Dash Heat and Dash Air Conditioning Not Working

[dandick66]

2012 Diplomat.  The AC is not cooling and the heat is not heating.  I have done some troubleshooting and am at a loss.

All of the dash functions work - blower, AC buttons illuminate, mode selector works properly (floor, vent, defrost).  
I have bypassed the thermostat/thermistor at the evaporator box.  
The condenser fan is working and the AC high side line gong to the expansion valve is cold (45 degrees).  
The expansion valve is cold to the touch and measures 45 with a temp gun.  
The low side line going to the expansion valve is at ambient temperature.  
When I rotate the temperature control knob, there is no change in temperature.  The system just blows ambient air.  I tested the voltage going to the blend actuator and it is working properly.  
 

I am not well versed in AC, but I know the low side should be cold and the hight side should be warm or hot.  Why would this system be doing the opposite?  Also, I did tap the expansion valve with a screwdriver handle - no change.  
 

Bottom line is the AC is not cold and the heat is not hot.  
 

[Idoc57]

Dan,

Have you checked the heater control valve?  It sounds like you might be getting some coolant getting past the valve. That would cause your heater core to get warm, very warm or hot depending on how much hot water (coolant) might be passing through it.  That could kill the 45 degree cooling effect of your evaporator core, thereby giving you ambient temp air coming out of the dash registers.  Also, be sure to check the cable from the dash temperature control knob to the heater control valve.  Sounds like when you adjust your temp at the dash, your valve is not moving.

Carey

[Gary Cole]

2 hours ago, dandick66 said:

AC high side line gong to the expansion valve is cold (45 degrees).  

 

Dan that would suggest a compressor problem. No pressure, no heat.

[trailmug]

Could be a gross undercharge? Refrigerant liquid flashing off in the small liquid line before reaching the expansion valve. I think the receiver (black can that feeds the expansion valve) would be frosty in that case. These units don't have a low pressure / cycling switch, so it would probably be happy to run like that if there's enough pressure to close the high side binary switch (blue wires). Need to consult some gauges.

Edited August 23 by trailmug

[dandick66]

I have checked the heater control valve and it is working correctly.  
I went out to the coach this morning and connected the AC gauges.  I read somewhere that status pressure should be close to ambient - it is.  Then I started the coach and turned the AC on and it’s not working at all now.  The condenser fan is not turning.  All fuses are good.  If the static pressures were good, could it still be low on Freon?  
 

I’m thinking that I must have 2 problems.  The heater should work regardless if there’s an AC problem.  I am having a real problem trying to figure out what is going on.  It’s like the system is only allowing fresh air to flow through the ductwork no matter where the temp knob is.  There are 3 blend door/actuators on the plenum assembly.  I wonder if one or more of them are a problem.  I would think that they only control the flow of air to dash/feet/defroster.  I haven’t been able to find a system schematic or any description of how things are supposed to operate.  

[cbr046]

6 minutes ago, dandick66 said:

I went out to the coach this morning and connected the AC gauges.  I read somewhere that status pressure should be close to ambient - it is.  Then I started the coach and turned the AC on and it’s not working at all now.  The condenser fan is not turning.  All fuses are good.  If the static pressures were good, could it still be low on Freon? 

 

We can't read the AC gauge . . . too blurry.

Your AC gauge should have a temp reading on one of the scales, hopefully (and probably) matched for R134.  That "temp" should match ambient temp provided the engine hasn't been run, which would raise ambient temp in the engine bay and lines.  If it does match (or close) you can try shorting the freon low pressure switch on the low (suction) side up by where you connected the gauges.  Start the engine, turn AC on MAX and fan on HI.  This will tell you if you have low freon or a bad switch.  If the freon is low don't run it very long without charging up freon, and don't overcharge the system.

- bob

 

[dandick66]

Sorry about the blurry picture.  Don’t know why that happens.  Anyhow, the outside temperature this morning was about 75 and that is what the gauges read - both low and high.  
I do not see a switch on the low pressure side.  There is a switch on the high side, though.  I would think that it opens if the pressure is too high.  

