Dash AIR not working, blowing hot ! Not sure I fixed it??

[DAS26miles]

2015 Ford E450 V10
On return trip from the mountains, my dash air started putting out warm air. Clutch not engaging. I turned it off and checked the clutch fuse which was OK. When I got home, I jumped the connector at the accumulator and the clutch engaged and the air coming out of the vent was cold as normal.
This morning, I replaced the pressure switch with one from the Ford dealer. It was the exact replacement but I had to change the connector harness too. It's all installed per the instructions. Working fine, except, I noticed that it doesn't seem to cycle on and off at idle in my driveway and runs with the clutch engaged all the time. The ambient temperature is 90 degrees outside, would that have anything to do with it? The air coming out of the vents is 50 degrees and its 78 degrees in the motorhome. Ran for 20 minutes on Max with no cycling???

[DAS26miles]

Just ran outside and the ambient temp is down to 72 degrees. The lines are getting a little condensation and some frost on them and the temperature from the vent is still 40 degrees and I used another temp gun and got 28 to 35 degrees. I put the selector on normal instead of Max and lowered the fan speed. The clutch every minute or two disengaged for a bit and re engaged. So I think everything is fine and it was just a defective switch. As I mentioned earlier, it's just as cold as it was before.
Thanks to all for the information and possible reasons for the clutch being engaged all the time.

[STBRetired]

Temp gun is not the best thing for measuring air temp coming from vent, but a 28 degree temp difference is passable depending upon the humidity level. If the refrigerant (probably R134 not Freon) level was low enough that it would cycle the pressure switch you would not see that big a temperature drop. Quick and dirty check, grab the metal part of the line coming from the evaporator to the accumulator and see it it is cold. If it is, you are at least close to the correct charge. If it is warm, have someone put a gauge set on it and check the pressures.

[Cobra21]

j-d wrote:
This is only speculation. Any diagnosis without readings from an A/C gauge set is speculation.

First, Theory of Operation: The switch you replaced on Accumulator is a Low Pressure Cutoff (LPCO) switch. It releases your compressor clutch when Low Side (Suction) pressure falls below about 20-PSI. It does that for at least two reasons:
1. Pressure needs to be above around 20-PSI because the evaporator core temperature will fall below freezing.
2. Below around 20-PSI means the refrigerant charge is low. It may freeze the evaporator core, starting at a corner and working across, but only part of the core is cooling. Also, the compressor isn't being adequately cooled by returning refrigerant, and the lubricating oil may also not be circulating.



Speculation: Your system is just a tad below minimum charge level. At idle, compressor RPM and engine fan air flow aren't enough to pull the low side below 20-PSI. On the road, the compressor runs fast enough, and the condenser is cooled well enough, to pull below 20-PSI and the LPCO stops the compressor.

Please note: 20-PSI may not be the exact value. Looking at a low side A/C gauge, you can follow the R134A curve, and see what pressure causes temperature below 32*F. Low side pressure has to stay a few points higher than that.

I agree with Sunny's post. And I'll also add that the pressure switch you changed out was okay. Was just shutting down a system low on Freon.

[DAS26miles]

STBRetired wrote:
Could have just been a defective pressure switch, which you replaced. Drive it around for a few days and if it seems ok, then it probably is. If it was low on refrigerant, it would not be cooling on a 90 degree day. Thought the warrantee was 3 years, 36000 miles on Ford vehicles.

Thanks, that's what I'm hoping.

[STBRetired]

Could have just been a defective pressure switch, which you replaced. Drive it around for a few days and if it seems ok, then it probably is. If it was low on refrigerant, it would not be cooling on a 90 degree day. Thought the warrantee was 3 years, 36000 miles on Ford vehicles.

[DAS26miles]

Just turned blower speed down and temperature dropped at vent down to 40 degrees. Clutch does disengage when AC is turned off. Heat gun directed into vent went down to ZERO!. That makes no sense to me??????
Seems just as cold as in the past and everything appears to be working fine. Only 18 months old and 13,000 miles. Hate to have to take it in to Ford.
Will try again later when it cools down and will see if it cycles then.

[j-d]

This is only speculation. Any diagnosis without readings from an A/C gauge set is speculation.

First, Theory of Operation: The switch you replaced on Accumulator is a Low Pressure Cutoff (LPCO) switch. It releases your compressor clutch when Low Side (Suction) pressure falls below about 20-PSI. It does that for at least two reasons:
1. Pressure needs to be above around 20-PSI because the evaporator core temperature will fall below freezing.
2. Below around 20-PSI means the refrigerant charge is low. It may freeze the evaporator core, starting at a corner and working across, but only part of the core is cooling. Also, the compressor isn't being adequately cooled by returning refrigerant, and the lubricating oil may also not be circulating.

Speculation: Your system is just a tad below minimum charge level. At idle, compressor RPM and engine fan air flow aren't enough to pull the low side below 20-PSI. On the road, the compressor runs fast enough, and the condenser is cooled well enough, to pull below 20-PSI and the LPCO stops the compressor.

Please note: 20-PSI may not be the exact value. Looking at a low side A/C gauge, you can follow the R134A curve, and see what pressure causes temperature below 32*F. Low side pressure has to stay a few points higher than that.

[darsben1]

Sounds good to me.
I would not expect cycling on MAX.
Try running on normal and turning temp higher to see if it cycles

[DAS26miles]

Using a heat gun directed into vent shows 28 degrees. Why the difference? Ambient is 90 degrees.

[azdryheat]

I don't believe 50* is cold enough. I'd have it professionally checked.