Dash A/C pretending it is a heater.

[Testdepth]

I've been following georgecederholm's post regarding his dash a/c unit failure and have gleaned a lot of good info from it. My problem is similar in that my dash a/c unit is just blowing warm air. Assuming(hoping) it was just low on charge because the compressor clutch was not activating, I put the gauges on it and I have zero pressure in the system! So now the fun part begins, finding the leak. Once that is done and repaired comes the evacuate and charge part. There in lies my major problem, I can't find a sticker anywhere that tells my how much r134a the system holds. there are a couple of labels on the compressor itself but nothing as to the charge. Up front I've crawled up inside the nose of this beast and do not see a label on the front end unit.

 

Does anyone know if there is a standard location for that label or a charge amount for this system?

Thanks in advance for any knowledge anyone can share.

Mike

1996 Monaco Windsor C8.3

No slides, no Toad

 

[Chuck B 2004 Windsor]

I experienced a similar failure.  I found out that when starting the coach and turning on the dash air, not enough air pas passing through the evaporator coil to regulate the high side pressure causing the Freon to leak out of the the ports used to install and monitor the Freon.   I waited for the radiator stack fan to come on before turning on the dash air.  Chuck B 2004 Windsor

[cbr046]

My HVAC tech buddy told me 30-40 psi on the low side would be good enough.  I brought mine up to 10 psi and 58F (20F differential) with Max AC & fan on HI when I checked it for the first time last week.  It took 2.5 cans and if it's still 10 psi I'll add a few more cans.  The PO told me the dash air didn't work so no telling how long it had been since it had a good charge in it. 

Of course I have a piercing type valve and now I need a "special" valve for self-sealing cans (flat pin vs sharp pin). 

As far as evacuating and starting over . . . . As long as air didn't enter the system IMO you'll be ok.  Of course, if you have the time and pump that's another story. 

The bad news is I get a lot of outside air coming in the coach at highway speeds.  The old F53 gasser leaked outside air too, but the HR is much worse.  Same for cold days.  I'd love to be able to find those leaks . . . .

Let us know where you find your freon leak.  Our HR's back end is over a bunch of rocks and not fun to crawl under.  Still chasing lots of other things too, like the back marker lights not working (fronts ok).  Yeeesh.

Best,

- bob

 

[Testdepth]

Thanks for the feedback Chuck and cbr046. I'm thinking (hoping!) my leak is Schrader valves. I pulled a vacuum (29") on the system and checked it after a couple of hours, no change. I left it overnight and only lost about 5" of Mercury so it is a pretty small leak. I put some dye in this morning and added 12 oz of refrigerant which was enough to give me enough low side pressure to engage the compressor clutch. I'm going to leave it at that and do some searching with a blacklight to see if I can find a leak. There's no sense dumping any more freon than necessary!

If I can't get any info on how much freon it is supposed to have I'll just guess by monitoring Low and High pressures and evaporator output temp and call it good. Not sure of any other way to do it.

Thanks again for the input.

 

Mike

[trailmug]

The Schraders seal well enough for you to get the caps on, but they aren't the primary seal.. if the caps are missing, you'll want some replacements. My low side pressure is pretty low with a full charge (20psig) owing to the long suction line.

It's difficult to charge these guys without recovering and weighing it in. If you have no capacity label, based on my experiences, I'd fill to 18F subcooling and then recover a pound. Capacities seem to vary a significant amount system to system.

Edited April 29, 2021 by trailmug

[Ivan K]

2 hours ago, trailmug said:

The Schraders seal well enough for you to get the caps on, but they aren't the primary seal.. if the caps are missing, you'll want some replacements. My low side pressure is pretty low with a full charge (15psi) owing to the long suction line.

It's difficult to charge these guys without recovering and weighing it in. If you have no capacity label, based on my experiences, I'd fill to 18F subcooling and then recover a pound. Capacities seem to vary a significant amount system to system.

Exactly my observation. Low suction pressure with good high pressure. Don't want it crazy high to achieve good low pressure with those 40' lines. I used about 4lbs of R134 while watching the gauges. But I evacuated and replaced the accumulator and expansion valve first. The problem with a leak is that you don't know how much oil might have been lost over time, so starting all over is safest. If you don't have an oily leak and still have decent static pressure per temp chart, leaky valves can be replaced with the valve tool without losing freon.

