Jump to content

Dash Air Compressor Always On?


Recommended Posts

For the past 3 years I have been having problems with my dash air.  We've searched high and low trying to determine were the system was leaking freon.  Once again, after replacing the fittings at the compressor, there seems to be a leak in the system.  I think this is going to be an ongoing problem.

My question for today is why the compressor is always energized even when I turn the dash control to heat/vent.   No matter what position I turn the selector switch to from the off position the clutch kicks in and runs the compressor.  I would think it would only be energized when the selector is turned to Air or Max Air.  Should I unplug the control wire at the compressor during our winter travel?

Gary B.

2002 Monaco Windsor, PBDD

Link to comment
Share on other sites

Like FishAR says, compressor is there to remove humidity.  Defrost mode too.

You should have leak dye put into the system.

I would power wash the entire system front to back first.

Then, when the air stops cooling again, look for dirt collection.  That dirt may be the oil in the system leaving which then attacts dirt.

The leak dye might also help find the leak with a UV light.

Likely whoever is replacing seals, didn't find the actual leak if it persists.  Or they are putting the wrong oRings on the joints (too small).

What happens is someone puts the wrong seal on and it then leaks.  Then the second mechanic replaces with the same size and it too leaks.

You just have to find a decent AC repair (auto is same as RV) that will methodically diagnose the issue and not just slap a part on an call it good.

There's no magic involved...just tenacity.

Edited by DavidL
Link to comment
Share on other sites

Thank You all so very much.  I figured it had to do with removing the moisture especially in defrost mode.  I'm afraid I still may have a leak in the system.

I have taken it to a highly rated mechanic in Ft. Myers for the last 2 years.  They have cleaned the entire system, flushed and evacuated the system, replaced the compressor, dryer and connections and recharged the system twice with freon and luminescent leak detector.  The system works well on my way back to Iowa each spring but by summers end is low on freon.  My mechanic here in Des Moines, who has worked on my vehicles successfully for years can't seem to find the leak either.  Last week while I was there we found the 2 new fittings at the compressor replaced in Florida this past February were both sucking air as he tried to draw a vacuum. 

We the ends replaced and the vacuum holding we recharged  the system with freon and dye.  Since it was cold outside he charged it with 4 lbs. of freon.  We couldn't find any specs on the number of pound required.  He said that way I could add more when reaching a warmer climate much easier with a hose and can from the auto parts store.  Any one know how many pounds of freon a 40 ft.  Monaco Windsor requires??

We have not been able to access the lines running through the coaches center channel to the front of the coach.  I guess my next step is to try to remove the ceiling panels in the bay compartments to access the lines for testing.

Gary B.

2002 Monaco Windsor PBDD

Link to comment
Share on other sites

IMO, electronic leak detector is the only way.. oil doesn't always leak out unless it's a huge leak. Monaco field assembled the hoses using manual crimpers, I'd bet lunch it's leaking at a crimp joint (well, at least one), as you've been finding. My discharge hose would only leak when the system was operating, and it held vacuum fine. Took me a couple of years to find it, and the first replacement fitting also leaked. If you can, avoid crimping onto the old hose wherever possible (have short hoses or short segments of long hoses made at a hydraulic shop), and if you have to for the long hoses, I recommend fittings from Gates. They fit much better than what you can get through MEI, for example, in my experience.

IMO, barrier hose is very unlikely to develop a slow leak in the middle of a run.. it has a solid sleeve of nylon on the inside. You can get to most of the hose except the area where it passes over the fuel tank, but I wouldn't bother unless you're replacing it.

I'd disconnect the pressure switch at the receiver; that way the compressor connector is still watertight.

In case it's interesting, I've seen it suggested that cooling performance doesn't suffer until a system loses 60% of its charge. That was certainly the case for me when I discovered my last leak.. only recovered 2 of 4 lbs and it was still cooling fine. 

Edit: sorry, my browser wasn't showing the latest posts. 

Edited by trailmug
Link to comment
Share on other sites

Pictures: bad crimp (puckered out MEI fitting), good crimp (Gates fitting), ParkerStore discharge hose I had made with Gates crimp fitting attached. Both crimps made with the same MasterCool manual crimper. 

 

 

received_201116144262668.jpeg

received_3279628802049890.jpeg

received_288711362161730.jpeg

Edited by trailmug
Link to comment
Share on other sites

"nanny poka dot bowtie engineers"

I installed a compressor cut out switch such that I, the rightful owner, can decide when I want to run the AC compressor. There are a lot of AC problems discussed on this forum , many of which I suspect are due to the stupid system running most all of the time. Much of that time is a complete waste of machinery and whatever fuel 3-5 hp consumes. One could collect the amount of condensate produced by the system in a dixie cup on a dry day in the West

Ford decided that I wasn't smart enough to know when to use my fog lights with my high beams. So they  disable the lights when using high beams. Fog lights help define the edge of a narrow dusty or muddy road when using high beams. Lot of muddy roads in Oregon. I thought everyone knew that.

