A/C help- compressor runs constantly, good pressure high side, no pressure low side

[teamsmith]

Hey guys,

'89 4.0 converted to 134A by previous owner.

My AC was working but the compressor would run constantly. After reading various forums, I decided I had a bad low pressure switch, the little two prong thing that sits atop the accumulator. I bought a new one but, when I went to replace it, all the refrigerant came out behind it (I thought I understood that there was a valve that kept the refrigerant in the accumulator, guess this one is faulty or stuck open). After that the engine blew so we swapped with new engine and, during removal, disconnected hard lines and removed condensor, potentially exposing lines to contamination while we figured out how to get the new engine installed. 

 

Fast forward: Using vacuum pump and gauges, we pulled a vacuum and leak tested (no leaks) and commenced to recharging. I ended up putting the full 38oz in the system per Chiltons.

 

Result: 

High side pressure: 150 psi @ 85 degrees ambient (chilton's says 120-180 @ 70 degrees ambient so I'm calling this 'normal') 

Low side pressure: 0 psi (it went into slight vaccuum when I closed the gauge valve). 

Vent temp: HOT - no noticeable cooling at all 

Compressor: runs constantly. Only stops running if I pull the plug from the low pressure switch. 

Sight Gauge: Can't see anything going on. Used to see some bubbles but maybe that was because there used to be water and now I've got it cleaned out. 

 

 

 

Thoughts? 

Could it be a stuck expansion valve? Is there anything that I can hit with a hammer that might loosen up? 

[mikekaz1]

stupipd question, have you tried depressing the shrader manually on the low side to see if theres actually any pressure there?

[teamsmith]

Where is there a schrader valve? I'm using the service ports on top of the compressor which are controlled by turning the stems. 

 

One thing I did not try, but plan to do later, is to let it run and see if can feel the lines. If the lines are cold up to a certain point or junction, I can assume there is a blockage. 

[Marine1Texas]

if your getting 0 psi in the low side you must have a blockage or a bad schrader valve. schrader valve is the pin that is compressed to allow exchange in service , you have 2 high and low

You may also have a bad expansion valve that would be bloacking Freon from entering or leaving the evaporator.

 

Freon starts off being sucked from low side thru the dryer to compressor then becomes high pressure then thru condenser to the expansion valve thru evaporator leaving the expansion valve to low side.

If your low side schrader valve is working and low to no psi, you may have blockage or a bad expansion valve

[teamsmith]

Ok ill check it out. Funny that I never noticed a Schrader valve on the lines, even when I pulled the engine out.

 

If I have no pressure on the low side, how would I tell if the valve is working?

I do recall that the evap canister was sweating but I never put my hand on it to feel of it was cold.

If it's a bad expansion valve, any chance I can swap out without having to evacuate refrigerant?

Is it possible to replace

[mikekaz1]

chances are anything that handles refrigerant. is impossible to replace without releasing the contents

[teamsmith]

That is what I figured but I know you can isolate the compressor and replace it without releasing the gasses. I hate that I just spent ~$50 on r134 but it isn't the end of the world. 

 

I still haven't had a chance to take another look at it but I am willing to bet it's a clogged expansion valve that will need to be replaced. 

[scguy]

Here's a tip, if the expansion valve is plugged, which it likely is, you'd better replace your filter drier also as it's likely come apart and plugged your expansion valve.

 

If you really want to fix it right, you should also flush the condenser and evaporator.

 

If you take it to a shop with a proper AC recovery machine, they might credit it back to you when you go to charge rather than just let the air have it. I really recommend getting it vacuumed and charged by an actual scaled machine.

[teamsmith]

I've been doing some more reading and have found that symptoms of a plugged expansion valve is a very high high side pressure (250+psi) but that is not my experience. Could it still be the expansion valve even though I'm not seeing high pressure? I'm reading alot of talk about a bad evap core and how much of a hassle that is to replace. What are the symptoms of a bad core? 

 

I feel pretty comfortable using the rental gauges and vacuum pump from AZ; are you saying they are not as accurate? 

 

At the end of the day, I do not want to spend alot of money here. I would rather poke around it on myself than pay a shop. 

[scguy]

I've seen an evaporator core do two things; leak or get plugged with dirt and have no airflow across.

 

If you're using a vacuum pump, that's good. Most people around here just shoot cans and call it done. It's still best to charge my weight and not by pressure, but with gauges and a sight glass, you can do pretty good.

 

Sent from my LG-H810 using Tapatalk

[teamsmith]

I've seen an evaporator core do two things; leak or get plugged with dirt and have no airflow across.

 

If you're using a vacuum pump, that's good. Most people around here just shoot cans and call it done. It's still best to charge my weight and not by pressure, but with gauges and a sight glass, you can do pretty good.

