Dash A/C issues in a U280

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Dash A/C issues in a U280

September 05, 2015, 09:56:43 pm

Our dash A/C has issues..... this seems to be a popular topic on the forum and I have read many of the post. So far I haven't hit on the right fix to the problems.
First : the air isn't cold enough, the compressor runs, high side line gets hot, low side is cool and sweats coming out of the evaporator. Low side pressure is between 45 and 55, ( only have the cheapo low pres gauge that comes with the 134a refill from Advance Auto) Condenser fans cycle on at 55 and off at 45, not sure if this is normal?

Second : The compressor doesn't cycle off unless I unplug the T-stat at the bottom of the evaporator. I expected it to cycle off after a few minutes, the gauge on the refill bottle shows the pressure normal for an 85* ambient.

Third : heater "H" valve? It is vacuum operated and the line "T"s with the vacuum operated outside air damper in the bottom of the evaporator/heater core box. If vacuum is present the heater valve and the damper operate as the should. The damper closes and the heater valve either opens or closes......not sure which?? and I don't understand why they would be operated by the same vacuum line? I am considering installing a ball valve in the 3/4" heater lines at the engine before they go up to the front. This should eliminate the possibility of a bad heater valve.

Any suggestions?

Re: Dash A/C issues in a U280

Reply #1 – September 05, 2015, 10:50:33 pm

Get a set of gauges--you waste your time and others just shooting in the dark without good information and data.

Make sure you have good airflow.

Cycling off could be high pressure, if there is a high pressure switch. Could be low pressure. Could be thermostat.

No guages means no info means throwing darts.

Re: Dash A/C issues in a U280

Reply #2 – September 06, 2015, 08:54:25 am

Quote from: krush – September 05, 2015, 10:50:33 pm

Get a set of gauges--you waste your time and others just shooting in the dark without good information and data.

Make sure you have good airflow.

Cycling off could be high pressure, if there is a high pressure switch. Could be low pressure. Could be thermostat.

No guages means no info means throwing darts.

OK, sure don't want to waste anyone's time.

I have a set of gauges but they have the old R12 hoses, most of my vehicles are older and converted to 134a. I need to get the 134a quick connect hoses for them. I'll do that soon. I also wanted to know the proper operation of the vacuum operated fresh air damper and heater valve. They operate together from the same vacuum hose.

I'll get new hoses for my gauges and post back when I have good data, Thanks

Re: Dash A/C issues in a U280

Reply #3 – September 06, 2015, 09:01:19 am

Look at your R 12 gages on the low side gage and see if it has a 134a scale on it. If it doesn't you will need a pressure temp chart so you csn convert the scale.

Re: Dash A/C issues in a U280

Reply #4 – September 06, 2015, 10:01:39 am

Here's what I have. Mastercool makes good stuff. There are some cheaper alternatives on amazon, but I don't know the quality. It also comes with adapter to use your gauges on a 30lb tank. Buying by 30lb is much cheaper. Amazon.com: R12-to-R134a A/C Manifold Conversion Kit: Automotive

As an Amazon Associate Foretravel Owners' Forum earns from qualifying purchases.

Re: Dash A/C issues in a U280

Reply #5 – September 06, 2015, 11:57:02 am

Our dash air isn't working either, so I'll be watching this post closely. Going to wait till we get it home to though. We're still in Vegas.

Re: Dash A/C issues in a U280

Reply #6 – September 06, 2015, 02:34:20 pm

Without guages can you measure outside temp and ac dicharge temp. You should see a 20degree difference. Thats about the best you expect.

Re: Dash A/C issues in a U280

Reply #7 – September 06, 2015, 03:39:45 pm

Actually on recirculate, you want to measure temperature delta between return air duct (foot area passenger's side) vs center duct with engine at least at 1100 RPM. And 20 degrees F is a reasonable number. If very humid, expect a little less. If very dry, a little more. It takes a lot of BTU's to condense water.

Re: Dash A/C issues in a U280

Reply #8 – September 06, 2015, 08:35:59 pm

See my post here that talks about dash A/C troubleshooting and more (it points to two other posts): Testing the dash air conditioning system expansion valve in a 1995 U300

Re: Dash A/C issues in a U280

Reply #9 – September 06, 2015, 10:36:35 pm

Quote from: stump – September 06, 2015, 09:01:19 am

Look at your R 12 gages on the low side gage and see if it has a 134a scale on it. If it doesn't you will need a pressure temp chart so you csn convert the scale.

