AC Recharge

[Venturer]

I just had the inoperative dash AC diagnosed and found a bad compressor which was replaced with a new one. It worked great, for a while. When I adjusted the temp dial from very cold to less cold, it started blowing very warm air. Turning the dial back to max cold had no effect on the temp. I shut it off for 30 minutes. When turned back on, it blew cold air as it should. That sounds like a mixing valve/door issue to me. The more important problem is that after 4 days of cooling, the air became less and less cool eventually reaching the same temp as OAT. That seems like a slow leak in the system. I'm thinking I could buy a set of gauges to check and recharge the system myself till I can get back to the shop that did the work to find the leak. What is the recommended Recharge kit to use? I see some with a can of R134a, gauge and hose to add to the low-pressure side which seems simple enough. However, without knowing the high-pressure side, isn't it possible to get it too high?  It's been 30+ years since I did this with our farm tractors and combine, so I'll need to reeducate myself. 

[CAT Stephen]

Doug,

Recharge kits are dangerous because you don't know the pressure on the high side.  The only way to properly troubleshoot R134A dash air issues is to purchase or rent an R134A manifold gauge set so that you can see what is going on inside your system.

Safety is your first priority because skin and eyes exposed to refrigerant can cause permanent blindness and severe frostbite.  Carefully review R134A refrigeration procedures and wear PPE (Personal Protective Equipment) including goggles, heavy rubber gloves, and thick protective clothing to avoid potential injury.

 

Here is the R134a manifold set that I recommend and use for troubleshooting and recharging my dash AC:

- https://www.amazon.com/Robinair-49134A-Aluminum-Manifold-Couplers/dp/B004QA7MAQ/ref=sr_1_5?crid=280KN8ZD4HLKX&dib=eyJ2IjoiMSJ9.niWEEk7ybVGXv1I5FktRIICq-Xw6UbOkBLRkQLwZhpIRVXC8jGjMYdaWRkwtdY0bQVYCp4chFrJk40Ub4D_QbIf93om1BF7f_L2FRcjj93vAf8FKZuEUXqtazobzrZbLaHZBLbX4L7r32FqdR5iWwSsaQH0hpJKTJU22Ji07w99ENhrZ1NWM7EeHERC7g8mBSbAr1SdHhHmspNDtHE68n9xQsS8nlG826ATz0AQbck3RJs6cPYddPiYgVILDPYCxKm6QYnSTyaAKjrbwZvnvE8ninvLdxmgZ1UfY1S3bpZk.styWWQziatFT9W-ygmHZX71dLOJKtDQgOsrIr3ZDOYo&dib_tag=se&keywords=r134%2Bmanifold%2Bgauge%2Bset&qid=1715285365&sprefix=R134%2Bmanifold%2B%2Caps%2C186&sr=8-5&th=1

[Venturer]

After I wrote the above post, I saw how cheap the recharge kits are and went to my local NAPA store and purchased one. It's similar to what you recommended, but with shorter hoses and no case. When the weather warms up a bit, I'll see what I have for pressures. Hopefully, it's a small leak and not the new compressor failure. 

[cbr046]

I just got mine back today.  I had overfilled the system and trashed the compressor (locked solid).  Compressor, dryer, expansion valve, freon, 10 hrs of labor . . . It was a *VERY* expensive mistake.  They added 52 oz of R134 . . . I thought it took 42 or 44 oz, but they said they got it from a sticker somewhere. 

First thing after getting home was check high / low pressures to see what it should be.  Static pressure measured 66 psi (high and low sides).   Turning on AC and full blower showed 102 / 24 psi (high/low) at 600 rpm and 124 / 19 psi at 1200 rpm,  temp was 64F.  The shop measured 50F from the outlets (80F ambient) yesterday, 30F differential (which is pretty good).  If I lose freon I can go back and add just enough to get to these levels. 

So don't do what I did, but do get yourself cool again 😎 .

- bob

Edited May 9 by cbr046
added ambient temp for pressures

[jacwjames]

I have a chart in my owners manual that shows pressure based on ambient temp. 

[Venturer]

7 minutes ago, jacwjames said:

I have a chart in my owners manual that shows pressure based on ambient temp. 

The gauge set has a chart with it. I didn't realize that different ambient temperatures resulted in different pressures.

[cbr046]

7 minutes ago, jacwjames said:

I have a chart in my owners manual that shows pressure based on ambient temp. 