 

Sent from my LG-H810 using Tapatalk

Thanks. I followed the chiltons instruction guide to the letter on evacuating and pulling a vacuum, leak tested (no leaks), then charged with 38oz per Chiltons. 

 

On the evap core, I don't think it's leaking because it held a ~ 30 hg vacuum for nearly 10 minutes. If it was clogged, would I see what I'm seeing now? no low side pressure, normal high side, and the compressor will not cycle off? When I did my engine swap, I had the condensor removed from the truck for a couple weekends. the lines definitely could have become contaminated. I really hope I don't have to replace the evap core. I hope to spend some time with it this evening to see if I can feel where the lines are hot vs. cold. 

[scguy]

No, I was saying I don't think the evaporator core is your issue. Either you've got a faulty gauge reading or you've got a restriction on the low side

 

Sent from my LG-H810 using Tapatalk

[Marine1Texas]

I have seen evaporator core's plugged from a bad receiver/drier before. Most people do not pull vacuum and most try to get away without replacing the receiver/drier. Once a dyer is exposed to the humidity you get clumps that can form then break off. This normally builds up in the area that the expansion valve opens and closes near the low side.

 

Personally I would replace your receiver/drier, while it is open to the air. Most of the time if it is not leaking your compressor is good you have blockage or a bad valve.

 

Best bet go get 4 cans of 12 oz from Walmart for 20 bucks, they on sale right now for 5 dollars. get a new receiver/drier and a new set of orings. Get out your compressor and blow out the expansion valve, blow out your condenser and evaporator. with compressed air. You will not have to remove condenser or evaporator. make sure to push about 100 psi or better thru them both. I would also do the same and clean the hoses out. At the time you can see if you expansion valve is clogged or maybe stuck closed. once you can see everything is passing cleanly, put it all back together. then vacuum down your system. once sealed add your pag oil and then the 3 1/2 cans of 134a.

 

Most of the time the condenser and evaporator do not need to be replaced unless they have a leak. The weak area's of all ac systems are the ; expansion valve's, schrader valve's, receiver/drier, then the compressor.

 

If one develops a leak in a condenser and evaporator it only 2 things, movement/piercing from out side, or you have developed humidity in the system. humidity in the system will cause corrosion because alkaline levels become acidic.

 

This is why you I always recommend replacing a receiver/drier and vacuum the system down.

[teamsmith]

A

 

I have seen evaporator core's plugged from a bad receiver/drier before. Most people do not pull vacuum and most try to get away without replacing the receiver/drier. Once a dyer is exposed to the humidity you get clumps that can form then break off. This normally builds up in the area that the expansion valve opens and closes near the low side.

 

Personally I would replace your receiver/drier, while it is open to the air. Most of the time if it is not leaking your compressor is good you have blockage or a bad valve.

 

Best bet go get 4 cans of 12 oz from Walmart for 20 bucks, they on sale right now for 5 dollars. get a new receiver/drier and a new set of orings. Get out your compressor and blow out the expansion valve, blow out your condenser and evaporator. with compressed air. You will not have to remove condenser or evaporator. make sure to push about 100 psi or better thru them both. I would also do the same and clean the hoses out. At the time you can see if you expansion valve is clogged or maybe stuck closed. once you can see everything is passing cleanly, put it all back together. then vacuum down your system. once sealed add your pag oil and then the 3 1/2 cans of 134a.

 

Most of the time the condenser and evaporator do not need to be replaced unless they have a leak. The weak area's of all ac systems are the ; expansion valve's, schrader valve's, receiver/drier, then the compressor.

 

If one develops a leak in a condenser and evaporator it only 2 things, movement/piercing from out side, or you have developed humidity in the system. humidity in the system will cause corrosion because alkaline levels become acidic.

 

This is why you I always recommend replacing a receiver/drier and vacuum the system down.

Awesome. Thanks for all the advice. This is very helpful. So I should go ahead and order a new drier but hold off on getting a new expansion valve until I get the old one off and blow it out? What are the chances the expansion valve just needs to be blown out? I am tempted to just go ahead and get a new valve so I could make sure I could do all this in one day. Thoughts? 

[Marine1Texas]

If the expansion valve is cheap enough would not hurt much to just replace it, it will save you time in delay if it is really bad (the last time I replace with a 4-Seasons A/C Expansion Valve it cost me less then 20 dollars)  However I am not a guy who just throw's new parts at something. in the 25 years of doing commercial ac and home ac I say 10 to 15% the expansion valve really go's bad. Most the time I see them go bad, because oil was not added or acidic level from humidity cause the valve to corrode, do to previous bad maintenance not vacuum system down and new receiver/drier.

