Coach A/C Compressor won't engage

[Bill C]

Good Day, and thank you for taking the time to review my issue.

I can't get my coach A/C compressor to engage (dash set to MAX A/C). I could not find any fuses in the outside fuse panel below the driver’s seat.

In the engine compartment I found a reset-a-ble fuse OK and replaced the relay, just in case (both are labeled A/C clutch).

I'm not sure where else to look at the moment. I checked the freon, added one can, and with the filling cord trigger released, it reads green, indicating it has enough freon. I hate to add any more, in an attempt to get the compressor to engage, for fear of over filling it with freon.

I looked at the compressor for wiring and only found one wire going to it. Is this normal (here is a pic). Should I read ground or 12v at this wire?

Any help would be appreciated as we live in FL and the warm season has started.

Thanks,

Bill

USN Retired

 

[timaz996]

My dash switch is dirty and sometimes I have to click it back and forth from vent to Max A/C a couple times and it works. One day I'm sure I will have to clean it.

 

Tim

[vito.a]

Most of these systems hold four pounds, so one 12 ounce can is not going to fill it enough for the compressor to kick in.  Our coaches are getting old with over 40 feet of A/C hose from front to back so they tend to seep down when they sit.  

You really need a set of gauges (even inexpensive Harbor Freight).  The dryer should be replaced first.  My dryer was around $25.  The dryer is up front in the generator compartment.

Then pump the system down to a vacuum and service with the proper amount of R410.   There are many YouTube videos on servicing AC systems but my recommendation is to find a friend that can help you.  

[Bill C]

I did replace my dash plate this last year had to disconnect the wires to the AC controller. But I have double checked and triple checked them and wiggled them since this problem started so I don’t think it’s the dash control. I do have a set of gauges if somebody could tell me what they should read when it’s normal that would sure be appreciated. I’m not a AC expert just a hacker

[timaz996]

Go on YouTube and find a video on how to charge your car A/C

 

Tim

[Ivan K]

I will assume that since your simple gauge shows green, there is at least enough pressure to close low pressure switch. But since you mentioned to have gauges and the clutch does not lock, both ports should read the same, depending on ambient temperature but certainly more than 30 or so psi to close the switch. If so, you have an electrical issue and need to trace the 12v positive all the way from the fuse or breaker, through the dash dial and pressure switch (might even have a high pressure switch) to your single clutch wire.

Once the clutch works, here is a simple pressure chart for R134a.

[Specialk]

My suggestion would be to rule out the electrical issue at the a/c clutch first.  From the picture it appears that the compressor clutch is grounded at the Phillips screw terminal and therefore the wire that has the butt terminal splice would be your “DC” source for power.   Take the wire loose from this butt connection and check to see if you have power there when you cycle the A/C.  If not, I would leave the wire disconnected and then take a known good 12volt source and with the engine “NOT” running apply 12volt momentarily to the clutch wire.  If it engages, then begin tracing out the wire to the source.   Since you have already added Freon, (It doesn’t take much Freon pressure to engage the clutch),I would not add additional Freon until you can cycle clutch.   Low Freon (not no Freon)  will simply cycle on/off quickly, due to low pressure developing quickly when clutch engages.   Once clutch engages then the gauges will become useful to determine the status charge.   Hope this helps

[Cubflyer]

4 minutes ago, Specialk said:

My suggestion would be to rule out the electrical issue at the a/c clutch first.  From the picture it appears that the compressor clutch is grounded at the Phillips screw terminal and therefore the wire that has the butt terminal splice would be your “DC” source for power.   Take the wire loose from this butt connection and check to see if you have power there when you cycle the A/C.  If not, I would leave the wire disconnected and then take a known good 12volt source and with the engine “NOT” running apply 12volt momentarily to the clutch wire.  If it engages, then begin tracing out the wire to the source.   Since you have already added Freon, (It doesn’t take much Freon pressure to engage the clutch),I would not add additional Freon until you can cycle clutch.   Low Freon (not no Freon)  will simply cycle on/off quickly, due to low pressure developing quickly when clutch engages.   Once clutch engages then the gauges will become useful to determine the status charge.   Hope this helps

Adding to this, I had the same problem last summer, no compressor engagement... did what Kevin said, (assured the clutch on the compressor worked) then traced the problem to a switch/sensor up front (by the generator) on the freon lines .... jumpered that and the compressor engaged... I believe it is a 'low freon pressure switch'.... there must have been bad connections there as after 'playing' with the connections the system operated normally....