I have that chart also - 64F, added that to my post.  The 80F ambient was yesterday so the pressures don't match the ambient. 

- b

[Tom Cherry]

2 hours ago, cbr046 said:

I have that chart also - 64F, added that to my post.  The 80F ambient was yesterday so the pressures don't match the ambient. 

- b

FWIW….these pressures and temperatures are in the older manuals.  From a practical standpoint, based feed back from a few members….and one I KNOW understands how to test and add and restore to “factory”; you have to have the MH under cover…..and in building or garage that is “open”….  Then, it is best to leave the MH overnight to stabilize or “SOAK”.  Next morning, turn on the AC and let the dash run until, generally speaking (slides in or course….bathrooms closed…bedroom door shut) the interior is cooled to a point that the cockpit temp is close to the galley….in other words….the interior is gonna be as COOL as it will be….based on the charge.  THEN, you do the interior (closest to the main vent) measurement.  TECHNICALLY the control should NOT be in Max COOL as that shuts down the outside air damper.

RARELY will you find a shop that will follow the “theoretical” conditions which the chart was published on.  But…if you do this like a lab experiment…and MATCH or duplicate the “design or factory” test….the temperatures and pressures will come close.

OK….why is this important and what difference….does it make.  Simple…you are chasing your tail and your frustration will increase.  

REAL WORLD…I had a buddy come over.  An experienced and “certified” HVAC tech.  BTW, he has an electrical engineering degree for UofPITT and worked for GE at a high level position among other jobs.  NO DUMMY. He made a lucrative investment in a “startup” GE and other electrical supply business.  He and his buddies sold…and none of them every worked again. He got bored….went to the community college and learned HVAC and helped out his neighbors and also fixed the units on the beach properties he bought…for income.  Took the state test…passed…he also, for fun, became a highly sought HS Basketball REF….OH, he played QB in college and was a multiletterman in HS.

He tried every trick in the book.  He had NEVER worked on a MH out in 85 or 90 DEG ambient….that had SOAKED all day in the southern sun with reflection from my super white new concrete driveway.  He gave up, but we put or forced MAYBE 1 1/2 cans in it….

BTW… That was 3 years ago…and it is dropping a little…but did NOT, to the best of my recollection, damage the compressor.  My shop has done that 3 times…typically no more than say, 1 1/2 cans….as I ASKED.  They had a bulk tank, but weighed before and after….read on….

OK…mad and frustration aside…I kept it at home and finished the other projects….drove it to storage….that was 20 miles.  Left the HVAC Tech pocket thermometer in the outlet.  Now I cheated…max air.  LO & BEHOLD…I glanced at the thermometer.  Can’t recall the numbers….but i had increased the Delta T by at least 10…maybe 12 or more degrees.  I had COLD AIR….not lukecool air. I called a member…he MIGHT chime in.  We talked…he said my analysis was right.  In order to use, properly, the chart, you had to go through the conditioning and soak test and be in an enclosed (no sun bearing down) building.

He had a minor leak….undefined, but needed a recharge boost every 3 years or so.  Mine was similar….as are many here. Neither one, I THINK, ever pulled a vacuum and purged and refilled…like Monaco did.  BUT from a common sense and comfort level, he usually picked up at least 10 Deg Delta T and the air was cold….when you out your hand on it.  

I recently had the unpleasant experience of helping my GS find a “good” used car.  MEMORY…a GOOD system on max cool on a normal (80 deg) day will deliver 45 deg air.  We drove 25…no exaggeration.  He soon learned….if it didn’t feel cool and was not below 50….and the “dealer/owner” said….”JUST HAD IT TESTED AND RECHARGED”…that the individual was less than trustworthy.

MY TAKE.  It works for me…and mine sure cooled better….never got NEAR the pressures and temps…but I saved several hundred and it cooled just like my trusted OTR shop “fixed or recharged it”…..and I always tested the temp driving back to storage…

[Venturer]

Thanks, Tom, for your comments. I have it under our RV port here in WI so it's out of any direct sunlight. It's supposed to be in the 70's on Sunday and will hookup the gauges then to see what I have. It should be an easy check and recharge as the fittings are right at the new compressor. Hopefully, I will just have to add some R134 to get it cooling again.   

[trailmug]

Make sure the condenser fan is running, could be cooling until it goes off on high head pressure? Also make sure the expansion valve isn't getting icy.