Fixed that little problem also.

I have something for them right here.

 

Edited by Gary Cole
Link to comment
Share on other sites

On 10/19/2021 at 1:29 PM, burghere66 said:

For the past 3 years I have been having problems with my dash air.  We've searched high and low trying to determine were the system was leaking freon.  Once again, after replacing the fittings at the compressor, there seems to be a leak in the system.  I think this is going to be an ongoing problem.

My question for today is why the compressor is always energized even when I turn the dash control to heat/vent.   No matter what position I turn the selector switch to from the off position the clutch kicks in and runs the compressor.  I would think it would only be energized when the selector is turned to Air or Max Air.  Should I unplug the control wire at the compressor during our winter travel?

Gary B.

2002 Monaco Windsor, PBDD

No. It's never a bad thing for the AC compressor to run. Here's why. The seal on the compressor is lubricated with oil. It is the oil that is the primary seal keeping the R134a refrigerant in the system. So if you leave the system un-used for a period of time, that oil will dissipate and the refrigerant will leak out. While it's true that there is parasitic HP loss with the compressor running, in our diesels you will never see that in the mileage calculation - period. In a car, yes, if you're very accurate in your measurements. Also, the older the compressor, the less parasitic loss.  

Having said that, on our 2000 Diplomat the AC ran in odd positions on the dash dial. Can't remember which. It was on sometimes when it should have been off and off sometimes when it should have been on. As such, I installed a switch to override the dash switch and allow manual control of the compressor (see pic). 

I used to a lot of MVAC (motor vehicle AC) and got it down to a science. Unfortunately, not many shops know how to do good AC (which is why I spent the time developing a diagnostic process). First, most shops recover and then pull a vacuum and then look at the analog gages to see if there is any rise over time that would indicate the system is leaking and sucking in air. The problem is, an analog gage is very coarse and will not show minor leaks even if left overnight. The proper way to do it is with a properly sealed Thermistor Micron Vacuum gage. It will measure vacuum down to the micron level which is extremely precise. Generally speaking, if it will hold 750 microns, or less, for 15 minutes, it's not leaking under vacuum.  That leaves leaking under pressure.....

To check for leaking under pressure you need access to the entire system AND a very good leak detector. Most shops have no idea what constitutes a good leak detector. They buy whatever Snap On tells them to. By and large, the industry standard is one that was originally made by GE, probably back in the 50's, and then updated along the way. It's been licensed to a whole bunch of companies but is often known as the Yokogowa/Mars/Bacharach HP10. It will reliably pick up very small leaks under pressure but you have to have access to the entire system. GM used to send it to all the dealers as a mandate - every dealer had to buy one - it was considered an essential tool. It just showed up and the dealer paid 400% more for it then they could have bought it for themselves. 

In your case, because you cannot easily access the lines from the rear to the front you have to diagnose it by exclusion. So, if a shop used a thermistor micron vacuum gage, and it held, you would know the entire system has integrity from front to rear under vacuum. That leaves pressure. If they charge the system, operate it, and then shut it down and hit it with the HP10 you can access everything *except* the lines from rear to front. Point being, if there is an issue with the lines you can determine it by exclusion. Evaporator leaks can be very slow, best way to test them is run the AC, shut it off, let it sit for 10 minutes, and then stick the probe in one dash vent, close all the others, put the fan on the lowest setting, and then run the fan on lowest speed to blow the pooled refrigerant up to the probe and see if it picks up a leak. All switches should be unplugged and the leak detector probe put in the mating hole to see if it goes off. You'd be surprised how many of them show a leak that way. 

It's also worth knowing that General Motors released a bulletin years ago stating that the Schrader valve service port caps are considered the *primary* seal. Ie, not the Schrader valve itself but the cap. This is because they understood that the valves themselves can leak trace amounts and is the reason the caps have a large rubber seal on them. It's literally a tandem seal. 

I'm up in Canada but when I was doing MVAC there was only one peer in North America that did work like I did and that was Arizona Mobile Air. The owner is Tim and if you find yourself in that neck of the woods, they can nail it - they have all the same equipment I do, and *tons* of experience. If I remember right, they used to buy their refrigerant by rail car..... Back when I was dealing with them there were 4 people in the US that did work like mine and they were all affiliated, in one way or another, with Arizona Mobile Air. 

But bear in mind, even if you have a system that has perfect integrity under vacuum and pressure, and it sits unused for long enough, the oil on the compressor seal will eventually drain off and the system will leak refrigerant. This is very common in earth moving equipment that sits over the winter. They fire it up in the summer and cook in the cab because the refrigerant leaked out. When you go on the job site there is no leak. Not under pressure and not under vacuum. Why? The oil ran off the seal during the winter and it leaked out. The minute you recharged it and ran it as part of the diagnostic process that seal got coated in oil again....and presto...it's hermetically sealed once more. 