 

 

This is for those who can make or have access to making new hose and fittings.

Since I make all my own hoses, I just use the cheap 20 dollar receiver/drier that I use on home units. They use the #6 connectors as well as most cars do. the quick disconnect crap I got rid of, since if those fittings go bad, they are not as easy to get.

[teamsmith]

I have seen evaporator core's plugged from a bad receiver/drier before. Most people do not pull vacuum and most try to get away without replacing the receiver/drier. Once a dyer is exposed to the humidity you get clumps that can form then break off. This normally builds up in the area that the expansion valve opens and closes near the low side.

 

Personally I would replace your receiver/drier, while it is open to the air. Most of the time if it is not leaking your compressor is good you have blockage or a bad valve.

 

Best bet go get 4 cans of 12 oz from Walmart for 20 bucks, they on sale right now for 5 dollars. get a new receiver/drier and a new set of orings. Get out your compressor and blow out the expansion valve, blow out your condenser and evaporator. with compressed air. You will not have to remove condenser or evaporator. make sure to push about 100 psi or better thru them both. I would also do the same and clean the hoses out. At the time you can see if you expansion valve is clogged or maybe stuck closed. once you can see everything is passing cleanly, put it all back together. then vacuum down your system. once sealed add your pag oil and then the 3 1/2 cans of 134a.

 

Most of the time the condenser and evaporator do not need to be replaced unless they have a leak. The weak area's of all ac systems are the ; expansion valve's, schrader valve's, receiver/drier, then the compressor.

 

If one develops a leak in a condenser and evaporator it only 2 things, movement/piercing from out side, or you have developed humidity in the system. humidity in the system will cause corrosion because alkaline levels become acidic.

 

This is why you I always recommend replacing a receiver/drier and vacuum the system down.

 

so I finally got around to ordering a new filter drier and will be ready to do the install in the next week. One thing I noticed is that there is a charge on the filter /drier. I assume it's ok that I lose this charge when I do the install because I don't see any other way to connect to the lines without first removing the caps. 

[teamsmith]

 

I have seen evaporator core's plugged from a bad receiver/drier before. Most people do not pull vacuum and most try to get away without replacing the receiver/drier. Once a dyer is exposed to the humidity you get clumps that can form then break off. This normally builds up in the area that the expansion valve opens and closes near the low side.

 

Personally I would replace your receiver/drier, while it is open to the air. Most of the time if it is not leaking your compressor is good you have blockage or a bad valve.

 

Best bet go get 4 cans of 12 oz from Walmart for 20 bucks, they on sale right now for 5 dollars. get a new receiver/drier and a new set of orings. Get out your compressor and blow out the expansion valve, blow out your condenser and evaporator. with compressed air. You will not have to remove condenser or evaporator. make sure to push about 100 psi or better thru them both. I would also do the same and clean the hoses out. At the time you can see if you expansion valve is clogged or maybe stuck closed. once you can see everything is passing cleanly, put it all back together. then vacuum down your system. once sealed add your pag oil and then the 3 1/2 cans of 134a.

 

Most of the time the condenser and evaporator do not need to be replaced unless they have a leak. The weak area's of all ac systems are the ; expansion valve's, schrader valve's, receiver/drier, then the compressor.

 

If one develops a leak in a condenser and evaporator it only 2 things, movement/piercing from out side, or you have developed humidity in the system. humidity in the system will cause corrosion because alkaline levels become acidic.

 

This is why you I always recommend replacing a receiver/drier and vacuum the system down.

 

so I finally got around to ordering a new filter drier and will be ready to do the install in the next week. One thing I noticed is that there is a charge on the filter /drier. I assume it's ok that I lose this charge when I do the install because I don't see any other way to connect to the lines without first removing the caps. 

 

I'm bumping my question regarding the filter/drier coming with a charge on it and whether it is ok for it just to release. I will be installing this weekend and there is nothing in Chilton's regarding this particular task. 

[mikekaz1]

I don't see how you would be able to install without loosing this charge.  I believe its more for internal protection while in transit and storage.

[Marine1Texas]

If your talking about a charge in a new filter. it is not a charged it is pre vacuum down so that it keeps moister and dirt out! Like mikekaz1 says for transit and storage reasons.

[teamsmith]

I don't see how you would be able to install without loosing this charge.  I believe its more for internal protection while in transit and storage.

 

That was my take as well, unless there is some kind of device required (of which I am unaware) that somehow maintains it during install. 

 

Yours and Kudo's responses are what I needed for my quick sanity check. I'll wait until I'm just about to do the install before opening up the plugs. 

 

Thanks guys!