more below the dew point. Why didn't moisture condense there? Two possibilities that I can think of:
A. 'There' isn't in the same airflow. That would most likely be the evaporator -- the air going through the condenser is warm from heated pavement but you had the windows open so the cab's cool from air higher up, and the vapor boiling off in the receiver is moving to the evaporator. This might be especially likely after a shower because the warm air near the ground would be saturated with moisture.
OR:
B. Moisture is being added to the air flow passing through the engine compartment: Venting from the radiator overflow tank, or a tiny leak, you passed through a puddle and the radiator and/or engine got splashed, something like that.
The combination of conditions needed to make this work would not be easy to reproduce but those are the parameters. Fluid-filled receiver, then moist air at a temperature higher than 'somewhere else' in the system passing over the receiver. The hard part is that the temperature difference has to be enough to take the air below the dew point at the receiver.
Aside from OP's statement that A/C had not been on, what makes the 'clutch engaged' idea not work is that under those conditions the receiver gets warm, even 'ouch!' hot. Nothing's going to condense there.
I'm afraid I won't quickly forget this problem. Maybe someone with broader experience will have a more definitive answer.
AND:
"It was pretty mild - mid seventies. Also, it's an old truck without automatic climate controls. The only other detail that comes to mind was that I parked it on a hill all day with the front facing down."
I'm sticking with my original analysis: Liquid refrigerant had moved to the receiver from other parts of the system but when you drove home temperatures became such that the liquid boiled away, cooling the receiver below the dew point and leading to condensation on the outside surface. However I've spent a ridiculous amount of time thinking about this neat little thermodynamics problem and I don't think the conditions would be easy to recreate.
Step 1: Parked in the sun so front of truck and cab get pretty warm. This drives the liquid to the receiver which is cooler than either the evaporator or condenser. 'Cooler' could be very slight -- just a couple of degrees would do it over the course of a day.
Step 2: Drive home, air is cooler and moist. Passing over the receiver the air is cooled below the dew point and condensation occurs.
The problem with this is that where the refrigerant is condensing -- either the condenser or evaporator -- must be cooler than the receiver so it would have to be even more below the dew point. Why didn't moisture condense there? Two possibilities that I can think of:
A. 'There' isn't in the same airflow. That would most likely be the evaporator -- the air going through the condenser is warm from heated pavement but you had the windows open so the cab's cool from air higher up, and the vapor boiling off in the receiver is moving to the evaporator. This might be especially likely after a shower because the warm air near the ground would be saturated with moisture.
OR:
B. Moisture is being added to the air flow passing through the engine compartment: Venting from the radiator overflow tank, or a tiny leak, you passed through a puddle and the radiator and/or engine got splashed, something like that.
The combination of conditions needed to make this work would not be easy to reproduce but those are the parameters. Fluid-filled receiver, then moist air at a temperature higher than 'somewhere else' in the system passing over the receiver. The hard part is that the temperature difference has to be enough to take the air below the dew point at the receiver.
Aside from OP's statement that A/C had not been on, what makes the 'clutch engaged' idea not work is that under those conditions the receiver gets warm, even 'ouch!' hot. Nothing's going to condense there.
I'm afraid I won't quickly forget this problem. Maybe someone with broader experience will have a more definitive answer.
Sorry if I'm keeping you awake at night and thanks for giving it a think or two. 
I drove the truck to work and back again today duplicating the route, the parking spot, etc, trying to make it happen again, but both subsequent days the accumulator has been dry and just a little bit warm to the touch. I checked when I got home and the AC is blowing nice and cold so I guess I'll chalk it up to a fluke for now and see how it goes.
I drove the truck to work and back again today duplicating the route, the parking spot, etc, trying to make it happen again, but both subsequent days the accumulator has been dry and just a little bit warm to the touch. I checked when I got home and the AC is blowing nice and cold so I guess I'll chalk it up to a fluke for now and see how it goes.
I'm not familiar with the AC system on his particular vehicle but he stated that the condensation was on the accumulator and I assumed that is in fact what he has. An Accumulator would mean it is located on the low side of the system and would get cold while the system is running. If it is not an accumulator and is in fact a receiver drier on the high side then yes it should not get cold and get condensate on it. But then again a receiver drier could get cold if there is a sufficient change in pressure across it from being clogged up or restricted. If the problem continues I don't think he would have a difficult time confirming that his compressor is stuck on.
This is the part that was cold. I was calling it the accumulator or receiver/dryer but feel free to correct me if I'm wrong.
This is the part that was cold. I was calling it the accumulator or receiver/dryer but feel free to correct me if I'm wrong.
what year/model/engine/etc truck is it so I can look up the part myself and confirm what type of system you have.
It's a 96 Ford F-250 with the 5.8l
well I'm confused.. looked that up on rockauto and they list both a thermal expansion valve and orifice tube available for that truck. You would use one or the other just like you would use a receiver/drier or an accumulator accordingly. Based on the images of that particular part it looks to have a low side port on it though it is hard to be sure without anything to compare it to for size. I'm going to guess and say it's an accumulator but it's hard to be sure without actually seeing it and how the system is routed. Based on the images I've attached it looks like an AC line runs along the top of the firewall from the compressor to the "accumulator". If that is indeed the case then it is indeed on the low side and is an accumulator. A receiver/drier would be connected on the high side between the condenser and evaporator instead.
edit: looking at other engine bay pictures on google image search does show a direct connection between the accumulator and compressor so that confirms what it is.
Attachments
That's what I've got
That is an accumulator.
American SUVs and vans with rear air have an expansion valve for the rear, even though the rest of the system is accumulator / orifice tube. The valve closes down when the rear fan is off, allowing the front system to continue to operate normally.
American SUVs and vans with rear air have an expansion valve for the rear, even though the rest of the system is accumulator / orifice tube. The valve closes down when the rear fan is off, allowing the front system to continue to operate normally.
These trucks never came with an expansion block or valve with factory ac. Orifice tube only with factory ac. Also none had rear ac. The dealer add on units did sometimes use a valve or block.
So I swung by a buddies and we used his AC machine to evacuate the system - turns out it was 10 ounces low on refrigerant (had 28 ounces and calls for 38). If it has a leak it must be super slow as he couldn't find a leak with his sniffer. I couldn't really tell any difference in how cold it was blowing as it seemed OK before adding. Also, no idea if this had any bearing on the weird behavior with the cold accumulator, either.
