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Old 08-17-2022, 07:40 PM   #1
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2002 W22 Chassis A/C

My monaco 2002 has a SCS A/C system. Clutch would not engage. Removed and meter checked Both fuses and installed new cmpr relay. I learned that low on 134 will shut everything off as I had no power to compressor. I bought a A/C pro extreme with digital gage lol. I hooked up the quick disconnect started motor and turned a/c to max had 6 psi on the gage. Squezzed trigger and pressure went up a little but I heard a hiss behind alll the rubber baffling. Stoped checked pressure Added more several times hissing finally stopped gage wet to 26 and clutch kicked in fans spun for maybe 2 seconds. Pressure went down but not as far. Continued this process the most 4 maybe 5 secs. on off on off pressure was 18 when I finally stopped. shut engine off Still no cold. Turned gage back on (motor off and it read 62 PSI ,What the hell. Is there a bleeder valve that must be open when adding 134. We are leaving on saturday.What do I need to do to keep that compressor clutch engaged?
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Old 08-17-2022, 08:22 PM   #2
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My recent trials and tribulations on an ‘02 chassis using an Evans unit (not much different from and SCS).

https://www.irv2.com/forums/f258/eva...on-589542.html

If ou coach has th king valve at the evaporator, you have to remove the cap off of the stem and cracking it open about 1/4 turn. Then you can add refrigerant.

The Delphi compressors GM used in that era had a design flaw that they would leak. Hard to see without removing the compressor.

I’ve documented that issue on this site as well - just don’t recall if. Did so in the referenced thread.
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Old 08-17-2022, 08:38 PM   #3
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Quote:
Originally Posted by fayjim2 View Post
We are leaving on saturday.What do I need to do to keep that compressor clutch engaged?
Take it to a professional. It's not worth messing with yourself unless you have the right gauges and know what you are doing.
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Old 08-17-2022, 08:43 PM   #4
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The 62psi is the static pressure when the high side and low side equalize with the system off.
The 18psi is your low side pressure, which is where you charge. Around 30psi is good.
Sounds like you need more 134.

A vacuum pump to pull it down to check for leaks and to pull out any moisture and a full set of gauges are really the way to go.
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Old 08-17-2022, 09:30 PM   #5
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So.. it's hail Mary time.. you have no time for shop.. you have no time to grab book on basic automotive air conditioning repair book.. they are online or every auto parts store.. which should be in rv library by now..
So yes.. when compressor is running.. on the low side of a/c hose connection.. it's sucking Freon it.. as gas.. and it uses power from engine to turn gas to liquid.. so never fill on hi side connection.. that is why they are different fitting..
So when you stopped compressor.. the liquid equalize and the pressure on hi side goes up.. now you need a book for this.. but I am going to give you brief description..
Keep can up.. yes it's slow.. start engine and a/c.. disregard first hi reading.. unless over 200 psi.. add Freon.. until about 40 to 45psi.. may take 2 cans..
Anything over that you probably have big leak.. get book it will tell you how to deal with that..
Now the hissing could be big leak.. that you will have to sort out when you come back..
The hiss could be normal.. you see.. there is a orifice tube.. called expansion valve.. inside a/c box.. that turns liquid to gas.. when that happens you get cooling..
So.. if his is inside a/c box.. behind rubber air dam.. it could be normal.. but.. maybe not.. so if hissing from big hoses you can see or from compressor.. you will just have to deal with that when you get home..

So if hissing in box.. keep running and filling.. as you put more in.. the pressure will go up.. if not.. then stop.. and deal with when home..
If pressure slowly goes up.. get your free hand on large hose.. it will be cold because you are adding gas.. then carefully put on small a/c hose.. hi side.. it should be very hot..
If pressure going up.. stop about 30 to 35psi.. by this time compressor should stay engaged .. stop filling.. watch pressure..if it stabilizes and remains constant..look under front.. at a/c box.. there is a drip hole.. water should be coming out of it..
It's making water.. good.. pressure good.. now get someone to get engine rpms. To 1200 to 1500.. just off idle.. and watch low side pressure drop.. good.. now fill with can 2.. and try y o get as close yo 40.. as you can.. if you try more than 3 cans.. could be a problem.. should only use 1 to 2.. just under 2cans would be great.. disconnect filler hose.. replace cap.. see if cold inside.. now I left out a lot..use all safety precautions.. and stop if you feel un safe..
Good luck and keep us posted
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Old 08-18-2022, 06:57 AM   #6
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Good advice so far but it is incomplete. Modern automotive refrigerant is R134a. Its characteristics are significantly different from the old refrigerant R12 that was used until the mid 1990's.

