Ok this has me quite shocked, I have a A/C Manifold Gauge set so I decided to check to see what was going on to cause compressor to cycle off every 3 seconds or so when rear unit is on.
First I found that when I am using just the front unit (rear set to off) The compressor stays engaged and has a Low Pressure of approx. 45 PSI and the Hi Side pressure of Approx. 325 PSI ( this is with a 90° ambient temp) and it blows Ice cold air on both recirculate and fresh air setting.
Now what is strange is when I turn on the rear unit the Hi Pressure side climbs to approx. 450 PSI and I believe the Low Side is at 40 PSI, When it gets to 450 Psi Hi Side the compressor disengages until The Hi Side pressure drops below 300 PSI then re-engages and climbs to approx. 450 PSI again and continues to cycle and I noticed the air is no longer Cold.
Once I turn off the rear unit the system cycles like it did with rear unit on for 20-30 seconds then goes back to operating like it normally does with just the front unit on.


Any Ideas as to why this is happening?
Is there possibly something wrong with the rear evaporator? I assume there is some sort of valve that when rear unit is activated ( Turned On) it splits the hi side line and runs 1/2 to fron evaporator and 1/2 to the rear evaporator and then when it is turned off it sends all the hi side to front evaporator.
I just started noticing this about 2-3 weeks ago I thought we possibly had a leak or had low refrigerant as the A/C was cycling so often like Ihave seen systems that are low react but according to the little I know about the A/C the low Side pressure seems to be in the approx. range for the ambient temp.


I am trying to figure out what could be going on so I can decide if I want to just use the front only or take it in and spend a good Chunk of $$ to get the system fixed.
I would rather have an Idea of what could be going on without having to throw away money to have it tested when I could use that money to get it repaired if I decide I need to as I am sure someone on here knows exactly what could be causing this situation.


Thanks again.

 

no cold air from front and rear or only rear?

 

hi, the first thing to check is for correct (aircon) cooling fan operation ,as the fan running is the only thing that brings the pressure down,if you put the set of manifold gauges on and watch what happens.
the system has a high pressure fail safe or switch which when pressure is to high will shut of the supply to the air compressor(the systems pump),to stop any damage to the system ,as soon as the pressure drops the compressor will start again ,when the switch allows.
Have seen some European cars where the cooling fan is a multi speed type fan with up to 3 different speeds contolled by a rheostat or similar ,ie rover 75 ,when one or more of the cooling fan speeds are missing this can play havoc with the ac system.
cheers richard

 

Yes I did notice I have multi Speed fans also, I did not pay attention to see that Both Fans were running at Hi Speed when the pressure built up to cause the pump to disengage. I will check that later today as it Is supposed to be in the 90's again.
@CHRYSLER TECH With the rear unit on at first it blows cool air both front and rear but once it gets to where the system starts Hi-Pressure cycling then both front and rear start blowing semi warm air.
I did not think to hook up my Temp probe and see what the exact temps coming out of the vents were in comparison with outside temps but Like I said to MEATH1978 I will also check the temp with my probe when I check to see that both fans are running on Hi Speed when A/C is on (Or at least both running HI when A/C is Hi Pressure cycling)


BTW thanks for the replies, For some reason I am not getting notification in my email when I get replies I will have to see why that is, SO sorry for not responding earlier.