Ken

[MrAmbassador]

My problem was the thermostatic switch found to the left in the front generator compartment. The switch is normally closed and allows clutch engagement. When the evaporator gets to cold the thermostatic switch opens and shuts off the compressor or disengages the clutch. Disconnect the thermostatic switch wire and place a blade fuse in its place, now check and see if the compressor engages. If it does you need to change out the Thermostatic switch. Don’t run the compressor for too long with the blade fuse because you can damage the compressor since it does not cycle. Hope this helps. 

[Bill C]

I’ve seen a couple suggestions of places to look. Would anybody happen to have a picture of what I’m looking for?

[jacwjames]

Check the Downloads

There are several files in the folder for the AC systems for Dash HVAC

[trailmug]

I'm with Ivan on the suspect pressure switch.. jumper the pressure switch terminals (usually up front near the receiver) and see if the compressor engages. Those binary switches are pieces of crap. Don't run it that way for long, though, just enough to verify. Low refrigerant would mean low oil circulation. 

[MrAmbassador]

Here is a drawing:

[trailmug]

I would also add that if the system took a can of refrigerant while the compressor was not running, it has a major leak and was empty. If the system had liquid, and the can had liquid, and both were at ambient temperature, there would be essentially no flow of refrigerant from the can because they'd be at the same pressure. 

Edited March 30, 2022 by trailmug

[Ivan K]

3 hours ago, Corkman said:

I’ve seen a couple suggestions of places to look. Would anybody happen to have a picture of what I’m looking for?

Here is what the pressure switch would likely look like. Mine is beside the genny. Should be positive on at least one lead. You can pull the connectors and jump them with a fuse for test. Rob raised a good point, you would not be able to charge it from a can if the system already had a good static pressure, same as in the can and you can't overfill it that way while not running.

[Scotty Hutto]

18 hours ago, vito.a said:

…Then pump the system down to a vacuum and service with the proper amount of R410. 

Minor correction… and double check your system to be sure… I believe most dash ACs of 2001 vintage should be R134a. 

R410a is typically used in the Dometic Penguin (rooftop) units.

Otherwise Vito’s advice is spot on!

[vito.a]

Scotty's correct.  Mind slip.  

[cbr046]

My dash AC worked on the way to my destination Friday but not the way home Sunday.  Got tired of running the generator so pulled into a Lowe's 200 miles from home to add a can or two of refrigerant.  With the AC on max I had 110 psi on both hi and low sides (static).  The compressor wasn't running . . . . but why? 

Got to it today and able to read up, open the rear hatch, watch the compressor, short the pressure switch and add 36 oz of R134A (yeah, a lot!).  Final pressure settings were 30 low / 150 high with 55F at the louvers.  Ambient was 80F. 

The biggest question is whether the low pressure switch is going bad or was it just a case of low freon?

Got another trip this weekend . . . .

- bob

 

 

[Cubflyer]

Adding the freon seems to have brought your system back operational.  Last summer I thought my dash system was low on freon but found it was not. My problem was the thermo switch that turns the compressor off when the evaporator temp gets to about 32 degrees and would start to ice over.  It's a little metal box with a small tube like temp probe coming out of it that goes into the evaporator case (up front near the pressure switch, I believe they are wired in series). Inside the box is a micro switch that is normally closed, opens when sensing about 35 degrees. Replacing that brought my system back into cold ops until this afternoon on the way back from Ohio... right now my a/c is running but the air is cool, not cold.... going to have to check it out tomorrow.  

[TimSpencer]

9 hours ago, cbr046 said:

My dash AC worked on the way to my destination Friday but not the way home Sunday.  Got tired of running the generator so pulled into a Lowe's 200 miles from home to add a can or two of refrigerant.  With the AC on max I had 110 psi on both hi and low sides (static).  The compressor wasn't running . . . . but why? 

Got to it today and able to read up, open the rear hatch, watch the compressor, short the pressure switch and add 36 oz of R134A (yeah, a lot!).  Final pressure settings were 30 low / 150 high with 55F at the louvers.  Ambient was 80F. 

The biggest question is whether the low pressure switch is going bad or was it just a case of low freon?

Got another trip this weekend . . . .

- bob

 

 

If you have 110# and you jump low pressure switch, it’s a bad switch. 

[cbr046]

57 minutes ago, TimSpencer said:

If you have 110# and you jump low pressure switch, it’s a bad switch. 

Thanks.  It's working now, probably because I was fiddling with it, but that doesn't mean it won't fail again in the near future.  Good thing winter is coming. 

- bob

[trailmug]

My money's on there's a leak and the switch is sticky. I expect spring will find you in the same situation, but you've got a head start on it. 🙂