Denso Dash A.C. Not Cycling 1996 Southwind Storm

[LaszloP]

Hello Fellow RVers,
I would appreciate your advice. I have replaced a lot of major system parts on my old RV (compressor, evap, hoses, thermostat, pressure switches, expansion valve) and the a.c. blows cold, but since it doesn't cycle on and off , it build pressure until it locks up. After the belt is replaced, all works again until the pressure builds up and the belt is prematurely warn down again.

I am assuming it is electrical but was wondering if I should focus on a specific area? Have you experienced this?

Thanks in advance

[allbrandauto]

I think you have a high pressure issue radiator fan condenser fan condenser fins need to be cleaned

[RLS7201]

You state a chevy chassis which should have an electric fan in front of the radiator that should run any time the A/C is on. That should be enough fan to keep the high side with in reason. There is an anti-icing switch in the evaporator case. You do have a high pressure switch and a low pressure switch, mounted close to the receiver dryer.
See downloads for complete wiring schematics of your Denso system.

Richard

[j-d]

If you've got 25psi Low Side, Evap Temp is around 27*F so after running awhile, it'll freeze. Once frozen, I think Low Side will drop even farther, and your new LPCO switch will stop the compressor.

If I'm looking at the right Temp/Pressure chart, 50psi will give you a 50*F evaporator. But even if you had 50psi low side, meaning much more refrigerant in the system, the high side shouldn't be above 300psi.

What's your ambient temperature? Any rear wheel drive vehicle is at a disadvantage compared to FWD. That's because FWD uses electric fans that provide full blow at idle/standstill. The RWD's, even with a massive fan and thermal clutch, have trouble cooling a R134A condenser at idle.

Something doesn't seem right. Fan Clutch failed, Radiator Shrouding missing, Condenser plugged with Bugs, Bug Screen in place (they really restrict air flow!), Engine Cooling System overheating... That, or it just can't get the air flow it needs without the coach moving. The old Class C would balk at idle, like stop lights, in Drive. I'd put it in Neutral to take pressure off the system.

Remember, you don't have a high pressure cutoff switch. The LPCO is on the low side. It doesn't care about high side pressure.

I'm gonna take a guess, that if you drive the coach and have a way to keep your gauge set hooked up, you'll see High come down, and also Low, probably to where your LPCO in fact shuts the compressor off.

[LaszloP]

Thank you. I replaced the cycle switch on the dryer but it didn't make a difference. It did not originally have a HP switch by the compressor but there is a port there. Just no wire or plug. The system was originally a 134a and I did the normal vacuum/oil fill/refrigerant fill per specs. I have run the system for a couple of hours today with no squeal or pressure over 300 sitting in my driveway LP in the 25 range. I just think that it should cycle like my accord... off and on. Is that what others have seen happen in their P30 systems?

Also, the cycle switch still has continuity even at the ~300 pressure range so not sure when that device will turn off...

[Chum_lee]

Clearly, you have had the system open. Did you replace the receiver/drier then purge and evacuate the system before recharging with the correct amount of the proper oil/refrigerant? If not, you very likely have contamination (air/water/metal fragments) in your system and most likely you are headed for disaster. Texas humidity!

Chum lee

[j-d]

LaszloP wrote:
There isn't a pressure switch on the compressor but there is a pressure switch on top of the drier. I didn't replace that one... wonder if that is the culprit?

Thank you for the prompt response.

GM P Series Chassis.

Odd, I usually have Too Much Coffee!

If you have the typical GM A/C system, it cycles only when the LOW side gets down into the low 20's of PSI. They're called Clutch Cycling Orifice Tube (CCOT) and the "Cycling" part's actually a little misleading, since it's NOT cycling to control cabin temperature like a system with a thermostat does. Temp is controlled with a Blend Door that mixes cold air from the A/C Evaporator Coil with hot air from the Heater Core.

A 1996 vehicle should be on a 1996 or possibly a 1995 chassis. Auto A/C was changed over from the R12 that was used when auto A/C started in the 1950's, to R134A that's supposedly more ozone-layer-safe.

Do you have any labeling telling if the original refrigerant in fact WAS R134A? I ask because of my personal experience with "retrofitted" auto A/C systems. They will not tolerate being overcharged. The high side goes crazy high and the compressor will balk. Chirping belts, slipping clutch, etc. etc. On a retrofitted RV we had, the charge had to be kept below specs to not balk the compressor. On a car I did, compressor would balk till I added an additional cooling fan on the condenser.

A proper retrofit should include addition of a high side cutoff switch, and as noted above, many compressors have a port for one. The GM HR6, DA6, HT6, have the ports, and come with a "slug" in the port for applications that don't call for the switch.

[MEXICOWANDERER]

"Wait... not enough coffee yet" 🙂

Thank you

Gave me a smile of the week.

[LaszloP]

There isn't a pressure switch on the compressor but there is a pressure switch on top of the drier. I didn't replace that one... wonder if that is the culprit?

Thank you for the prompt response.

GM P Series Chassis.

[DRTDEVL]

Wait... not enough coffee yet. The high pressure transducer switch is generally on the back side of the compressor assembly, or in the high pressure line shortly after the exit from the compressor. The low pressure switch is generally on or near the receiver/drier assembly.

[DRTDEVL]

Find the high pressure switch... it isn't triggering shutdown.

I would have to see your specific system to know where it is, but its usually on the Accumulator/Receiver/Dryer assembly. What chassis?