Dash a/c?

[JimM68]

Our dash a/c (Evans) stopped getting cold. It all works, blows air and puts it in the right place, gets warm when I ask for heat, just don't get cold on a/c.

I verified that the water valve moves properly.

I crawled under and saw that the a/c compressor clutch never engages.

I bought a can of r143, but the system won't take any refrigerant (because the compressor clutch is not engaging?) The pressure gauge on the refill hose reads 150psi when it should be down around 40 (because the compressor clutch isn't engaging?)

Whenever I work on A/C systems, I always get stuck here... If I wait so long that the compressor isn't engaging I can't get it to take refrigerant.

What's the trick to get the compressor to click on so it will suck up the refrigerant?

[dougrainer]

mc.cc wrote:
The water valve can move properly and still be leaking. Just place a pair of vice grips on the water hose on either side of the valve and block the water completely. This will determine if the problem is the valve. Mine did the same thing. I went to Lowes and installed a hot water shut off valve on the other side of the factory valve. During the warm weather months I shut the valve completely off. During cold weather months I open it up.

Correct, but that will not cause the compressor to not come on. Doug

[mc_cc]

The water valve can move properly and still be leaking. Just place a pair of vice grips on the water hose on either side of the valve and block the water completely. This will determine if the problem is the valve. Mine did the same thing. I went to Lowes and installed a hot water shut off valve on the other side of the factory valve. During the warm weather months I shut the valve completely off. During cold weather months I open it up.

[Gjac]

Did you find the problem yet Jim?

[Kayteg1]

140 psi static pressure is way more than you need for compressor to start.
Usually low pressure switch is 30 psi.
You need to track why compressor clutch is not working. 12V check light and tracking the power from the switch will help.

[dougrainer]

gatorcq wrote:
the switch is on the dryer, and if it is low on freon it will shut it down. You really need to let freon into the system and see if it will kick in. Then your gauge will start working.

The switch can be on the dryer, but also on the line CLOSE to the Dryer. It will be up front at the evaporator area. You just jump both wires to get the compressor to come on. Now, you can add 134a, but the odds are it will be gone in less than a few days. You have a leak somewhere and probably NOT a small leak. But there is no harm in adding a few cans of 134a to determine how long the system will run before it leaks out again. IF you have both the HI and Low fill hoses connected, by opening the HI line to the 134a can, that will trip the low pressure switch to come on momentarily and you just keep opening and losing the HI side valve until it gets enough 134a to keep the switch closed to then fill the system full. Do you have an idea of howe much 134a to install? I always like to ask this question. 4 lbs is a full charge on a Roadmaster chassis with the Evanstempcon system. Doug

[gatorcq]

the switch is on the dryer, and if it is low on freon it will shut it down. You really need to let freon into the system and see if it will kick in. Then your gauge will start working.

[TNGW1500SE]

donn0128 wrote:
If the compressor wont engage, then your problem is not low of freon. Take it to a real AC service tech and have him fix it.

First statement is wrong.

Last statement is good advice!

Most any decent auto shop can charge it so you don't have to be gouged by the RV "techs".

[11178adm]

if you have 150 psi on the low side you have Freon. with the compressor running the pressure will drop. it sounds like a pressure switch or wiring problem, you may find the pressure switches at the front of the coach where the Freon lines go into the hvac unit they will be screwed into fittings made into the a/c lines they can be removed without losing Freon as there is a valve in the fitting on the line

good luck

[krivanj]

There are other reasons the compressor will not kick in. If it was working fine and then just quit, it could be pressure switches, thermostat, clutch relay, bad compressor or switch, or a fuse. I'd bet against low freon if it just stopped getting cold suddenly

[Gjac]

I have an Evans in a gas MH, so I don't know if it is set up the same way, but there is a switch either binary or trinity mine was a trinary switch and was leaking where the wires attach to the top of the switch. Once I changed the switch I was able to add 134 to the system and it has worked well for 5 years. You have to find the leak first before adding more 134. The switch should have 2 or 3 wires going to it.

[rgatijnet1]

There should be two wires coming off of the compressor. All you need to do is tap in to one of those wires with a needle type meter probe and feed in 12 volt power from any place that is convenient. You do not have to have the engine running to tell if you have picked the right wire. You will hear the compressor clutch engage and disengage. Once you know that you can energize the compressor, then you can start the engine and try adding freon. Make sure that you are doing all of this away from any fan or belts that could grab you and ruin your whole day.
Obviously this is not the preferred method of repair but it may get you through this crisis.
There may actually be only one wire, if they are using the compressor case for ground. In that case it is easy to pick the right one.

[JimM68]

I cannot get there. The compressor is high on the engine, I can barely see it. Certainly cannot reach it. Top access would involve removing the huge mirrored closet doors, emptying the closet, removing most of the t doorway trim, and finally being able to access and remove the hatch. Something I'd do if/when I decided to change the compressor, but not before.

Does anyone know for sure if the compressor is controlled directly by the dash controls and safety switches?
Or is it controlled by the ECM (like many newer cars are)?

This is an '08 Monaco entry pusher, cummins ISC, rear radiator.

would be really happy to lay some power to that clutch from somewhere outside the engine compartment.

[darsben]

JimM68 wrote:

donn0128 wrote:
If the compressor wont engage, then your problem is not low of freon. Take it to a real AC service tech and have him fix it.

All modern automotive A/C systems have a low pressure switch to prevent the compressor from eating itself running with no refrigerant. Just need to know where the switch is and jump it out. (I think)

Besides I have loads of reasons for fixing it myself, starting with "that's what I do" and then "I really don't have the spare cash right now to pay a shop to fix it" and finally "we are fulltimers, with 3 adults and 3 dogs living in this coach, currently camping in the middle of freeking nowhere"

Please note, people don't post on a help forum to hear "take it to a shop"

But thanks for your help.

The OP is correct about a low pressure switch. The control that you jumper should be right on the clutch with a couple of wires coming off it. Mine has a push on spade that I remove and put a 12 volt line onto. Clutch will engage. Make sure you are on the low side!!!

[JimM68]

donn0128 wrote:
If the compressor wont engage, then your problem is not low of freon. Take it to a real AC service tech and have him fix it.

All modern automotive A/C systems have a low pressure switch to prevent the compressor from eating itself running with no refrigerant. Just need to know where the switch is and jump it out. (I think)

Besides I have loads of reasons for fixing it myself, starting with "that's what I do" and then "I really don't have the spare cash right now to pay a shop to fix it" and finally "we are fulltimers, with 3 adults and 3 dogs living in this coach, currently camping in the middle of freeking nowhere"

Please note, people don't post on a help forum to hear "take it to a shop"

But thanks for your help.