[Harvey Babb]

Leak location: my 2000 HR Endeavor had a cooked suction hose where it passed by the turbo. It deteriorated to the point that the hose felt crunchy if you moved it.

 

[Guest CjnCook]

In my 2008 Diplomat 40 PDQ, I had the same dash AC leak down issue. Charged by the dealer when I purchased the unit and it leaked down over 3 months. Charged it with 60 oz and leak sealant as the temp/pressure chart indicated. Leaked down again over 3 months. Borrowed a freon electronic and UV detector and started looking. But first I charged 12 oz of leak sealant, 6 oz of compressor oil and 60 oz of freon. Looked from one end to the other. Checked the evaporator thoroughly. Up at night with the UV light and glasses checking every square inch and searching down the tunnels where the hoses pass. No sign of leak detector or oil. After 3 weeks, no leaks detected. The unit is still showing a 15 degree drop. I am beginning to think my previous leak sealant did not have enough concentration of sealant for such a large system to do the job. This time the 12 full ozs of sealant may have done the job. That in addition to the oil charge may have "fixed" the problem. Another bit of info is the unit basically sat for a couple of years before my purchase and the compressor seal may have dried just enough to leak and is now good. Two hour drive last week in 65 degree weather and the unit was blowing out 52 degree cool air. I am thrilled about that.

 

JeffP 2008 Monaco Diplomat 40PDQ

[Testdepth]

So a little more info I’ve discovered. This coach has been sitting pretty much unused for the last 4-5 years so it’s quite possible compressor seals are dried out. After putting in is out 16oz of Freon my compressor did kick on and I had decent, ~ 20 psi lp side pressure my high side pressure was only around 100. I put an additional 12oz can with the stop leak in to see if I could get my high side pressure up thinking I’m just extremely low on Freon for so much piping. At this point I have 42 degree air from the center vent in front. Lp side at about 10 psi and Hp side still 100 psi. Now I take a drive and watch temp at vent. 60 degree outside temperature. My vent temp goes down to 31 deg. stays there for awhile the slowly climbs to 47deg. then cycles back down to low 30s. Continues this for the trip through the mountains where outside temp drops to about 50.

Should there be that much range in the temperature and is this even a valid test with such low outside temperatures?

Also with such low high side pressure I’m wondering if the compressor is weak. I will put gauges back in today to see if pressures are the same and tonight will start looking for the leak since I put dye in yesterday.

Thank you for the responses regarding pressures and possible leak points. I checked my piping path and it appears it stays on the opposite side of the engine from the turbo, but I know one line has to get over to the condenser in the radiator stack on the left side so will trace out that line today.

 

[Guest CjnCook]

Assuming you are using R134a, check to see if it matches the ambient temperature and pressures on the attached chart. At first glance, your system pressure seems low.

[Rikadoo]

So in my pre-retired life I worked in a Ford dealership, I would get F-550s, 650s, and 750s in which had cummins engines all of them had "for the most part" the same issue low on charge, some had no charge. Over the years I saw a theme low on charge with no signs of leaks ANYWHERE, meant though there was no signs of oil leaks, AND unable to find ANY freon leaks was determined to be from the compressor shaft seal, that while rotating from operation the seal would not be able to deal with the fluctuations of the pressures and therefor would become incontenent. Which if anyone has ever tried to locate a freon leak KNOWS there can be no movement of air or else you will not be able to get any accurate readings.

The other was if I discovered there was NO freon pressure in the system the first thing I would do is to drill a small hole in the evaporator case, then I would insert my borescope probe thru the hole and 9.8 times out of 10 would find that there was a leak, some small some not so small.

So my work with many of the automotive ac systems have proved several ideas of thought to me, 1st is all systems leak, and since the change from r-12 to r-134 I found that r-134 has smaller molecules as the Mfg. has in fact stated. That there trying to reduce that seepage is evident in the vehicle Mfg's had changed to different compounds for hoses, o rings and seals, there is no denying there is a seep/leak issue, it has been widely discussed thru trade rags for years.

