ENGINE A/C PROBLEM, NOT ALWAYS COOLING

To Doug's point about MAX A/C... Friends have an older, smaller, Class A. The refrigerant charge was low and we corrected that. They were still uncomfortable in the thing and I found that "normal A/C" allowed simply huge amounts of outside air into the coach. Not sure if it was design, install, or component failure but it was like trying to A/C with a window open. They now use the A/C on MAX. There are plenty of other ways to get some outside air into an RV.

Yes it could a Freon problem you could be over charged. Check that out or just keep on replacing parts then when you get done jumping this and that out. Correct charge is critical. Its a fairly easy system to diagnose.

What was the ambient air temperature,relative humidity and at what speed were you checking the output of the ac? The repair shop had a fan blowing air into your ac condensor, does your engine fan function properly? Under some circumstances, 62 degrees Fahrenheit is all that can be expected.

I believe they told me 2.5lbs of r134a was put into the system. They have the proper A/C unit to monitor the amount of r134a and system performance. System was only blowing approx. 62 degree cool air yesterday, so it seems either something is not letting the cold gas from the compressor reach the evaporator unit or as mexicowanderer says, the doors/gates are not cycling as they should.

Grave doubts your problem has ANYTHING to do with the freon part. A malperforming system can having the freon working overtime and duct inside or outside air directly through the dash vent ports.

1. I seriously doubt the output air was below 40 degrees. That mechanic either has a seriously un calibrated thermometer or he lied to you. You will NOT get below 40 degree air output on a class A motorhome unless the ambient temp was below 60 degrees.
2. Yes, you jump the 2 wires together on the 12 volt tstat freeze control to bypass.
3. The difference between MAX air and just AC on a motorhome is on MAX air the lower outside fresh air intake door is closed to allow recirculation of interior air which will result in colder output air. On just AC that lower door is opened and that allows hot ambient air to flow thru the Evaporator and will make getting colder temps harder.
4. The SPEC for Class A Dash AC systems is 60 degrees or below. But, almost all systems will get 55 or approach 50 degrees. When properly charged.
5. PROPER Charge is critical for a Dash AC system. TOO MUCH 134a and it will not cool correctly and will kick out the hi pressure switch. TOO LITTLE 134a, and it will not cool properly. Do you know how many OZ'S of 134a they installed? Your Ford requires either 2.25 lbs or no more than 2.75 lbs.
6. 134a systems, you CANNOT charge by the sight glass like Freon 12 systems. A fully charged 134a system will still show bubbles in the sight glass. You MUST install the exact charge to get optimum performance. The Evans/Tempcon Website will show the actual charge for your particular Ford chassis. Doug

TVX (assuming this is the expansion valve) was taped after installation. Front area of valve is exposed, but rest is wrapped. Tape was supplied with unit when it arrived.
We went on a trip earlier this year to TN and after stopping for lunch the A/C was noticeably warmer. Stayed in TN for a week and on the way home to VA it worked fine. This is whats so confusing. The repair shop had it working just fine and when I drove it home, the A/C was NOT blowing cold air (only cool air). We did NOT adjust the temperature setting, only switched the A/C to MAX and adjusted the fan speed to high. Never got cold.

Check for a misbehaving VACUUM control circuit misdirecting air ducting valves.

Class A's are very interesting in many ways. RV upfitter gets a chassis and installs what s/he likes, is available, is least expensive.
Point is, you probably do not have the HVAC system a Ford truck, van, auto would have. Doesn't mean it's bad, but does mean it's all the harder to troubleshoot especially remotely.

If your TXV was replaced, was the new one then wrapped in insulation, called Press Tite Tape? If not, it will sweat condensation. That condensation will frost, then freeze, covering the TXV in ice. Because of its design, the TXV will shut down, no more cooling.

It happened to us, on a "dealer air" system that used a TXV. Would quit cooling on hot humid days. I'd get out and chip the ice off. Then it'd cool again.

Did you just put a jumper between the two wires that are connected to the freeze sensor? I found the sensor and felt up to where the tube goes into the A/C box. Probe appears to be well down into the box. One of the A/C lines (metal fitting) next to the sensor was EXTREMELY COLD, so I know the compressor is working. Went through all of the settings on the control knob (vent-A/C, Max A/C, split dash/defrost and everything switched OK. Still confused why the COLD I felt on the fitting is not coming out the vent.
Found this unit at Comfort Aire and they call it a Cold Control unit and they sell for $36.97. I don't just want make sure I don't fry something by doing something stupid.