Any air conditioner experts out there? My dash air was operating just fine until a couple of days ago. Here's the deal. I start the rig and turn on the dash air. I can hear the compressor pull the engine down just a bit like usual. Soon, the air blowing from the vents begins to cool. Gets down to the high 50s (85 or 90 outside) and then cooling stops and the air warms. I watched the compressor and see it run at startup, however, after five or ten minutes the compressor starts cycling on and off, mostly off. It will run for 5 seconds, shut down for 45 seconds to a minute, run for 5 seconds and so on. The condensor fans are up front and I see they are running. I don't have gauges but I do have a can of 134a and one of those cheapy hose/gauge deals. I hooked it up to the low pressure side and see around 40 when the compressor is running. Then it jumps way up to 90 or so when the compressor quits, back down when it starts and so onlI need to take the rig in to check a brake and wheel bearing and I'll have them take a look at the A/C too. Anyone have an idea of what's going on? Thanks.jor

Short cycling is an indication it could be low on charge. But you really need to fix the leak before re-charging it.

On a 95 Foretravel I would not worry about a leak if this is the first time in 4-5 years. Add 1/2 a can of 134 and see if it stops cycling. I use a IR temp gun on the condenser coils to see when 90% of them are hotter than the last one to judge how much more freon to put in. One can should be more than enough so do it yourself for $15 or have them do it for $100.

First Take a look under the front of the RVFind the evaporator and the big 12v fan, looks like trans coolerMake sure that fan is running2 yrs ago mine died and I had exactly the same symptoms, IWhen checking and testing I found the fan 25 amp fuse was bad, replacement blew as soon as I turned on the A/CReplaced the fan with new one from AutoZone, take the old one in when shopping for new one

If you have no airflow over the condenser like a bad fan or blocked by plastic bag or something, it could kick off due to high side pressure cutoff.Most likely its the low side pressure switch due to low charge or bad switch.....I had one fail once.This is all assuming you have a CCOT type.....cycling clutch orifice tube and not an expansion valve type.

MrWizard wrote:First Take a look under the front of the RVFind the evaporator and the big 12v fan, looks like trans coolerMake sure that fan is running2 yrs ago mine died and I had exactly the same symptoms, IWhen checking and testing I found the fan 25 amp fuse was bad, replacement blew as soon as I turned on the A/CReplaced the fan with new one from AutoZone, take the old one in when shopping for new oneCondensor, NOT Evaporator. The OP states he has checked and it is running. Doug

Cycling A/C Compressor | Good Sam Community

26 Replies

joraz
Explorer
Jun 04, 2014
Thanks, Doug. I got the 43 degree figure with my digital thermometer pointing directly at the dash vents. I would get that figure consistently. The correct pound charge is 5# for sure. Anyhow, when I head down there later today, with your figures in mind, I'll find out what the tech considered too high. BTW, when I dropped it off the condensor fans were working fine. Thanks.
jor
dougrainer
Nomad
Jun 04, 2014
joraz wrote:
OP here. After adding a can with no change I took the rig to a shop. They found a leaking compressor and a bad expansion valve. They replaced the compressor, expansion valve and dryer. They also found contaminants so they flushed the entire system. They just called me to advise that it's done. Anyhow, the service guy advised me:
* that it's blowing at about 53 degrees. This is 10 degrees warmer than what I had before it let me down a few weeks back.
* that they were only able to fill with 3# because the pressure was getting too high. According to my documentation, this is a 5# system.

I don't know what pressures are appropriate. The ambient temp here is about 100 degrees. I'm nervous that this thing will not be fixed right!
jor

I doubt you had 43 degree output at 90 plus temps. Very FEW Class A's get that temp when over 80 degrees ambient. The "norm" is anything below 60 degrees but MOST will get below 55 degrees. Having a full set of gauges would have shown the expansion valve bad. IF your documentation has a sticker that shows 5 lbs of coolant, then IF the pressure did indeed get too "high", then I would suspect the condenser fan system was not functioning correctly. But if it states 5 lbs and they only put 3 in, then it is NOT fully charged. But it depends on what they think is too "high". Ask what that hi pressure was. The hi pressure depending on the ambient will be from 175 to 275(95 degrees)psi. I would call Foretravel with your year and VIN and ask them the correct Lb charge. That will verify if the sticker is correct. Doug
joraz
Explorer
Jun 04, 2014
OP here. After adding a can with no change I took the rig to a shop. They found a leaking compressor and a bad expansion valve. They replaced the compressor, expansion valve and dryer. They also found contaminants so they flushed the entire system. They just called me to advise that it's done. Anyhow, the service guy advised me:
* that it's blowing at about 53 degrees. This is 10 degrees warmer than what I had before it let me down a few weeks back.
* that they were only able to fill with 3# because the pressure was getting too high. According to my documentation, this is a 5# system.

