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A/C is dead but odd symptoms?


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Hey gang! I'm having issues with the A/C system in my truck. This may take a while and make a long post but I think the context and symptoms may help the diagnosis. About a year ago when I'd turn the A/C on there would be a light smell coming out of the vents. It smelled to me like poplar leaves in the fall after they come down mostly dried up. SWMBO though it reminded her of old books bound in the 1950s and stored together in a closed room. It didn't linger long, maybe a minute or two would clear it out and all would be well. A/C performance was good at this point. I was thinking that maybe I had some poplar leaves down in the cowl that I needed to dig out. Never got to that part... I now believe that this smell is the PAG oil used to lubricate the compressor. Fast forward to a few weeks ago and we got a nice hot spell again and I hopped in the truck to go home from work and wouldn't ya know? No A/C! Drat! I've been reading a lot about A/C systems as this is the first one I've had an opportunity to work on. I'm pretty sure I have a dead evaporator and very low refrigerant level. Here's what I've seen so far: 1. A/C clutch cycles rapidly when A/C controls activated but no cold air is produced. Evidence of a bad Low Pressure Switch or low refrigerant level. 2. Tested the low pressure switch (LPS) per the procedure from the FSM. Switch checks out OK, but exhibits opposite behavior than is expected; no continuity when the compressor is on but there when compressor is off. I think this indicates that the suction side has high pressure when off but low when on, indicating a low charge of refrigerant. 3. High pressure switch checks out OK. 4. When the LPS is bypassed with a jumper wire so the compressor runs the condenser inlet gets quite warm. I don't have a way to measure how warm but it's hotter than you want to stick your finger on. At the same time the condenser outlet line is ambient temp until the rear edge of the passenger side battery. At that point it abruptly turns ice cold and begins to collect frost on the the length of the line all the way back to the firewall. Still no cold air. Seems like there may be a clog somewhere but how would that happen on a system that's never been touched? 5. I borrowed a set of gauges from Autozone. They looked brand new but I wonder if they had issues. When I connected them to the truck in the proper manner I could not get a pressure reading of any sort on the high side or the low. According to the gauges, there was no pressure at all whether the compressor was running or not. When I disconnected the hoses and broke the setup down for storage there was trapped pressure in the hoses that escaped and made me jump. Was not expecting that! LOL Clearly, there is something trapped in the lines! I cannot find any evidence of leaks under the hood based on the notion that a refrigerant leak would also carry the PAG oil with it and leave a stain on a leaking fitting or damaged line. This leads me to believe that the evaporator in the cab is the culprit. I would like to be sure before I go tearing into that particular can of worms. Is it possible to have a leak in the evaporator that releases enough R-134a out to prevent cold air making but keeps enough in the system to chill a line to ice maker level? This seems contradictory to me. Does anyone know off hand what PAG oil smells like? Buying some from the parts house just to smell it seems like a waste of money to me since I will not be performing my own recharge. That is one task I will hire out to an expert! Thanks in advance!

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Hey gang! I'm having issues with the A/C system in my truck. This may take a while and make a long post but I think the context and symptoms may help the diagnosis. About a year ago when I'd turn the A/C on there would be a light smell coming out of the vents. It smelled to me like poplar leaves in the fall after they come down mostly dried up. SWMBO though it reminded her of old books bound in the 1950s and stored together in a closed room. It didn't linger long, maybe a minute or two would clear it out and all would be well. A/C performance was good at this point. I was thinking that maybe I had some poplar leaves down in the cowl that I needed to dig out. Never got to that part... I now believe that this smell is the PAG oil used to lubricate the compressor. Fast forward to a few weeks ago and we got a nice hot spell again and I hopped in the truck to go home from work and wouldn't ya know? No A/C! Drat! I've been reading a lot about A/C systems as this is the first one I've had an opportunity to work on. I'm pretty sure I have a dead evaporator and very low refrigerant level. Here's what I've seen so far:

 

1. A/C clutch cycles rapidly when A/C controls activated but no cold air is produced. Evidence of a bad Low Pressure Switch or low refrigerant level.

 

2. Tested the low pressure switch (LPS) per the procedure from the FSM. Switch checks out OK, but exhibits opposite behavior than is expected; no continuity when the compressor is on but there when compressor is off. I think this indicates that the suction side has high pressure when off but low when on, indicating a low charge of refrigerant.

 

3. High pressure switch checks out OK.

 

4. When the LPS is bypassed with a jumper wire so the compressor runs the condenser inlet gets quite warm. I don't have a way to measure how warm but it's hotter than you want to stick your finger on. At the same time the condenser outlet line is ambient temp until the rear edge of the passenger side battery. At that point it abruptly turns ice cold and begins to collect frost on the the length of the line all the way back to the firewall. Still no cold air. Seems like there may be a clog somewhere but how would that happen on a system that's never been touched?

 

5. I borrowed a set of gauges from Autozone. They looked brand new but I wonder if they had issues. When I connected them to the truck in the proper manner I could not get a pressure reading of any sort on the high side or the low. According to the gauges, there was no pressure at all whether the compressor was running or not. When I disconnected the hoses and broke the setup down for storage there was trapped pressure in the hoses that escaped and made me jump. Was not expecting that! LOL Clearly, there is something trapped in the lines!

 

I cannot find any evidence of leaks under the hood based on the notion that a refrigerant leak would also carry the PAG oil with it and leave a stain on a leaking fitting or damaged line. This leads me to believe that the evaporator in the cab is the culprit. I would like to be sure before I go tearing into that particular can of worms.