One of the reasons they made AC systems come on during defrost was so that the systems would be used more often and keep that oil coating the compressor seal. The other reason is that blasting the fogged windshield with dehumidified air speeds the defrost procedure. With modern vehicles the AC is usually always on. On my Mercedes roadster it actually cannot be turned off. There is no clutch (so that the end user never hears a 'clack' as it engages and disengages) and instead it uses a variable swash plate. So even when it is off, it's still working, just at a very low level. This keeps the seal lubricated and on vehicles like that, typically there are NO AC issues until the compressor packs it in. So even if it's -40c in Russia (they have lots of these cars over there) the AC still runs. The oil in the compressor is high-end synthetic and is carried along by the refrigerant. 

I used to own an automotive shop and never did AC because it was, typically, a money loser and the chances of a comeback were very high. When you see a regular shop that has an AC machine it's almost a warning sign.....When I retired from that I went into MVAC more as a hobby and to come up with a diagnostic procedure to address the industry standard AC repair failure rate of 50%.....to do it properly you need a shop with a Thermistor Micron Vacuum gage and an HP10 leak detector. Unfortunately, even HVAC people don't always understand the importance of those two items.....

Just for the record, I found that even with our dash AC and heater working properly, the design and the load are just too much without being able to enclose the cabin. As such, I run the genset if it's summer and use the roof AC units. If it's winter, the furnace plus the dash heat. Your mileage may vary. 

Anyway, just some tips and background info to help you in your quest!

20211020_224426.jpg

  • Like 1
Link to comment
Share on other sites

On a system that works well, the compressor doesn’t run all the time as there is a frost sensor in the evaporator that keeps the fins from icing up by shutting off the 12V to the compressor. From my experience it shuts the compressor off more than necessary, not just on my MH. On my air conditioned equipment I pull 50% of the cap tube (sensor) out of the evaporator coils so the compressor doesn’t shut off as often. Instead of on for 30 seconds and off for 30, it’s on for 45 and off for 15 increasing the cooling substantially.

On my MHs I rarely have to run the generator/ACs as I completely bypass this sensor by plugging the two wires into a 15A fuse so the compressor does run all the time. Out West it usually takes 6+ hours before enough ice forms that the air volume starts to decrease while running the fan on high. In the East (higher humidity) I have to shut off the extra switch I added to the 12V compressor circuit every couple hours (for 15 minutes) to defrost the evaporator fins…you still get cold air as it melts the ice.

On my 08 Navigator I had one crimp at the fill port that was not crimped enough… tried a portable crimper  unsuccessfully and finally stopped the leak by adding 2 small exhaust C clamps over the crimped area after splitting the sleeve in 3 areas with a cutoff disk.

Edited by Ivylog
Link to comment
Share on other sites

The one case where I'd disagree with running the compressor after summer is in OP's case of a known leaking system. I don't trust the binary switch to fail open, because I've seen my (reasonably new) switch still closed when the system was under vacuum.

Well, and on my Cadillac, where the short-cycling of the system during winter due to close proximity to the frost point caused a constantly wet and musty-smelling evap.

Edited by trailmug
Link to comment
Share on other sites

11 hours ago, Bob Jones said:

oil coating the compressor seal

Thanks for the information Bob. Very interesting. Learned a lot. The only question I have is how long the oil will last on a seal under normal conditions. Based on, my understandably limited experience with classic cars and cars in storage, it seems to be a very long time.

Edited by Gary Cole
Link to comment
Share on other sites

20 minutes ago, Gary Cole said:

Thanks for the information Bob. Very interesting. Learned a lot. The only question I have is how long the oil will last on a seal under normal conditions. Based on, my understandably limited experience with classic cars and cars in storage, it seems to be a very long time.

That depends on compressor/seal design. Some are worse than others. Also, wear on the seal (mileage) and amount of oil in the system come into play. If you have accurate enough equipment you can recover the charge, weigh it, and extrapolate the loss. It gets a bit complex because you have to be able to scrub the oil from the recovered refrigerant to get an accurate number. It's much easier, from a diagnosis standpoint, to do it by exclusion. If it does not leak under vacuum or pressure, where did the refrigerant go? At that point you suspect the seal. If you ask the customer if the vehicle sat for a period of time, 9 times out of 10 they will tell you they were out of the country on a trip or something like that. This is why you *have* to have the proper gear. When doing diagnosis by exclusion you have to know, 100%, that you have excluded *everything* else. 

