AC system replaced but still not cooling efficiently

robby830

Member
Joined
Jun 20, 2020
Messages
30
Reaction score
1
Hi, new 6.0 PSD Excursion owner of just a few months and new to the forums. Having a some AC issues hoping you guys can help with.

AC didn’t feel cold at times when I bought it. The vacuum pump went out and when I replaced it, seemed to have helped for a bit, but summer heat hadn’t arrived yet to really test it. Then on a recent trip, AC started blowing warm air when at idle. I put gauges on it and low pressure was around 60 and high pressure over 400! I sprayed water on the condenser and the high pressure would drop around 225. Turned out to be the fan clutch. Replaced it with 7.3 version with adapter and thought AC issue was solved.

Now with summer heat it’s not feeling that cold. Measured temperature in the cab and it varies between 55-70. I evacuated the system and checked the orifice tube. It had some yellow rubbery debris in it. I replaced the orifice and accumulator first to see if it changed anything. Still getting the same cabin temp but reading at the gauges seem normal (60/225). I went ahead and replaced condenser, compressor, accumulator, orifice tube, front evaporator and expansion valve. I flushed the lines and the rear evaporator. There was some metal debris that came out. I vacuumed the system for a couple of hours and recharged it with 68 ounces of refrigerant.

I’m still getting same readings with the gauges. Also notice that cab temperature climbs between 60-70 when the rear AC is on. With just front AC on, it’s between 50-60. Shouldn’t it be around 40 though? Also, is it normal for the cab temp to rise when rear AC is on?

Outside temp is currently between 80-90 in South Florida

Thanks in advance!
Robby


Sent from my iPhone using Tapatalk
 

Gnathv

Member
Joined
Jan 1, 2018
Messages
34
Reaction score
0
AC

This is some good info from another forum. Weighing it in is very important and you’ve done that. R134 at 60 lbs pressure is 62 temperature. You need less pressure on low side. You weighed your charge so it should be right unless you have way more oil in system than needed. I would look at air flow across coils both condenser and evaporators. Leaking blend door can cause excessive heat load and raise pressures. I’d take a look at air flow through rear evap as you’ve replaced the front already.

1. The evaporator core(s) (you have two) are great collectors of debris. Air is moving through them with no filtration so over time they become clogged with decaying leaves, hair, dirt, you name it. This both restricts air flow and decreases the ability of the coil to absorb heat from the passing air. Clean them both. You will need to pick out the big stuff, then use a spray on coil cleaner to dissolve the muck and then flush them completely clean.

2. Your system has one compressor feeding two pathways. The front is an orifice tube system, the rear and expansion valve system. The rear system will self regulate, the front not so much. If you are really interested in getting this working, have the system evacuated and then change the dryer and orifice tube. There are a couple variable orifice tubes available. They work best when there is limited airflow over the condenser and low compressor speed - such as idling in Houston traffic.

3. Clean the cooling stack. Not just the condenser, which is the great bugcatcher up front, but also the transmission cooler, radiator, intercooler - all of them. If the radiator is full of cat hair and mud, the fan isn't pulling any air across the condenser. You really would only need to replace the condenser if the fins are all bent to hades or if its leaking. Its already a parallel flow high efficiency unit.

4. Check your heater bypass valve. Its supposed to close of the flow of coolant through the heater core when the a/c is in the max position. There are aftermarket valves that you can manually shut off coolant flow completely for the (normally) 11 months of the year we don't need the heater. Thank Al Gore for this winter....

5. Proper charge. It really needs to be weighed in. Those of us who've been around since the inception of MVAC often times cheat and use gauge pressure and feeling the low side tube for temperature. Actually, on HVAC systems using temperature and gauge pressure to calculate superheat and subcooling are the only way to charge the big units because Freon quantity varies with the size of the tubing runs, but on a fixed system like yours, the engineers have calculated the optimum charge and you are unlikely to replicate it by gauge pressure alone ESPECIALLY since you have and orifice tube and an expansion valve drawing on the compressor output.

Hope this helps.
 

webb06

Active member
Joined
Aug 14, 2012
Messages
3,888
Reaction score
9
Location
Seneca, MO
It’s been a few years back but I worked on an 05 excursion that the rear ac wasn’t cooling well. Replaced expansion valve and still no change. Come to find out there was another orfice tube under the truck at the rear, basically right above the tailpipe and right before the ac line goes into the cab. Pretty sure it was an orfice tube anyway. It was some kind of screen but it’s been awhile since then


Sent from my iPhone using Tapatalk
 

robby830

Member
Joined
Jun 20, 2020
Messages
30
Reaction score
1
This is some good info from another forum. Weighing it in is very important and you’ve done that. R134 at 60 lbs pressure is 62 temperature. You need less pressure on low side. You weighed your charge so it should be right unless you have way more oil in system than needed. I would look at air flow across coils both condenser and evaporators. Leaking blend door can cause excessive heat load and raise pressures. I’d take a look at air flow through rear evap as you’ve replaced the front already.

1. The evaporator core(s) (you have two) are great collectors of debris. Air is moving through them with no filtration so over time they become clogged with decaying leaves, hair, dirt, you name it. This both restricts air flow and decreases the ability of the coil to absorb heat from the passing air. Clean them both. You will need to pick out the big stuff, then use a spray on coil cleaner to dissolve the muck and then flush them completely clean.

2. Your system has one compressor feeding two pathways. The front is an orifice tube system, the rear and expansion valve system. The rear system will self regulate, the front not so much. If you are really interested in getting this working, have the system evacuated and then change the dryer and orifice tube. There are a couple variable orifice tubes available. They work best when there is limited airflow over the condenser and low compressor speed - such as idling in Houston traffic.

3. Clean the cooling stack. Not just the condenser, which is the great bugcatcher up front, but also the transmission cooler, radiator, intercooler - all of them. If the radiator is full of cat hair and mud, the fan isn't pulling any air across the condenser. You really would only need to replace the condenser if the fins are all bent to hades or if its leaking. Its already a parallel flow high efficiency unit.

4. Check your heater bypass valve. Its supposed to close of the flow of coolant through the heater core when the a/c is in the max position. There are aftermarket valves that you can manually shut off coolant flow completely for the (normally) 11 months of the year we don't need the heater. Thank Al Gore for this winter....

5. Proper charge. It really needs to be weighed in. Those of us who've been around since the inception of MVAC often times cheat and use gauge pressure and feeling the low side tube for temperature. Actually, on HVAC systems using temperature and gauge pressure to calculate superheat and subcooling are the only way to charge the big units because Freon quantity varies with the size of the tubing runs, but on a fixed system like yours, the engineers have calculated the optimum charge and you are unlikely to replicate it by gauge pressure alone ESPECIALLY since you have and orifice tube and an expansion valve drawing on the compressor output.

Hope this helps.


I did remove and clean the rear evaporator. Wasn’t much on it. Do you know how to test the blend door?


Sent from my iPhone using Tapatalk
 

Latest posts

Members online

No members online now.
Top