I hope they flushed the lines GOOD when they did the compressor.. I had to use like two gallons of naptha. The sludge was unbelievable (I think somebody ruined it with old R12 mineral oil UV dye).

Oh, and the heat dial on mine is a water valve, not an air blend door, so it takes for frigging ever for the heater core to cool down once you let some hot coolant into it. Like a few minutes. 

In my experience, it is nearly impossible to get the correct charge on these units without weighing it into an evacuated system. The hoses are long and relatively thin, so superheat/sub-cooling measurements and suction pressure as measured at the rear service port will not be helpful, and the liquid receiver blunts head pressure response until it gets filled up (way overcharged). Somewhere where the pressures stay relatively steady while adding refrigerant is the butter zone.. Maybe if you had a sight glass before the evaporator.. some of the older liquid receivers have a crummy one built in. I wrote up a big ol collection of dash a/c notes in the files area 😁

Edited May 10 by trailmug

[dennis.mcdonaugh]

My dash AC hasn’t worked for 8 years. I just run the generator and house AC. The dash AC, when it did work, blew plenty of cold air, but didn’t do a whole lot to cool the coach when temps got above 70 degrees. 
 

When we were looking at buying a coach, we didn’t understand why we kept seeing curtain rods behind the front seats. They were an attempt to keep that small amount of cold air coming out of the dash AC in the front of the coach. 

Edited May 10 by dennis.mcdonaugh

[Venturer]

I hooked up the gauges and found that without the engine running, there was zero pressure on the high side and 25 psi on the low pressure side. When engine running, the compressor will not engage which is telling me the freon is too low. To recap: Two months ago, I had a shop check the system. They did a Nitro fill, peg oil w/dye and found the compressor leaking. Replaced it with a new Sanden, did an AC flush, vacuumed and recharged the system. All seemed well. With that service having been done, can I just add R134a until the pressures reach their correct levels for the OAT? That's assuming the compressor will engage when there is enough refrigerant in the system to safely run. Years ago. I just added R12 till the bubbles disappeared in the site glass. I haven't looked for the site glass but have the gauges now.

Edit: I realize I need to find the leak and correct it. I'd prefer to have the shop in AZ do the work, as they know the system and their rate is half of what is charged here for RV service, however, we won't be back there till Oct.  

Edited May 10 by Venturer

[Ivan K]

With zero pressure, chances are good that you already have air in the system as it breathes with temperature changes. You said there is a dye in it, maybe you can find the leak before wasting 4lbs of freon that will just leak out again. Anyway you decide, I stop filling when high pressure is correct at the compressor with our long lines.

[jacwjames]

Did you change the dryer????

 

[Venturer]

Yes, the dryer was changed. I just tried adding R134a to the system. After I was able to get some into it, the compressor clutch engaged and I thought I was on my way. However, the high pressure would not come higher than 50 psi while the low showed 10 psi. I could only get it to take about 8-10 oz of coolant. After shutting the engine off, the low pressure settled at 35 but the high remained at 50. After sitting for 10 minutes, the pressures remain the same. Is this telling me my new compressor is bad??

[trailmug]

Sound like a huge leak, running high pressure should be triple digits. 

0 high 25 low doesn't make sense. Sorry if this is condescending, but make sure you are turn the service port adapters clockwise to depress the service valves when reading/filling. 😁

[Ivan K]

At your starting pressures of 25/0, the system was empty. What you put in is a small fraction of what should be there. The compressor isn't necessarily bad just needs way more Freon and at 10 psi on low side it should really be sucking it in. Don't worry about the unequal stationary pressures, they take time to stabilize with a tight valve.

[Venturer]

3 minutes ago, trailmug said:

Sound like a huge leak, running high pressure should be triple digits. 

0 high 25 low doesn't make sense. Sorry if this is condescending, but make sure you are turn the service port adapters clockwise to depress the service valves when reading/filling. 😁

Both high and low hoses of my kit have 90 degree valves and both are open. Otherwise, I wouldn't get any reading. I'm puzzled as to why it won't take any more than 8 oz and the high side does not build pressure over 50. I would think the pressure would drop after shut down if there was a major leak.

[Tom Cherry]

10 minutes ago, Venturer said:

Both high and low hoses of my kit have 90 degree valves and both are open. Otherwise, I wouldn't get any reading. I'm puzzled as to why it won't take any more than 8 oz and the high side does not build pressure over 50. I would think the pressure would drop after shut down if there was a major leak.