They are R12 & R22 only, probably 30 years old, I have ordered R134A gauges today.
The dash A/C cools, just not very well and the condenser fans cycle a lot.
I will tackle the vacuum vent problem later, air changes from defrost at windshield to floor and dash vents whenever it wants to.

Re: Dash A/C issues in a U280

Reply #10 – September 14, 2015, 10:41:18 pm

Well.... I put the gauges on the coach Sunday, the outside ambient temp was 79 ( an overcast day here in FL.) I let the engine idle (750rpm) about 15 min with the AC on max, outside damper was closed, return air temp was 76, outlet air at center vent was 71, only a 5 deg diff. The condenser fans cut on at 48 on the low and 235 on the high side. Pressures began to drop and the fans cycled off at 42 low and 180 high. They continued to cycle on and off at these pressures consistently. Inside temps remained the same and after another 15 min I shut down the A/C and engine, let the system balance and read 95 on both low and high gauges.

Does anyone know if a 95 U280 has a TXV or a fixed expansion valve system? If a TXV, how do you check for a defective one?

Re: Dash A/C issues in a U280

Reply #11 – September 15, 2015, 02:47:47 pm

Not being there, I can't get at true feel, but what you describe appears to be a low charge. BUT, on my u270, the low pressure swtich has been bypassed.

TXV's usually get clogged for fail stuck. When they get stuck closed or clogged, your low side pressure will drop a lot.

Now, the reason I believe my low side pressure switch was bypassed is because my there is a thermostat swtich at the evaporator. Also, my low side runs very low....I believe this to be because of lack of airflow across the evaporator. FT used very small ducts.

You could jumper the low side pressure switch and monitor the gauges to see where they stabilize. Just make sure the high side doesn't go too high.

Re: Dash A/C issues in a U280

Reply #12 – September 15, 2015, 03:46:38 pm

The best place to ask for air conditioning information is at a dedicated A/C forum. A very good source of information is the forum at Automotive Air Conditioning Bulletin Board • Index page . I have received help in the past from one of their members who posts as "Nacho." Another good forum is Automotive AC Information Forum - ACKITS.COM .

In general, I think your engine should be running at about 1500 RPM when checking the system for cooling effectiveness, and I believe a good system should be able to achieve around a 40 degree temperature at the outlets. As far as I know Foretravel systems use a TXV rather than a fixed orifice tube.

Re: Dash A/C issues in a U280

Reply #13 – September 15, 2015, 08:56:19 pm

Look on top of your filter dryer in between the line connections. see if you see a small sight glass window.If you have one wipe it off.Hook up your gages and start up engine turn on ac fan on high.look in the sight glass, do you see bubbles? If so add refrigerant untill glass clears. A/c should be cooling better post gage pressures on here.

Re: Dash A/C issues in a U280

Reply #14 – September 15, 2015, 09:35:36 pm

"You could jumper the low side pressure switch and monitor the gauges to see where they stabilize. Just make sure the high side doesn't go too high"

Krush,
The only pressure switch I have found is the one on top and center of the condenser coil, it should be the high pres switch and I believe is the control of the condenser fans as the cycle on as pres rises and off as the condenser cools and pres drops. If I jumper the fans to run constantly the pressures are stable at 40 low and 175 high ...... but that is at idle (750 rpm)

D.J.,
Thanks for the link, Ill check out the forum, also I will try checking at 1500rpm next time, looking back at this thread I see the Brett had mentioned doing a check at 1100 rpm.

Stump,
No bubbles..... sight glass appears clear,
I would like to know if the fans are supposed to cycle so often, on and off with the aforementioned pressures every couple of minutes?

Thanks for the replies.....

Re: Dash A/C issues in a U280

Reply #15 – September 16, 2015, 07:05:10 am

Quote from: stump – September 15, 2015, 08:56:19 pm

Look on top of your filter dryer in between the line connections. see if you see a small sight glass window.If you have one wipe it off.Hook up your gages and start up engine turn on ac fan on high.look in the sight glass, do you see bubbles? If so add refrigerant untill glass clears. A/c should be cooling better post gage pressures on here.

This sight-glass technique doesn't work well for systems using R134a. A properly-charged R134a system will still probably show some bubbles in the sight glass. If there are no bubbles in an R134a system, then the system if probably overcharged--and cooling will be degraded.

Re: Dash A/C issues in a U280

Reply #16 – September 16, 2015, 07:13:30 am

Is your System originally a 134a system or a R 12 system that has been converted?
Do you have a digital thermometer like a fluke etc with a probe you can strap to a refrigerant line?

