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Old 07-12-2015, 12:34 PM   #1
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Conflicting AC Information

We have a new to us 2007 Affinity (ISX600) that is in the shop for some AC repairs. The diagnosis was a leaking compressor HP hose, stuck front expansion valve and an improperly size dryer.

Country Coach indicated the proper charge is 6 lbs.

After replacing the suspect parts, evacuating the system and recharging we are seeing 70 degree air temperatures out of the vents when the ambient air temperature is about 90 - 95 degrees. This means that there is a drop of 20 - 25 degrees across the evaporator. Gauge pressures were running 30/280 which rose to 43/340 as the system heated up.

The repair technicians feel that there should be a greater drop across the evaporator, something like 40 degrees but don't understand why it isn't lower. I have seen others on the internet quote a 20 degree drop and a 40 degree drop as normal for DP motorhome.

So I am perplexed. Is the system operating normally for a 2007 Affinity or do I still have a problem?
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Old 07-12-2015, 02:02 PM   #2
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Originally Posted by rvmaybe View Post
We have a new to us 2007 Affinity (ISX600) that is in the shop for some AC repairs. The diagnosis was a leaking compressor HP hose, stuck front expansion valve and an improperly size dryer.

Country Coach indicated the proper charge is 6 lbs.

After replacing the suspect parts, evacuating the system and recharging we are seeing 70 degree air temperatures out of the vents when the ambient air temperature is about 90 - 95 degrees. This means that there is a drop of 20 - 25 degrees across the evaporator. Gauge pressures were running 30/280 which rose to 43/340 as the system heated up.

The repair technicians feel that there should be a greater drop across the evaporator, something like 40 degrees but don't understand why it isn't lower. I have seen others on the internet quote a 20 degree drop and a 40 degree drop as normal for DP motorhome.

So I am perplexed. Is the system operating normally for a 2007 Affinity or do I still have a problem?


I will try to keep this short but....

We have a 2007 Inspire and I felt the same as you. The dash A/C didn't seem to work very well at all. Then one cool day we were traveling and I had the vent on at the dash outlets. I noticed when I put my hand in front of the vent the air was slightly warm. Not hot, but warmer than the outside air temp. Didn't make sense

What I found out after much work was when the heater was turned off hot coolant continued to flow through the heater core. There is a pump (some CC's have two, one front one rear) on the outside of the firewall that turns off, but because of the connections of the heater coolant lines on the engine, coolant will continue to flow all the time. This will heat up the air after it is cooled by the A/C system warming the dash air quite a bit.

My fix.... I opened the generator slide, found the two heater coolant lines and installed a 3/4" ball valve in one of the lines. This will stop the coolant flow when the valve is closed and allow flow when the valve is open. Sometimes it's a pain to have to open or close the valve, but it's worth it! This made a huge difference in the performance of my dash air. I can now travel in 100+ degree heat and the dash air will easily keep us comfortable.

Hope this help,
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Old 07-13-2015, 07:19 AM   #3
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Thanks Barney. I checked the heater hoses and they felt like they were at ambient temperature. When I turned on the heat they got very hot pretty quickly so I don't think they are leaking. Were your hoses warm to the touch when they were leaking?
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Old 07-13-2015, 07:24 AM   #4
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20-30 degrees drop is considered normal on most A/C systems but...

To be 100% sure you need temps into the evaporator and out
Into the condenser and out
And humidity both indoors and outdoors

And a book of charts
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Old 07-13-2015, 04:37 PM   #5
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20-30 degrees difference between input and output air in an automotive system is not normal. The temperature differential is dependent on system function, relative humidity and fan speed. Better function higher differential. Lower humidity higher differential. Lower fan speed higher differential.

To check that get in your car and turn the system to max cool on a hot day. You may have 95 degree input air but the out put will be closer to 45 if fan speed low and 55 degrees if fan speed high. My Magna, when driving the other day in 97 degree ambient, was delivering 47 degree air at the dash with fan speed low. This with system set to A/C bringing in outside air.

20-30 degree differential is about right for a household system because of high air movement.
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Old 07-13-2015, 06:37 PM   #6
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Today at lunch it was 108* outside, but the AC temp out of my '97 Lexus was 38*. And that was at idle. While I have yet to put the thermometer in the outlets of the CC, I'm fairly sure that I've got greater than a 20* drop from ambient. Me thinks there is another issue...
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Old 07-13-2015, 07:23 PM   #7
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We are sitting at Pleasant Harbor RV resort in Peoria where the outside temperature is 106, and we have 72 inside running 3 roof ACs. The wife is starting to complain about being cold!
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Old 07-13-2015, 07:49 PM   #8
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OK--we have some "apples and oranges" going on here--first the residential A/Cs on the roof do not exchange outside air so the differential is based on "ambient" air inside the coach. My understanding is the evaporator coil can only impart about 20-25 degrees to the ambient air flow. If the inside of the coach starts out at 100, then you would expect to see 75-80 temps coming out of the vents. As the inside of the coach cools, the "ambient" inside air temp drops; accordingly, if the inside temp was now 75, I would expect 55 to 50 at the vent. However, since cold air sinks, the air being pulled from floor level is probably cooler than at dash or ceiling so the diff would be lower than 55.

Since the dash A/C is capable of pulling in outside air or cooling only inside air based on the selector position, you would expect to see a larger differential from the ambient outside air since you are cooling mostly inside air. However, even with the much smaller volume of air to be "conditioned" in the average car vs the average coach, I have seen what seems to be a larger diff than 20-25 degrees coming from some car vents??????? Guess inquiring minds still want to know??????
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Old 07-14-2015, 12:13 PM   #9
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Thanks Barney. I checked the heater hoses and they felt like they were at ambient temperature. When I turned on the heat they got very hot pretty quickly so I don't think they are leaking. Were your hoses warm to the touch when they were leaking?
Yes and no. It appears the amount of coolant flowing when the heater is turned off is small so it seemed to take a while for the warm coolant to reach the front of the coach. The next time you are on the road try pulling off at a rest stop and leave the engine running while you check. This is how I found the problem in my coach.

Good luck,
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Old 07-14-2015, 01:06 PM   #10
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Hey, tomorrow is Prime Day at Amazon, order one of these:

http://www.amazon.com/Taylor-Classic...at+thermometer

Then run your AC when the engine is cold and see what you are getting out of the vents vs. when the coolant warms up. That should help you to eliminate the heater core which is used to modify the air temp out of the evaporator.

These AC systems are just parts bin automotive units, and it seems like CC preferred the Ford suppliers for many components from what I've seen. No big mystery IMHO other than really long hoses from the rear to the front!

You should see something in the low 40* range I would think, re-circ or not.

I've got to move mine out of the garage tonight, so I'll let her run a bit and post up what temps I see. Note where I live... AC here is pretty important this time of year!

I'm pretty sure though, if you put the AC on MAX (which in a car or RV is the wrong setting generally if the inside temp is higher than outside) it will engage the coolant stack fan more frequently, which will have an effect on how well the condenser does its' job.
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