Just because the AC works on an old vehicle that sat doesn't mean the charge is not low.....if the charge is low it will not carry the oil through the system as effectively. In addition, the oil can be low as it tends to leak out with the refrigerant. This is why you sometimes see an oily trace with dirt stuck to it around a leak. If a system is low on refrigerant and oil then you are starving the compressor and damage/early failure is easily possible. 

As the compressor wears it will tend to send metallic material through the system...... When you pull the orifice tube out of a CCOT system you will often see metallic material on the screen. That can be used as a gage as to whether a compressor should be replaced. When a compressor fails catastrophically it will send enough metallic material through the system to plug a modern parallel flow condenser. If you don't replace it the material will eventually break loose, get sucked into the new compressor, and damage that one....So there is a lot to it. AC repairs, proper ones, tend to be expensive. My motto was do it once and do it right. If a person could not afford to do that, I weeded them out right over the phone and they were grateful because they didn't waste any money chasing something they could not afford. A lot of people think you can just buy a 'death can' and charge it back up. The system has to have integrity and the correct charge in order for the oil to lubricate the compressor. Other wise you are just damaging the compressor by starving it for oil as the system leaks out again. 

AC repairs are generally not cumulative. The industry stats when I was doing it was a 50% failure rate. This means the customer loses their investment if it's not done right the first time. That's not 100% accurate in all circumstances but it's pretty close. You can put an inline filter on the suction line going to the compressor to catch debris. What is interesting is that I deviated from the established norm and publicly stated it's better to put it on the discharge line if there has not been a compressor failure. The idea being that as the compressor wears, or if it explodes, the debris will be stopped on the discharge side before it reaches the rest of the system. I took a lot of flack for that 'heresy' back in the day. 

Oil level in the system is the real challenge. There is no accurate way to determine how much oil is in the system especially when it's an old vehicle that may have been serviced before. There are rules of thumb, if replacing the condenser add this much, etc. But the only way to really determine oil level is to flush the entire system with liquid refrigerant and then scrub the recovered oil from that refrigerant flush. GM specified that only refrigerant could be used to flush a system, nothing else. If a person can flush the entire system with liquid refrigerant than you know it has no oil other than what is left in the compressor, because it cannot be flushed in a closed loop. So you still have to take the compressor off and drain it into graduated cylinder to see what was actually there....

Proper MVAC AC is tough and not many shops can do it. If you think about the labor time involved in what I've been describing it gets expensive fast. Up here the average low bill was $500. If a customer got an effective repair for that, they were laughing. $1,500 was the common price point, almost all repairs fell into that bracket. $3,500 was usually the top end. At that point it was more/less complete system replacement. Replacing the evaporator alone in a Volvo required removing the entire front interior including seats, console and entire dash. Suburbans with rear air have lines from front to rear that tend to corrode (road salt) and the rear evaporator would often leak. It was not uncommon to have to do both evaporators and the lines from front to rear plus the regular under the hood work. 

Can't tell you how many people had their AC done multiple times with the result being a lighter pocket and warm air. I live in a relatively affluent area so my customers were happy that they finally found someone that could do it once, and do it right, warranty it, and then be done with it. And that's in Canada, where it's a relatively cool climate for the brunt of the year. I can't even imagine what it's like in Arizona. I do know that my peers down there told me you can get 3rd degree burns if you touch the dashboard in your car if it's been sitting in the parking lot at the mall for the afternoon. One of my peers was a cooling system design engineer for one of the big three and he told me with every new model they took it to death valley to verify the cooling system and the AC system. Up here it's hard to image that AC can be essential. 

 

 

Link to comment
Share on other sites

I purchased a very low mileage 1996 300ZX, last year sold in US, at auction with what had clearly been multiple attempts to repair a non operating AC. When I called the local Nissan dealer to inquire about repairing the system he asked if I had a blank check.

Link to comment
Share on other sites

It's very good of them to warn you. This is what I did to everyone over the phone and I saved them from going down a path they didn't want to/could not afford to go down. I turned away at least 60% of potential clients. But here's the thing, I wasted no time and had only very happy customers that had money and just wanted it done right. They also have more than one car, so they could leave it at my leisure. They told all their friends, and next thing you know, they would cut me off in mid speech and say just do it, don't care about the price (within reason). In fact, my sales method probably caused them to tell their friends!

If you still have the Nissan, and want to repair it, consider buying some of your own gear and doing it yourself. Typically, you can buy a lot of the equipment for less than the repair if you are so inclined. Two days ago I scored a brand new H10PM off ebay for $99 USD ($200 CAD shipped). This was unusual but it can be done. O-rings are cheap. Jap cars are usually well designed. Could easily be o-rings or what have you. If it's low mileage compressor should be fine. If it's never been in a front end accident the condenser is probably OK. In the US parts are cheap (Arizona Mobile Air). You might be surprised but it's a lot of fun (usually) and it's very rewarding doing something well that 50% of the people can't do. Time is the biggest thing. Not being on the clock. 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...