[CAT Stephen]

@dandick66,

 

Here is the procedure to verify if your R134A refrigerant load is good:

1. Attached your manifold gage set to the schrader valves

2. Start your engine

3. Set your dash AC to maximum cool and set your dash airflow to the max position

4. Measure the current ambient air temperature outside

5. While the compressor is running, record both the high side and low side pressures after they stablize.

6. Use this P/T chart to verify if they are in range per your current ambient temperature: https://www.btrac.com/documents/r-134a-pressure-temperature-chart.pdf

[dandick66]

3 hours ago, CAT Stephen said:

@dandick66,

 

Here is the procedure to verify if your R134A refrigerant load is good:

1. Attached your manifold gage set to the schrader valves

2. Start your engine

3. Set your dash AC to maximum cool and set your dash airflow to the max position

4. Measure the current ambient air temperature outside

5. While the compressor is running, record both the high side and low side pressures after they stablize.

6. Use this P/T chart to verify if they are in range per your current ambient temperature: https://www.btrac.com/documents/r-134a-pressure-temperature-chart.pdf

Thanks.  I will get this checked out tomorrow.  Since the compressor is not engaging I will jumper the binary switch.  I hope that’s ok for a short test like this.  
The pressures on the chart you linked look high.  I’m just want to confirm- if it’s 82 F ambient, my low pressure should be 90.  The high side pressure across the chart is 350, but that’s at 172 F.  I’m not sure if I’m reading it right.

 

[dandick66]

I checked the static pressure this morning and it was approximately 75 on both low and high side.  Then I bypassed the binary switch and started the coach.  I put the AC on max cold and fan on high.  The AC was blowing ambient air.   The expansion valve got cold again.  I’m not sure if you can read these pressures in the attached picture, but they were really low.  The high side was about 40 PSI and the low side was actually below zero.  I didn’t realize that was possible.  Can I just add some R134 and watch the pressures?
 

[Ivan K]

That would inicate that you are very low on freon and the compressor is working. Unless you lost a lot of oil, that might be all it needs. Besides finding the leak point...to make it last.

[trailmug]

Most of these guys seem to take 4 lb. I bet you have less than a pound left. Since the low side is pulling into vacuum you might be well served to evacuate the system and recharge (in case your leak is on the low side and it's sucking in air when running).

I'd recommend first hooking up a R134a can and let it feed in gas (can right side up) with the system off. You can leave it like this without worrying about the quantity as it'll stop when the vapor pressure equalizes. Then you'll have enough pressure to soap bubble test. I don't personally find much use in UV dye.. barrier hoses don't tend to develop leaks (though the crimps sure do) and PAG oil leaves an oily spot if the leak is big enough to eject dye.

Edited August 25 by trailmug

[dandick66]

17 hours ago, Ivan K said:

That would inicate that you are very low on freon and the compressor is working. Unless you lost a lot of oil, that might be all it needs. Besides finding the leak point...to make it last.

 

7 hours ago, trailmug said:

Most of these guys seem to take 4 lb. I bet you have less than a pound left. Since the low side is pulling into vacuum you might be well served to evacuate the system and recharge (in case your leak is on the low side and it's sucking in air when running).

I'd recommend first hooking up a R134a can and let it feed in gas (can right side up) with the system off. You can leave it like this without worrying about the quantity as it'll stop when the vapor pressure equalizes. Then you'll have enough pressure to soap bubble test. I don't personally find much use in UV dye.. barrier hoses don't tend to develop leaks (though the crimps sure do) and PAG oil leaves an oily spot if the leak is big enough to eject dye.

I have a 30 lb canister with some Freon in it and I bought a couple of cans of R134 yesterday, hoping to get it working.  Well, the seal/gasket is missing on the yellow hose,  so I couldn’t use the 30lb canister.  I  ordered spare seals last night.  Then I decided to try the small can and apparently they’ve changed the design, so my older can fitting and hose won’t work on the new self sealing cans.  I will get a new can adapter fitting, too.  
 