The appropriate pressures for R134a is variable with ambient temperature. See the attached chart. Once there is enough refrigerant to close the low pressure switch keep adding R13a until you attain the pressures shown on the chart.

I recently charged my dash air. It was 90° outside so I set the low pressure side at 50 PSI. I was lazy and didn't check the high pressure side.

As of 2021 R134a is being phased out. There are several candidates for its replacement the most prominent is R-1234yf.

The internet has mixed messages of whether the new refrigerants are compatible with R134a systems!
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Old 08-18-2022, 07:56 AM   #7
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Donr103 A/C

Its early but I still need to no about the hissing. It sounds at the compressor,but like I said that stopped. But why the cycling on and off every couple seconds. Does the compressor have to be engaged to allow the can of coolant to enter system? I,m sure I need to add more 134 after reading the posts. I never done that stuff before, but I would like to learn. Thanks for help so far. Jim
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Old 08-18-2022, 08:29 AM   #8
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Its early but I still need to no about the hissing. It sounds at the compressor,but like I said that stopped. But why the cycling on and off every couple seconds. Does the compressor have to be engaged to allow the can of coolant to enter system? I,m sure I need to add more 134 after reading the posts. I never done that stuff before, but I would like to learn. Thanks for help so far. Jim
You have to be patient. It takes a long time for the R134a to go from the can to the AC system. The compressor cycling may become less as the amount of R134a in the system increases.

At least get a low pressure gauge. Many R134a cans come with a gauge. Fill the system according to the chart. As the system fills it takes longer for the R134a to go from the can to the AC system.

Run the engine ~2000 RPM while filling.
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Old 08-18-2022, 08:55 AM   #9
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In layman’s terms…

There has to be a certain amount of Freon (pressure) in the system in order for the compressor to kick on. Don’t recall the number, 10psi??? Once the compressor kicks on, it will cycle off/on with a low psi. Once the psi is high enough, it will stay on. Then charge to the recommended psi. There is a pressure switch on the line that detects the psi. It prevents the compressor from coming on and destroying itself with no Freon/oil.
Many will just add an oz if the system has been empty hoping, or actually guessing, that’ll be good enough.
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Old 08-18-2022, 02:47 PM   #10
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A/C

Is the highrer rpm necessary after there is sufficent low pressure to keep clutch engaged or higher rpm from the start of filling the 134?
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Old 08-18-2022, 03:42 PM   #11
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Higher rpm is needed to move air across condenser and radiator.

Mostly needed for condenser to get head pressure down, better condense refrigerant as system was designed to be going down the road.
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Old 08-18-2022, 04:47 PM   #12
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So.. at 1st.. yes compressor must be running to circulate Freon in system.. Freon will flow from can into system.. and then a sensor starts compressor when engine running.. again you need to educate yourself and get several books.. understand you need to get on road.. so real brief..
TOO ALL ORTHER MEMBERS .. I am not here to give op and 9 months course of a/c repair..
2nd question.. you need someone to hold rpms around 1200 to 1500 rpms.. 2000 rpms is too fast in my humble opinion.. why.. because the system is designed to pump Freon through system at that rate.. you will get many opinions and there are many ways to do things.. but you said you are leaving this weekend..
Good luck and keep us posted
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Old 08-18-2022, 05:13 PM   #13
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Go to the Files section of this board, then to “chassis”. Type in “Evans” as a search term.

There is one guide there that will a sewer many of your questions in about 10 pages.
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Old 08-18-2022, 05:21 PM   #14
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So.. at 1st.. yes compressor must be running to circulate Freon in system.. Freon will flow from can into system.. and then a sensor starts compressor when engine running.. again you need to educate yourself and get several books.. understand you need to get on road.. so real brief..
TOO ALL ORTHER MEMBERS .. I am not here to give op and 9 months course of a/c repair..
2nd question.. you need someone to hold rpms around 1200 to 1500 rpms.. 2000 rpms is too fast in my humble opinion.. why.. because the system is designed to pump Freon through system at that rate.. you will get many opinions and there are many ways to do things.. but you said you are leaving this weekend..
Good luck and keep us posted
My 8.1L GM engine turns ~2200 RPM at 60 in overdrive. I think the 6 Speed Allison versions are about the same RPM at 60 in 6th. I think ~2200 RPM might be the operating RPM for a gasoline Workhorse chassis!

The OP says he has a 2002 Workhorse W22. That means he has an 8.1L GM engine and an Allison 1000M 5 spd transmission. Regardless of stock tire size the stock matching differential gear will set his 60 MPH RPM at ~ 2200.

I would fill at ~2000 RPM. It ain't critical but being close does matter.

Just sayin'
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