Coleman-Mach 48008-966 AC large voltage drop

[5215]

Back in October I got a new Coleman-Mach 48008-9660 3 P. S. heat pump and a 9630-715 non-ducted ceiling assembly.

With warmer weather, I've noticed a problem with the air conditioning. On LOW COOL or HIGH COOL, with the temperature knob in an intermediate position between coldest and warmest, after a few minutes of operation, the fan noise suddenly decreases markedly, and the voltage drops to roughly 106 volts. After 2-3 seconds, the fan noise and the voltage return to normal. However, when on the genset or at an RV park with marginal voltage, the voltage drops so low that my surge protector disconnects, turning off all AC electricity in the RV.

When first turned on, air conditioning starts normally, with only a slight voltage drop. There's never a problem if the temperature knob is at the coldest setting. There's never a problem on HIGH HEAT (heat pump). The RV has 30 amp service. There's no wall thermostat; all controls are in the ceiling assembly.

I could be totally wrong, but it seems like the compressor stops and then restarts after 2-3 seconds.

Does anyone else have this problem?

Airxcel just says take it to a service center, and I guess I will.

BTW, the heat pump works well, though I wish it had a LOW HEAT setting; the fan is noisy on high.

[dougrainer]

https://www.airxcel.com/rv/coleman-mach/service-support/document-library?docId=6407

Or this one? Doug

[dougrainer]

https://www.airxcel.com/DesktopModules/RvProduct/Pdf/r593.pdf

Is this your plenum assbly? Doug

[dougrainer]

To the OP, MAKE SURE THE COLD TEMP SENSOR IS INSTALLED IN THE CORRECT AREA OF THE RETURN AIR PLENUM. If it too close to the evap it will cause short cycling. Also, if the separation plenum gasket is NOT installed correctly or has air leaks(will be cold air flowing to where the temp sensor is), that will also cause short cycling. Doug

[dougrainer]

Skibane wrote:

valhalla360 wrote:

Skibane wrote:
...

This is likely your issue (might be compounded by marginal park voltage which will result in higher amperage draws and amps are what triggers the breakers to trip.).

Newer electronic thermostats have a delay built in, once the compressor shuts off, it won't allow it to start again for a few minutes. This allows the pressure to drop allowing the compressor to start more easily.

"Anti short-cycle" timers are also commonly sold for retrofitting A/C units that weren't originally equipped with this feature - Example here.

I doubt this would work on a RV Mechanical tstat controlled system. The link refers to a 1.5 amp MAX current thru. The RV AC mechanical control tstat will be susceptible to the current load that the compressor pulls(up to 18 amps short milliamp load). The link shows a system that would be on the smaller(16 to 22 gauge) wires of a wall thermostat(24 volt) like in a house. RV wall tstat have a upper control board that is where the time delay is. The time delay is not on the wall tstat. Doug

[Skibane]

valhalla360 wrote:

Skibane wrote:
...

This is likely your issue (might be compounded by marginal park voltage which will result in higher amperage draws and amps are what triggers the breakers to trip.).

Newer electronic thermostats have a delay built in, once the compressor shuts off, it won't allow it to start again for a few minutes. This allows the pressure to drop allowing the compressor to start more easily.

"Anti short-cycle" timers are also commonly sold for retrofitting A/C units that weren't originally equipped with this feature - Example here.

[dougrainer]

Remember, he stated NO PROBLEM on HP mode. And same problem on CG and Genset power. Doug

[valhalla360]

Skibane wrote:
It sounds like your compressor is trying to re-start too soon.

After they have shut off, most compressors need some time for the refrigerant pressure to subside on the high-pressure side of the evaporator coils.

If too much of this pressure remains when the compressor attempts to start again, it makes the compressor work much harder while starting - or may even prevent it from starting.

While it's attempting to start against too much pressure, the compressor draws an excessive amount of current. If it fails to start, it will continue drawing a lot of current for a few seconds, until the overload protector opens the circuit supplying power to it.

During those periods with it is drawing excessive current, the voltage being supplied to the RV tends to drop - which makes the lights dim and the fan slow down.

This is likely your issue (might be compounded by marginal park voltage which will result in higher amperage draws and amps are what triggers the breakers to trip.).

Newer electronic thermostats have a delay built in, once the compressor shuts off, it won't allow it to start again for a few minutes. This allows the pressure to drop allowing the compressor to start more easily.

The fan makes most of the noise but if you listen closely, you can often hear the compressor kick on in the background. The compressor is by far the bigger load.

[Lwiddis]

Hughes also makes a plug-in voltmeter that sells for twenty-five bucks or so.

[dougrainer]

Since you have mechanical controls, I would suspect a BAD tstat. The points are opening and closing too fast and causing compressor short cycling. The bad thing about mechanical tstat systems is there is no 3 minute time delay built in the system for stopping short cycling. The ONLY difference between HP and COOL is the system reverses the coolant. So, if functional on HP and, then the problem points to the tstat, not a capacitor or compressor. Doug

[CA_Traveler]

Where did you measure the 106V? Have you tried a 50A pedestal with an adapter? Could be inadequate wiring/connection.

[BB_TX]

wa8yxm wrote:
.....
A "Soft start" or "Hard Start" kit (Really the same product depends on who is talking) might help.

Not really. Work in different ways.

https://www.softstartrv.com/difference-between-hard-start-and-soft-start/

[wa8yxm]

What you are hearing is the compressor start... For some reason (Too far from the park's distribution panel?) the current draw is enough to suck down the voltage.

A "Soft start" or "Hard Start" kit (Really the same product depends on who is talking) might help.

[Skibane]

It sounds like your compressor is trying to re-start too soon.

After they have shut off, most compressors need some time for the refrigerant pressure to subside on the high-pressure side of the evaporator coils.

If too much of this pressure remains when the compressor attempts to start again, it makes the compressor work much harder while starting - or may even prevent it from starting.

While it's attempting to start against too much pressure, the compressor draws an excessive amount of current. If it fails to start, it will continue drawing a lot of current for a few seconds, until the overload protector opens the circuit supplying power to it.

During those periods with it is drawing excessive current, the voltage being supplied to the RV tends to drop - which makes the lights dim and the fan slow down.

One way to increase the amount of time between compressor shut-off and re-start is to add some "thermal mass" to the temperature sensor. The extra mass requires more time to change temperature - which slows down the speed at which the sensor responds. So, you get longer delays between compressor shut-down and re-start.

Why my old Coleman had this problem, I installed a big wad of tinfoil over the temperature sensor, held in place with zip-ties.

It sounds hinky, but it works. :B

[BB_TX]

Is that 106 volts to the air conditioner or the whole trailer? If you have one, put an amp clamp meter around the air conditioner hot wire and see what the current is doing during the voltage drop. If you don’t have one, you can buy one relatively inexpensively at Home Depot, Lowes, or even Harbor Freight. You don’t need a high dollar meter for that.