Automotive Air Conditioning Information Forum (Archives)

Allen13331 on Sat April 14, 2012 2:02 AM

Year: 1996
Make: Country Coach
Model: Motorhome
Engine Size: Big
Country of Origin: United States

This question may seem a little strange since I am a newbie at automotive AC. I just dumped $1200 into getting my AC repaired on my motor home. I was wondering if it is possible to mount sending units on the high pressure side and the low pressure side that would allow monitoring in the cab. After a while I would guess that a guy could tell from the pressures when his air needed to be serviced. What is wrong with my logic and why won't it work?

Thanks

mk378 on Sat April 14, 2012 4:02 PM

Dial gauges are sometimes permanently mounted on big stationary systems. In a mobile system it's just something else that could leak.

Cussboy on Sat April 14, 2012 8:35 PM

Quote
Originally posted by: Allen13331
After a while I would guess that a guy could tell from the pressures when his air needed to be serviced.

A functional AC system does not need to be serviced. You monitor its performance every time you use it by its cooling performance.

Have fun.

Allen13331 on Sat April 14, 2012 11:05 PM

Allen13331 on Sat April 14, 2012 11:14 PM

The same could be said for an automobile engine, you don't need an oil indicator as long as your motor run OK. All I am asking is it possible to mount a sending unit (not a hose and meter) that will fit the high pressure side and the low pressure side. I am a guy that likes to monitor what is going on in his truck. If I had been monitoring the low pressure pickup of my diesel motor I would have saved myself about $2000. Now I monitor the low pressure side of my diesel. I would like to do the same for my air conditioning, call me weird but I sure don't understand why you should NOT monitor it.

buickwagon on Tue April 17, 2012 7:39 AM

Quote
Originally posted by: Allen13331
call me weird but I sure don't understand why you should NOT monitor it.

-lurk mode off-

Because the average person can't properly interpret the pressure readings? Many people fail to understand that the pressure is not an indicator of how much refrigerant is in the system or that "normal" readings vary from day to day, depending on the temperature and humidity and engine RPM. I just flipped open a GM FSM to grab some sample specs and the maximum pressures vary from 23/190 at 20%RH and 70°F to 55/375 @60%RH and 100°F.

The pressure won't tell you how much oil is in the system either.

What Cussboy said can and should be taken quite literally: monitor the cooling performance. If the system is somewhat undercharged, the pressures will still be about the same as if it was properly charged, but there won't be enough mass of refrigerant available to cool the air at the system's peak potential. The specified maximum air temperature of the centre cooling vent on that same chart at those same points is 42°F and 78°F, respectively, meaning this particular system can drop the ambient air temperature 23 to 28°F (when the engine is at 2,000rpm, all doors and windows are closed, temperature set to minimum and fan set to high).

So even though the pressure might look OK on a gauge, the system could be undercharged. From a maintenance/prevention perspective, if the system is undercharged, there is less refrigerant available to carry the oil back to the compressor. To put it all together, monitoring your system's cooling performance could extend the compressor life, but monitoring the system's pressures will not reveal a problem until it's too late.

-lurk mode on-


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