 

Is it possible to have a leak in the evaporator that releases enough R-134a out to prevent cold air making but keeps enough in the system to chill a line to ice maker level? This seems contradictory to me. Does anyone know off hand what PAG oil smells like? Buying some from the parts house just to smell it seems like a waste of money to me since I will not be performing my own recharge. That is one task I will hire out to an expert!

 

Thanks in advance!

Edited by Rebelrodder
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I would gladly do the work on the A/C system. But I'm sure your no where near me though...

 

If there is less than 25 PSI lo side the system will not start. Now the lower the lo side pressure the colder it gets so if you jumped the low pressure switch to start it it will most likely freeze up. R134a should be about 35-40 PSI on the lo side and about 225-275 PSI on the hi side. Kind of hard to have a system pumping without pressure on either hi or lo side. :think:

 

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I appreciate your willingness but, yeah, we"re about a 12 hour drive apart. That's a long way to go! =)

 

I agree, there's gotta be something left in the lines otherwise, how could there be any cold anywhere? I think I'll try to get a different set of gauges to see if I can get anything that way.  

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  • 1 month later...

Update time!

 

I finally got a chance to get some different A/C gauges and take some pressure readings. With the compressor off I read about 30 PSI in both ports. With the compressor on I got about 65 PSI in both ports. According to the FSM that means that the system is low on refrigerant or empty. I'm leaning toward low because it can still create ice on the line going to the evaporator. That tells me there is at least some R-134 left in there.

 

Does it make sense that the evaporator would be leaking but that the R-134 would not be all gone? That really doesn't make sense to me. The R-134 is a gas right? So a leak in the system should let all of it out until there is none left. Or am I over thinking this? Not that I've ever been accused of that! :ashamed:  

 

I'm only guessing that the evap. is the problem based on the smell in the cab and the lack of oily residue on any of the system connections under the hood. The FSM recommends using an electronic sniffer to verify before spending money on parts but Autozone doesn't have one for rent. Would anyone recommend going that far to absolutely verify the issue or just go with the best guess method? Also, would it be a good idea to have a mechanic recover any remaining R-134 before I start working on the system? 

 

Thanks in advance for any advice sent my way!

 

Jerrod

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Before I went and started throwing parts at it I would find a shop (could even be a HVAC/R shop) and have them go over the system with an electronic sniffer. If you were close to me you could use mine and do it yourself.

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My speculation is that you are smelling possible mold of some type.  Make sure your evaporator pan drain is open.  I blow some compressed air through the drain where the condensate water exits.  This is my opinion.  On truck like we have that are this old, you can and should expect leaks of some kind in the A/C system.  Depending when or if you have ever added refridgerant, it may have taken MANY years for the system to leak down to its current status. 

 

I am speaking from the hard learned experience of my wallet.  The first time my got low, I took it to the dealer thinking it would be a fairly quick diagnosis and repair.  HAAAAAAAHHHHH!!!!  It was just an expensive "diagnosis" (notice the sarcastic quotes :rolleyes: )  All they did was put more refridgerant with dye added in my truck's system and told me to bring it back.  I did and they still could not find the leak. 

 

Long story short, the first time I bought a bottle of the refridgerant with oil and sealant at Walmart.  It worked for almost 2 years.  The next time I just added more refridgerant.  As long as the leak is reasonably slow I think it is much cheaper in the long run to just top off the system when it gets low.  Now, if the system leaks down to ZERO, that is an altogether different story.  You need to evacuate the system and recharge it with some dye mixed refridgerant and find the leak and fix it.  Having to add a can of refridgerant to bring the system up to par every few years is not a big deal and the best way to go overall in my opinion.  Yes I realize that the book method is to have the entire system evacuated down, recycled, and have a measured amount of Freon and oil added per the manual temperature tables.  The cost of doing this will buy cases of refridgerant, gauges, and an evacuator. 

 

Eventually, whatever is slowly leaking will probably turn into a big leak and you will have to replace/repair the part/leak.  Until then, I would just keep it going.  Use it up, wear it out, make it do, or do without.  Hope this helps. 

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LiveOak,

 

Mold would kinda make sense actually. I'll check to see that the pan drain is open  and free flowing. If the mold is infesting the evaporator, is there a way to clean without taking the evaporator out?

 

I gather you are saying that it is possible for R-134 to leak out slowly over time and not leak out completely. Is that right? Seems counter intuitive but I will admit to being an HVAC newb!

 

I think I'll make sure that the cowl area is free of debris and the drain is clear then grab a can of that recharge stuff this weekend and give that a shot. Even if it only gets me through until spring that'll be better than sitting in a cold damp truck all winter!

 

Thanks for the advise!

 

Jerrod

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I would recommend that you use a shop vac to clean the A/C drain. If you use compressed air it will blow that snot like stuff that gets in the drain back into the air box. A vacuum will suck it out.

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A vacuum  sounds like a good plan to me. I looked for the drain and wondered how I'd get a blow gun into the top to clear it out. I figured that I would not want any stuff getting pushed back into the HVAC unit. Just to be sure I'm looking at the right part, the drain is just behind the accumulator in the fire wall. Yes? Can the accumulator be removed from it's bracket and gently slid out of the way to gain access to the drain? My hands are fairly small but I doubt I can get much down there behind it. 

 

I did get a recharge can from the parts store the other day but now we're in a cold snap so I can't test the system to see if it's working now. It's too cold outside for the PCM to turn the compressor on. I may have to wait until spring to get suitable weather again. We'll just have to see!

 

Thanks for all of your help!

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