I don’t have a vacuum pump, so I can’t evacuate the system.  I can pick one up or borrow one if necessary.  Is there any harm (other than the cost) to just charge it and see how long it lasts?  The weird thing is that when I was exercising the coach last week the AC was blowing out the vents at 38F.  The ambient was about 65, if I remember correctly.  

[CAT Stephen]

@dandick66

 

You do not need to evacuate the system because it is not empty.  If it was empty, then evacuating an AC system is a must to prevent contamination.  For now, you should proceed to just charge your system then see if it maintains pressure over a three day period.  

To charge your system:

1. Attach a can of R134a to your manifold gage set

2. Attached your manifold gage set to the schrader valves

3. Start your engine

4. Set your dash AC to maximum cool and set your dash airflow to the max position. 

5. Measure the current ambient air temperature outside

6. While the compressor is running, record both the high side and low side pressures after they stablize according to your current outdoor ambient temperature and verify if refrigerant charge is sufficient by using this chart: https://www.acprocold.com/help-and-advice/system-pressure-chart/. 

7A: Instructions for 30lb Cylinder: Using your 30 lb freon cylinder, open the freon inlet valve to allow your system to charge while continuing to monitor your high and low side pressures then close the freon inlet valve after you have attained pressures in range.  Only verify pressures when your compressor is running and the pressures have stabilized.

7B: Instructions for small cans: Attain ~2 gallons of hot water that is not painful to the touch (~130 F) and place the freon can in a bowl of the hot water tall enough to cover the freon can.  Using your small freon can, open the freon inlet valve to allow your system to charge while dipping the can fully in the hot water and occasionally opening and closing the freon inlet valve to give the heat time to boil the freon from liquid to gas.  NEVER invert the can as the result will be to inject liquid freon into your compressor which may result in compressor damage or destruction.  Continue to monitor your high and low side pressures then close the freon inlet valve after you have attained pressures in range.  Only verify pressures when your compressor is running and the pressures have stabilized.

Just so that you are aware, static pressures are not relevant and not useful for troubleshooting. 

[dandick66]

I made some progress, unfortunately my 30lb tank didn’t have much Freon in it.  I was able to get the low side to about 32 PSI and the high side about 125 PSI before it ran out.  The ambient here was 85 and very humid.  I had 56 degrees coming out of the vents.

 I have some appointments tomorrow, so I’ll have to resume this on Wednesday.  I will get more Freon and see if I can get the pressures up.  

[cbr046]

1 hour ago, dandick66 said:

 I have some appointments tomorrow, so I’ll have to resume this on Wednesday.  I will get more Freon and see if I can get the pressures up.  

Just don't get "Fake Freon" . . . . the labels can be quite misleading.

- bob

 

[dandick66]

On 8/26/2024 at 11:56 AM, CAT Stephen said:

@dandick66

 

You do not need to evacuate the system because it is not empty.  If it was empty, then evacuating an AC system is a must to prevent contamination.  For now, you should proceed to just charge your system then see if it maintains pressure over a three day period.  

To charge your system:

1. Attach a can of R134a to your manifold gage set

2. Attached your manifold gage set to the schrader valves

3. Start your engine

4. Set your dash AC to maximum cool and set your dash airflow to the max position. 

5. Measure the current ambient air temperature outside

6. While the compressor is running, record both the high side and low side pressures after they stablize according to your current outdoor ambient temperature and verify if refrigerant charge is sufficient by using this chart: https://www.acprocold.com/help-and-advice/system-pressure-chart/. 

7A: Instructions for 30lb Cylinder: Using your 30 lb freon cylinder, open the freon inlet valve to allow your system to charge while continuing to monitor your high and low side pressures then close the freon inlet valve after you have attained pressures in range.  Only verify pressures when your compressor is running and the pressures have stabilized.

