Dash AC

Topic: Dash AC (Read 1404 times) previous topic - next topic

Dash AC

April 30, 2013, 08:57:44 pm

Well, I had the resettable breaker replaced when I had my condenser fan replaced. The fan was bad and the AC would stop with high pressure. Now on the trip home the AC quit again. I could not figure this one out. I looked at the breaker and that had 12 volts. Put 12 volts to the AC and it turned but it did not turn. I had a switch replaced too but that showed it went on up front. I was at a loss so I was driving by my Cummins on I 81 and pulled in. I asked them if they could look at it for me. They took me right in and had be back into the bay they do speedy oil changes on. The tech came over and i showed him what I had done but he wanted to repeat a couple of things so he could do it in the order to help him figure it out. He came and asked about other fuses or relays. I was stumped so I showed him the ones under the bed. Sure enough it was the 12v 20-30 amp tyco relay. They had one and put it on. 16 dollars for the part 279 inlabor to find what to change and 48 degree ac now. They are the square relays under the bed next to the resettable breakers. I will be changing out the others as this one was corroded.

Re: Dash AC

Reply #1 – April 30, 2013, 10:35:47 pm

As long as we are on this topic, I will ask my question here.

My dash AC was not working very well this spring so when I took it into the Freightliner service center here in Tucson for an oil change, I had them look at it. They saw some "oil" residue around the hi side port and on a connection near the condenser. Based on this "evidence," they wanted to start replacing hoses, including the ones to the front of the coach. At that point I told them to stop. Oh, and then managed to loose the high side inlet cap, but that is another story. And they charged $100 for all of this!

Last year I had the system charged with 3.5 lbs of 134a which contained fluorescent dye. At that time, the tech also replaced the Schrader valves in the ports. I bought a black light and could find no evidence of recent leaks around the fittings that Freightliner thought were leaking. So a friend helped me add a 12 oz can of Walmart 134a. It is now blowing 47 degrees from the dash (outside temp 85). I also bought some AC gauges and got the readings shown with the engine at idle and the AC on max and dash air blower on max.

My question is, what should these gauges read if the system has enough 134a?

Thanks in advance

Re: Dash AC

Reply #2 – April 30, 2013, 10:56:51 pm

We have similar problem , dealer charged system , no leaks but still not blowing cold .
Will report back thier findings

Re: Dash AC

Reply #3 – April 30, 2013, 11:40:19 pm

George,
I got these limits from a general automotive A/C book I have. I put a label on the gauges so the information is right where I need it (limits are in PSI).
These limits are a general guide. I like to use the sight glass and add 134A just until all the bubbles are gone (applies only when compressor is running). Not all systems will have a sight glass - if it does it will likely be at the top of the dryer. Looking at your gauges in your post, I'd say you need more 134A.

Often the gauge readings will be off on one side or the other. I think the following affects the readings:
outside air temp
engine idle speed
inside blower speed
if the condenser fan is running or not
if the compressor running or not

The book is handy in that is shows gauge readings for various failure modes.

Re: Dash AC

Reply #4 – May 01, 2013, 07:48:46 am

Check your condenser fan. That seems to be the culprit a lot of the time. I have replaced that on three different FT now. IT is behind the rear wheels and seems to go out every so often. Also see if your compressor is turning. If it is not that is a different problem then RF 134. If it is turning then you must have a leak somewhere. I put the dye in too and found three leaks about two years ago now. IT has been working till the condenser fan died. Then the relay failed. I have also had to replace the high pressure switch too. All of those seem to cover just about everything.

Re: Dash AC

Reply #5 – May 01, 2013, 08:24:03 pm

John.... did you check the front end connections of the dash AC system and if so, how did you get to them? Any pics?

George

P.S. Thanks for the tips!

Re: Dash AC

Reply #6 – May 01, 2013, 08:34:47 pm

George,
The 97 dash is different from yours, but I believe the same principle applies. That is, the dash has to be diassembled to get at the expansion valve and the evaporator.

Re: Dash AC

Reply #7 – May 01, 2013, 09:44:45 pm

To get the correct amount of R134a you need to calculate superheat and subcooling. This will require a clip on thermometer to measure the freon line temperatures. You can get close with just pressures but performance is significantly better when done properly.

Re: Dash AC

Reply #8 – May 01, 2013, 09:52:25 pm

Quote from: sedelange – May 01, 2013, 09:44:45 pm

To get the correct amount of R134a you need to calculate superheat and subcooling.

That's a fact, and it's something that very few AC techs take the time to do. I built a new house with six tons of high eff air, new owners were unhappy with AC performance, I thought I was going to have to upsize the systems. All it took to fix it was a different contractor who measured line temps, outside temps, return air temps as I recall and calculated proper charge. The cooling went from marginal to excellent, it was like the tonnage was increased, happy homeowners and one relieved builder. This was a cap tube system rather than expansion valve as on the coach.

Re: Dash AC

Reply #9 – May 01, 2013, 10:22:16 pm

Okay Steve,

How do you calculate superheating and subcooling?

Do you have a picture and source for clip on thermometer?

Thanks,

Re: Dash AC

Reply #10 – May 01, 2013, 10:38:08 pm

Can one use an IR (point and shoot) thermometer?

George

Re: Dash AC

Reply #11 – May 01, 2013, 11:08:54 pm

You can. I don't think it's as accurate and it is really hard to hit the freon lines at the evaporator. I was able to borrow one so I was lucky. BTW, if you service a R134a system until the sight glass is clear, you are usually overcharged.