Re: Dash A/C issues in a U280

Reply #17 – September 16, 2015, 07:52:12 am

Review the wiring diagram. When the condenser fan turns off, does the compressor stop spinning too? It should, according to most diagrams I saw.

Re: Dash A/C issues in a U280

Reply #18 – September 16, 2015, 09:06:08 am

Quote from: stump – September 16, 2015, 07:13:30 am

Is your System originally a 134a system or a R 12 system that has been converted?
Do you have a digital thermometer like a fluke etc with a probe you can strap to a refrigerant line?

It's originally 134a from FT
It has the system sticker on the evap box.

Re: Dash A/C issues in a U280

Reply #19 – September 16, 2015, 09:12:28 am

Quote from: krush – September 16, 2015, 07:52:12 am

Review the wiring diagram. When the condenser fan turns off, does the compressor stop spinning too? It should, according to most diagrams I saw.

Compressor doesn't cycle off with the fans. Only when the T-stat is satisfied on the evap, it doesn't get cold enough to satisfy so I unplug one side and the compressor shuts off.

Re: Dash A/C issues in a U280

Reply #20 – September 16, 2015, 09:16:25 am

Quote from: stump – September 16, 2015, 07:13:30 am

Is your System originally a 134a system or a R 12 system that has been converted?
Do you have a digital thermometer like a fluke etc with a probe you can strap to a refrigerant line?

I have a Fluke 87 but I haven't hooked the thermocouple probe to a refridgerant line. Not sure what those readings should be?

Re: Dash A/C issues in a U280

Reply #21 – September 16, 2015, 11:12:22 am

Quote from: FourTravelers – September 15, 2015, 09:35:36 pm

I would like to know if the fans are supposed to cycle so often, on and off with the aforementioned pressures every couple of minutes?

The condenser fans cycling on and off sounds as if they are wired through a "trinary switch" which turns them on at a high pressure and off at a low pressure. I believe on some vehicles the condenser fan(s) turn(s) on when the system is turned on and then stay(s) on until the system is turned off. Obviously, the compressor clutch needs to cycle on and off.

I do wonder if your system is overcharged, which decreases R134a performance. A 40 degree low-side pressure translates to a temperature of about 45 degrees at the evaporator. I am not an expert, but I think your low-side pressure should be closer to 30 PSI.

It would be most interesting to compare your system with another Foretravel of the same year and model to compare system configurations and operation.

Re: Dash A/C issues in a U280

Reply #22 – September 16, 2015, 05:40:53 pm

My condenser fans cut in and out with the compressor - maybe it's a Grand Villa thing. Every couple minutes doesn't sound unreasonable from what I've seen on my system.
When I converted to R134 I installed a dryer with a sight glass but have learned to charge it by measuring the output duct temperature. I use an electronic thermometer with a remote sense bulb so I can see the display through the front windshield. I slowly add R134 a bit at a time and note if it's improving the temperature drop or not. I stop when it seems to level off. As others have said too much will decrease the performance.
Sorry, I can't comment on if there is something else wrong - I've had little trouble with my system other than very slow leaks.
Hope this helps.

Re: Dash A/C issues in a U280

Reply #23 – September 20, 2015, 09:30:17 pm

Finally got around to working on the dash AC again today, hooked up the gauges and a temp probe on the refrigerant lines.
The temperature at the time was about 83
Low side pres was : 30
High side pres was : 195
condenser inlet temp : 138
condenser outlet temp : 107
evaporator inlet temp : 94.8
evaporator outlet temp 73.8
compressor inlet temp : 104
compressor outlet temp : 171

temperature inside the center vent : 71.8
temperature at the co-pilot floorboard : 77

Thank you Stump for all your help...

Re: Dash A/C issues in a U280

Reply #24 – September 21, 2015, 07:21:09 am

That tells me your subcooling at the condenserbus 21 degrees , were looking for 8 to 12 degrees,superheat at evaporator us 39.3 degrees we want around 10 tx valve regulates that so we look at subcooling to dial it in.
Evaporator is starved for refrigerant, condenser is starved add refrigerant.at 83 degrees gages should be 45-55 psi low side 225-250 high side thereabouts.you should see suction line leaving evaporatot start to condense water it will feel cold with your temp probe on condenser outlet and using your temp pressure chart I sent you take gage pressure and convert to temp on chart then subtract actual line temp that is your subcooling.shoot for 8-12 degrees superheat is checked the same way but with a tx valve it will be very consistent approx 10 degrees.add some more refrigerant and lets see what happens.

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