I don't know what pressures are appropriate. The ambient temp here is about 100 degrees. I'm nervous that this thing will not be fixed right!
jor
joraz
Explorer
May 27, 2014
The compressor cycle time is just what you would see from a low charge and the hi pressure switch kicking in and out. Doug

I'll add a can tomorrow and see what happens. It is a 134a system. I was afraid of overcharging it. Re the high pressure switch and fuse, I'll check with my rig specific discussion group and get back. Thanks for your help.
jor
joraz
Explorer
May 26, 2014
Hmmm... My rig has two 30a auto reset circuit breakers behind the dash. These control the A/C fan and A/C evap blower. In the rear it has an A/C relay and a 15a auto reset circuit breaker (just replaced both of these). I don't see any others on the schematic.

Now I'm wondering about the compressor clutch. I was back there a few minutes ago noticed that the face of the pulley is covered with a fine black powder. Could that be the clutch material? I don't remember seeing it before. If so, then would the failing clutch cause this symptom? Thanks.
jor
dougrainer
Nomad
May 26, 2014
Normally, when a Compressor pulls too many amps or the clutch is shorted, it will blow a fuse, they rarely use a resettable circuit breaker. A resettable will not cycle (reset) that quick. You need to find the Hi pressure switch, usually located at the engine compressor area. There also may be a low pressure switch but based on your first post (40 and then 90 on compressor shut down) that is not a factor. If the 12 volt tstat is bypassed, then the Hi pressure switch is suspect as long as you have at least 100 to 140 psi on the hi side when running. If you do NOT have a hi gauge, and the system is 134a, install just 1 can and see if the compressor stays ON. 134a systems will ALWAYS have bubbles in the sight glass when fully charged. Freon 12 systems you will NOT have bubbles when fully charged. The compressor cycle time is just what you would see from a low charge and the hi pressure switch kicking in and out. Doug
MrWizard
Moderator
May 26, 2014
"thermal reset circuit breaker" is tripping (aka doing its job)

compressor clutch is bad..too much current

or the circuit breaker is bad

it looks like a large black fuse with two wires attached

will be located in chassis main wiring loom aka front firewall area ?
joraz
Explorer
May 26, 2014
OP here. Fired up the rig and turned on the A/C. Started cooling and then, of course, the compressor started cycling. I bypassed the T-stat (believe so anyhow) but the compressor continued to cycle. I looked in the sight glass and didn't see any bubbles when the compressor was on but it only stays on for 4 or 5 seconds so not completely sure. Anyhow, what does it mean if the compressor does not run continuously when the T-stat is bypassed. Here's a photo of what I did. You can see the T-stat spade connectors and my bypass wire. Thanks.
jor
dougrainer
Nomad
May 26, 2014
marcsbigfoot20b27 wrote:
dougrainer wrote:
If it gets to the hi 50's then the charge is not a factor. Low charge would cause short cycling at the beginning. I would suspect a BAD tstat. Jump the 2 wires on the Tstat (the tstat is at the Evaporator) and see if it stops cycling. Doug

There is no tstat per se, on a fixed orifice cycling clutch system. The pressure of the low side (which is directly related to temperature of the evap) is the "thermostat" if you will.

Reasons for low pressure shut off are:
Protect compressor due to really low charge......no freon , no oil.
Protect compressor from getting liquid in low side port.....no evap fan or iced evap.
Prevent evap from getting to cold in higher humidity and freezing evap and blocking airflow.

I have been working ON and fixing RV CLASS A Motorhome Dash AC systems for 35 years. NO RV CLASS A DASH AC system uses a Orifice type system. They ALL use a 12 volt point type Tstat that has the sensor INSTALLED the Evap fins. THAT tstat is what controls the power to the compressor as long as the pressure switches and coolant charge is correct. Doug
j-d
Explorer II
May 26, 2014
Looks like it's a TXV system what with that Receiver/Drier right next to the Condenser. Next Stop Evaporator Sensor sounds like a good plan.

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Cycling A/C Compressor

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