Re: Dash AC

Reply #12 – May 02, 2013, 11:47:46 am

A couple of years ago I used a very rudimentary gauge to fill my AC with 134A and it didn't improve things at all. I then took it to Foretravel and the found it was over charged by about 20%. They corrected the the Freon level and it started working great again. Over filling can be as bad as under filled.

The AC units in the Grand Villas normally work very well. We seldom ever use the roof air conditioning when traveling, even in 100 degree plus weather.

Re: Dash AC

Reply #13 – May 02, 2013, 11:56:06 am

Anyone know the exact qty of r134a that should be in my 97 u320 40'?

Both my car and truck were incorrect and now fixed. And work much better.

Re: Dash AC

Reply #14 – May 02, 2013, 12:06:39 pm

When I recharged my dash air three years ago, I had the help of a trained refer tech.
I put a thermometer in a dash output grill and he added one can of 134a at a time, waiting between cans (took about 6 cans). When dash output air temperature dropped he stopped adding 134a.
Dash A/C worked for 2 years, then quit. I added one can at a time until cold air from dash vents. Still works today, although I wonder if it is working at 100%.

Re: Dash AC

Reply #15 – May 02, 2013, 01:46:09 pm

When I serviced my 96 U320 it was supposed to be 5lbs. We put in 4.5lbs (90%) then turned unit on and let it stabilize while watching all the temps. Tweaking brought it real close to 5lbs. Possibly 5.2

Re: Dash AC

Reply #16 – May 02, 2013, 02:07:54 pm

I have used the following two Web forums in the past and found their information to be quite valuable.

Automotive Air Conditioning Bulletin Board • Index page

Automotive AC Information Forum - ACKITS.COM

One of the moderators on the acsource.net forums goes by "Nacho" and runs a shop in Mexico. He has been most helpful in answering my questions and providing information. (As a bonus, his English is far better than my Spanish!)

As has been mentioned, overfilling (particularly HFC-134a) will cause degraded performance, and filling a 134a system to the point where there are no bubbles visible in the sight glass typically means that the system has been overfilled.

Re: Dash AC

Reply #17 – May 02, 2013, 03:56:44 pm

Quote from: sedelange – May 02, 2013, 01:46:09 pm

When I serviced my 96 U320 it was supposed to be 5lbs. We put in 4.5lbs (90%) then turned unit on and let it stabilize while watching all the temps. Tweaking brought it real close to 5lbs. Possibly 5.2

Does it make a difference on the amount or R134a needed that a coach is 40' as opposed to 34'? I think Forrest require 4.5 Lbs.

Re: Dash AC

Reply #18 – May 02, 2013, 04:08:26 pm

Like products for radiator leaks, there are some for AC system leaks. For example....

R-134a Super Seal A/C Leak Sealer by Interdyamics : Amazon.com : Automotive

Has anyone used one of these? Effective? Problems?

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

Re: Dash AC

Reply #19 – May 02, 2013, 05:21:14 pm

I took it to Thermo king when it was broken before. Cummins referred me to them as they could fix it and charge it back up. This time it was a switch or relay as it was working and would not turn on until I put 12 volts to it myself. So, that told me it was a switch so Cummins could crawl around and find it. I would think that the different length coaches have different amounts if for nothing else then longer lines to run the stuff thru.

Re: Dash AC

Reply #20 – May 02, 2013, 06:36:15 pm

Quote from: Peter & Beth – May 02, 2013, 03:56:44 pm

Does it make a difference on the amount or R134a needed that a coach is 40' as opposed to 34'? I think Forrest require 4.5 Lbs.

The length of the lines does make a difference. There is a rule of thumb (which I don't recall right now) for how to add or subtract (the proper amount of charge) based upon line length. However, it seems the best way to ensure an existing system has the proper charge is to use the gauges and a thermometer and to stop one the optimum cooling appears to have been reached.

Re: Dash AC

Reply #21 – May 20, 2013, 08:14:47 pm

Our dash AC problem finally seems to be fixed....blowing about 35 degrees below ambient. We are in Santa Fe, NM and took the coach to Hal Burns Truck and Equipment (Hal Burns Truck and Equipment - Santa Fe). The tech (Bill) found that the high pressure hose was leaking at the crimps on both the compressor and condenser ends. Dye had been added to the system last year, but it was not until he evacuated and removed the 134a from the system that he found the leak by pressurizing the system with compressed air. He used a soap solution to find the leak. Evidently not enough dye was used which is not surprising given the volume of the AC lines. Removal of the hose (which must be about 10' long) was not easy since it runs to the back of the engine, over the transmission and then to the condenser which is next to the muffler. There must have been 20 wire ties holding it in place. Once removed, the fittings were replaced by a local shop and and system was again evacuated. Then the 3.5 lbs of 134a was replaced.

I also had him check for a possible leak in the engine cooling system. The coolant in the overflow reservoir has been slowly dropping over the last year. He found a loose (and leaking) plug on the back of the engine head. Another problem solved.

Then I had him remove 2 quarts of excess oil that Freightliner of Arizona (Tucson) had added when I had the oil changed earlier this year. Why is it such a problem to add the right amount of oil?

This was our second visit to Hal Burns and I cannot say enough about their great services. I especially appreciated Bill's willingness to answer my questions. Just a great place to get service!

Re: Dash AC

Reply #22 – May 23, 2013, 10:24:17 pm

that was the same hose that I had replaced on my 03 u320

Re: Dash AC

Reply #23 – June 05, 2013, 04:54:37 pm

New compressor $1200 , dealer paid major share . Thanks for al the advice

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