Ivan or others will have to chime in.  We had the same issue...after we depleted the first can.  My buddy moved or positioned or maybe "beat - shook" the second can and it started to raise the pressure.  I DO REMEMBER that the second can took MUCH LONGER to start to impact the pressure than did the first.  Almost like the compressor or system was getting "FULLER" and that slowed down the filling.  NOW, does this work off a large cylinder or "propane tank" style source....and is different?

BUT, that is what I recall.  If I can sort out the specifics and the "trick", I'll post...but he said it was a common problem on cars...and knew how to get in a second can...but it was, I think, slower...and NORMAL...

[trailmug]

Yah, charging gas is slow, and if it's empty, one can will only be enough to get vapor pressure into the system, no liquid and definitely no cold air. System capacity if using 12 oz cans would be close to six of them. If it's leaking that quickly, there should be an oil stain somwhere. Check all the hose crimps, they're poorly done. If you can't find it, suspect the evaporator.

 

Withl a little luck, your 0 PSI high means it's a high side leak and doesn't involve the evap. Attached is a photo of a leak. 

 

Edited May 10 by trailmug

[Venturer]

After sitting for a couple hours, the low was 30 and the high was 50. Virtually no change. I started charging again and was able to get some more 134 into it. Maybe a total of 18-20 oz. The OAT is 65 degrees and the AC vent is at 39 degrees for a 25-degree drop.  This all seems so odd when the compressor wouldn't even engage due to being so low to cooling 25 degrees with only 1 1/4 16 oz can of 134 added. Now, the standing pressures are 25 on the low and 75 on the high. When running, the high is at 110 and the low is near 10.       

[Tom Cherry]

21 minutes ago, Venturer said:

After sitting for a couple hours, the low was 30 and the high was 50. Virtually no change. I started charging again and was able to get some more 134 into it. Maybe a total of 18-20 oz. The OAT is 65 degrees and the AC vent is at 39 degrees for a 25-degree drop.  This all seems so odd when the compressor wouldn't even engage due to being so low to cooling 25 degrees with only 1 1/4 16 oz can of 134 added. Now, the standing pressures are 25 on the low and 75 on the high. When running, the high is at 110 and the low is near 10.       

UPDATE....from my Buddy.  What he did on mine....NO SUCKEE OUTEE the GAS.  He turned the can upside down.  That, YES, puts LIQUID in...but he says that it turns to vapor or GAS instantly.  That is HOW he got MOST of the SECOND CAN IN. It also speeds up the recharging....just WATCH the pressures and "understand" what is happening...

ONE TRICK I USE...  Weigh the can (that works for a FULL Aerosol can) first...postal scale...nearest 1/10 of an ounce.  Read the NET WEIGHT.  SO, if a can weights 14.0 OZ and the NET is 8.0....then you know that it will weigh 6.0 when fully emptied.  Lets you KNOW exactly HOW MUCH went in...

Good Luck...

[Ivan K]

At 65F, the pressure in the can should be about 80psi. Same for the low and high after it eventually stabilizes, which may take long time. When you start filling, the low gauge should jump way up from the 10 that you report, is it so? You could wiggle the can between vapor and liquid and see the pressure changing. If it stays at 10 while filling, there is a restriction in the schrader valve or gauge valve. I am actually surprised that the compressor does not kick out at that pressure, it should. Your high side needs an other 25 psi to be at the lower end of range for 65F, so you are slowly getting there. I have never filled a system that has air in it, so no practical experience in that case.

[Venturer]

After another attempt, I was able to get the high up to 145 psi which is in the range for 67 OAT, however the low wants to stay near 10. After I shut it off, the high drops to 100 and the low settles at 25. The vent temp is now 37 degrees which is 30 below the OAT. The cooling is fine, but I don't think the low pressure is where it should be while running @1000 rpm.  Am I wrong?? I'm going to let it sit overnight and see what I have tomorrow. So far, I have used four 12oz cans.

Edited May 10 by Venturer

[Ivan K]

With 4 cans you should be right around where you should be. 145 is good at that temp and if your gauges are at the rear, on the compressor,  don't push it past top high pressure. The long lines from evaporator mess with the low pressure reading. If you have a low port up front, you could compare. Nothing to worry about the static pressures, it only means that your expansion valve is closed and compressor isn't back leaking.