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PaulMears · 10-04-2018, 09:27 AM

2005 Gulfstream on 350 Cat Freightliner chassis.

While driving down the road, the AC starts blowing hot air. Sometimes it will go back to cold, then go back to hot. Sometimes it stays on hot. If it is delivering cool air when I shut down the RV and I leave the AC switch in the on position, sometimes it continues to blow cool air when I re start

It acts like the baffles are occasionally sticking in the heater position.

Since I bought the RV, 3 years ago, it has never blown "cold" air. I have had the AC checked and the tech says it is producing cold air.

I know there is an Evans flow valve, but don't understand how it works. Could this be the problem?

Suggestions?

nutcker · 10-04-2018, 02:05 PM

Yeah there is a valve that shuts off the water flow through the heater core when in the A/C mode. Its not uncommon for this valve to malfunction and cause the conditions you describe, most of us have installed a manual shut off valve in the heater hose going to the heater. This can be done pretty easy right near the heater housing in the front compartment, quarter turn valve cures the problem.

TonyMac · 10-04-2018, 03:05 PM

You're talking dash air? Sometimes these baffles are controlled by vacuum, and usually these systems default to defrost in the absence of vacuum. If your system is controlled by vacuum, then the problem is, you Cat doesn't produce vacuum like a gas engine, you have some other device to produce vacuum. Sometimes this device is engine driven, but I think in your case it is electrically driven and mounted on the forward side of the forward bulkhead, likely accessible when the genset is extended. Look to see if it's there, an electrical device about the size of a big coffee mug with a vacuum line coming out of it. The vacuum line could be damaged, but more likely the electrical connector is dirty and its connectivity is intermittent. When you lose electrical connectivity, you lose vacuum and the air conditioner turns to a defroster.

PaulMears · 10-04-2018, 09:44 PM

Thanks for your inputs. I will check the electrical connections on both devices.

Then I will look into the 1/4 turn valve or replacing the Evans valve.

Skip426 · 10-05-2018, 08:06 AM

If you only had the dash air switching between the vent position and defrost , that problem would be vacuum related; and possibly an issue with the 12 volt vacuum pump or a vacuum hose leak. Defrost is the dash system's default , no vacuum and you only get defrost air flow.
But with a temp change , you're more than likely looking at an electronic water flow valve ( Ranco ) issue .
I just replaced mine due to a coolant leak , and for my vintage of coach the part was a change up that required rewiring from the control panel to the valves location.
An inline manual shut off valve will help with the dash A/C operation , but if you have trouble maintaining heat while driving , you'll be looking at replacing the control valve.
Here's what my original valve looked like. Yellow circle, red circle is the 12 volt vacuum pump. Yellow X would be the spot to install a shut off valve.

PaulMears · 10-06-2018, 03:06 AM

Thanks. I will put a clamp on the line and see if the AC stays cold when the engine comes up to normal temp.

My systems normal operation is cold when the ambient air is cool and less cold when the ambient air is hot.

The blowing hot air problem has been an occasional thing. When the water flow valve goes, is it always malfunctioning or, in some cases, does it occasionally malfunction?

On one occasion, I could only get cool air out of the defrost. That may be a second problem.

RichKimball · 10-06-2018, 03:54 AM

Another that comes to mind is the condenser fan. It's not uncommon for these fans to fail and cause similar symptoms.
Check under the coach behind the gen set for the electric fan to see it it's running while the a/c is on. My bet is the fan has locked up.
They are easy to obtain at most auto parts stores for replacement.

PaulMears · 06-28-2019, 09:36 AM

I found the tubing to be hot both before the after the valve that stops the coolant flow when the AC is on, so I suspect the valve is the problem

When I cut the line to install a 1/4 turn valve, I will let air into the cooling system. Is this a problem, or do I need to vacuum the cooling system out and vacuum fill the overflow before running the engine

Thanks for your help.

Skip426 · 06-29-2019, 10:30 AM

Paul ,you'll probably be working above the height of the rad cap , so; remove the rad cap to make sure there's no pressure in the system , then re-install the rad cap. Next decide where you want to install your valve , if your access to the factory water valve looks like the photo I posted , I'd work there , get two sets of locking pliers and a couple of 2"x 5 " pieces of card board, fold the cardboard around the heater hose and clamp; the cardboard and hose; with the pliers , leaving enough room between to cut the hose and install the valve.
You'll probably only loose a quart of coolant and the air pocket will clear , top up the coolant after a drive with the new valve open and dash controls set to max heat.
Cardboard is there to keep the jaws of the pliers from cutting into the heater hose, and any hose in good condition will not be damaged by the pinching.

PaulMears · 07-18-2019, 04:54 PM

I had multiple issues.

First the CAC radiator was plugged completely. I don't know if this affects the air conditioner, but it is now clean.

Next, I put a quarter turn valve in the line going to the Evans Valve. With the heater on max, the line before and after the Evans valve was about 130 degrees.

With the AC on max, the line was still 130 degrees before and after the Evans valve.

With the 1/4 turn valve closed, the hose cooled quickly.

The air temp at the vent next to the drivers seat was 75 degrees with the 1/4 turn valve open and 53 degrees with the 1/4 turn valve closed.

I will still probably replace the Evans valve, because I want it right for the next owner. But, WEEEEEE pretty happy.

RichKimball · 07-22-2019, 07:11 AM

Very good...thanks for the follow up. A happy ending.

lonfu · 07-27-2019, 04:30 PM

I used one of these to replace the evans valve. new evans valve is a waste of money. the temp control knob only works adjusts the heat core valve to 3 positions. open, 1/2 open and closed. It has nothing to do with the AC temp. control. The heat valve opens when the mode is set to feet and dash vents...heat valve is open in all positions except AC and MAX AC and OFF.... The vent air door should be sealed shut, it will increase the production of both heat and cold......This new valve is normally closed, power applied then fully open. $38 is far cheaper than the evans $265.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

you can see the valve in the upper left corner.The cover was installed by a RV tech paid by the last owner.... you can see the gap where the pipes lead into the evap cover. I sealed around them. I now get 35 degrees at my center vent on ac. Heat and AC temps are controlled by the fan speed.

I chose to use my existing wiring harness. Most AC tech's will not install something like this for you because it is not factory and they are not engineers.