So my street smarts that I have been able to develop over the years is this, Not if but When the system leaks now there is a "low state of charge" that when this happens the clutch now is cycling on / off more than usual, for years the customer always states "it quit cooling all of a sudden" and up intel then it had always blown cold! So a fact not many people know is that the oil within the system flows with the freon when In operation, and also when the freon level goes lower so does the flow of oil... Now when the freon level gets to a point that the compressor clutch is machine gunning that there is little if any oil getting back to the compressor, signs of this can be seen of seized compressors or as I discovered the shaft seals that expect to be wet have not had enough lube to keep them from glazing or worse.

This was why for my regular customers I would always every season sell a ac service, this was where I would connect the ac machine, do a performance check (monitor pressures while checking the duct temps) , then I would reclaim the freon, pull the system into a vacuum, add dye, then recharge to spec, then perform yet another quick performance check. Now FOR MY CUSTOMERS the package service offered up to 1/2 lb of additional freon to maintain spec charge, I WILL STATE that everyone one of those systems was always low 1/4 lb or more. 

Call it what you want, upselling, preventive maintenance, hype or whatever, what I can tell you is the systems that always had catastrophic failures NEVER had any annual services performed! Dealerships keep records on all work performed, for YEARS...

Now to return to when I discovered the Evaporator had failed, not only would I replace the Evaporator, I always replaced the compressor along with the accumulator. 

NOBODY likes to spend $$$ I get it, however if you have a savy mechanic he will offer that AC PM service, listen how they perform it, some may NOT reclaim then refill to spec, some just add a 1/2 lb with out checking, HOWEVER if they say they DID NOT ADD ANY FREON, then all they did was to look for leaks, turn the system on and felt it get cold, I have ALWAYS believed in the reclaim and refill to spec. That some say you can't make time doing it that way, On any given job IF I had the machine close to me (2 machines shared between 25 techs) I could make 1 to 2 tenths per job, which always gave me enough traffic of a/c work to be able to get other repairs.

[trailmug]

2 hours ago, Testdepth said:

So a little more info I’ve discovered. This coach has been sitting pretty much unused for the last 4-5 years so it’s quite possible compressor seals are dried out. After putting in is out 16oz of Freon my compressor did kick on and I had decent, ~ 20 psi lp side pressure my high side pressure was only around 100. I put an additional 12oz can with the stop leak in to see if I could get my high side pressure up thinking I’m just extremely low on Freon for so much piping. At this point I have 42 degree air from the center vent in front. Lp side at about 10 psi and Hp side still 100 psi. Now I take a drive and watch temp at vent. 60 degree outside temperature. My vent temp goes down to 31 deg. stays there for awhile the slowly climbs to 47deg. then cycles back down to low 30s. Continues this for the trip through the mountains where outside temp drops to about 50.

Should there be that much range in the temperature and is this even a valid test with such low outside temperatures?

Also with such low high side pressure I’m wondering if the compressor is weak. I will put gauges back in today to see if pressures are the same and tonight will start looking for the leak since I put dye in yesterday.

Thank you for the responses regarding pressures and possible leak points. I checked my piping path and it appears it stays on the opposite side of the engine from the turbo, but I know one line has to get over to the condenser in the radiator stack on the left side so will trace out that line today.

 

Yeah the thermostatic cycling is normal in a TXV system with low load. Since there's no cycling switch, there's a frost sensor on the evap that cuts out to prevent icing.

[Testdepth]

Jeffrey and Rik, thanks for your inputs. After looking at the ambient temp vs pressure chart and extrapolating down a bit, it appears to me that I’m still a bit low but not by a lot! From here I’m going to pursue leak detecting and just use it till our ambient temps get a little higher and then compare to the charts to see how it looks then.

BTW, pressures this am, 50degree ambient temperature, were about the same; 10-15 low side 100 high side. We’re supposed to get to 70 in the next day or two so I’ll do a check then to see if I get any increase in pressures.

thanks again.

Thanks Rob. I think Troubleshooting with outside temps so low makes it a bit more difficult. When our temps get a little hotter I should be able to get a better idea of how the system is working, and hopefully a more narrow temp swing.

mike