7B: Instructions for small cans: Attain ~2 gallons of hot water that is not painful to the touch (~130 F) and place the freon can in a bowl of the hot water tall enough to cover the freon can.  Using your small freon can, open the freon inlet valve to allow your system to charge while dipping the can fully in the hot water and occasionally opening and closing the freon inlet valve to give the heat time to boil the freon from liquid to gas.  NEVER invert the can as the result will be to inject liquid freon into your compressor which may result in compressor damage or destruction.  Continue to monitor your high and low side pressures then close the freon inlet valve after you have attained pressures in range.  Only verify pressures when your compressor is running and the pressures have stabilized.

Just so that you are aware, static pressures are not relevant and not useful for troubleshooting. 

So, I went out this morning and added some more Freon.  The low side is about 33 PSI and the high side is changing from about 200-250.  It started out around 150 and after it ran for a while the pressure went up.  It is not moving fast between these pressures.  It creeps up to about 250, stays there for a while, then starts decreasing.  Sometimes it only drops about 10 PSI before it goes back up.  The ambient this morning is 82 and I have 53F coming out of the dash vents.  I certainly don’t want to overcharge the system.  

[CAT Stephen]

@dandick66,

 

You can ignore the lower pressure in the range on the high side because that is when your compressor cycles off and the pressure starts to drop from the stable peak pressure while the compressor is transitions from engaged to disengaged. 

The most probable cause of pressure under specification on the low side is that your refrigerant filter / dryer may be near end of life.  Here is a picture of an R134a Filter dryer for your reference:

- https://leisurervparts.com/acme-air-receiver-dryer-for-dash-air/

AC filter / Dryers often have a sight glass window that you can use to determine their condition.

Keep in mind that it is normal and customary for the low pressure side to peak below specification due to the exceptional length of refrigerant lines in coaches.  All R134a Pressure-Temperature charts are ideally suited for automotive dash AC systems and don't account for the effects of longer refrigerant lines associated with coaches.  What this means to you is that low side pressures are typically lower than spec when high side pressures are normal.  As an example on my 38' coach, I replaced my dash AC filter/dryer, venturi, and all schrader valves (six) and  my low side pressure is consistently ~10-12 PSI lower than the PT chart specification.  As you are ~17 PSI below spec given that your high side is definitely maximized, your filter / dryer should be replaced. 

Since you are experiencing an excellent temperature drop with your now fully charged dash AC, I recommend that you wait for ~3 days then measure your AC charge pressures again,  posting your results here in the forum.  Don't replace your AC filter / Dryer yet as there may be a leak issue that will be revealed in the coming days. 

[dandick66]

I was just getting ready to post today’s findings when your post came in.  
 

I Went out to the coach again this morning and everything is pretty much the same.  After running the AC for a few minutes, the low side creep up to about 250 and then dropped to about 200 and then started towards 250 again.  After about 10 minutes, the high side pretty much stabilized at 240.  Low side is about 33 still.  
 

I can see the dryer, but don’t know if it has the sight glass.  I will continue reading pressures for a couple more days.

Thank you for the help.

 

[trailmug]

Yes, this is great info. My 45' suction pressure ran about 15 PSI lower than expected, with full line flush, new condenser, new dryer, new TXV, new compressor. If you want to feel better about it, unplug the compressor while you're watching gauges and it'll shoot up quickly to the evaporator saturated pressure, which will be much higher and should be pretty close to recommended pressure.

The high side pressure will hunt for at least 10 minutes as the sensing bulb equalized to the system conditions. The aged TXV might continue hunting after that, but as long as you get good cooling, I wouldn't go looking for trouble 😁

I've got a "Dash A/C notes" text file in the files area with a bunch of random stuff in it. I wouldn't fret 17, but agree that a clogged receiver/dryer would behave similarly to a clogged expansion valve.. with significant clogging, you'd have a cold receiver and/or liquid line.

4 hours ago, CAT Stephen said:

@dandick66,

 

You can ignore the lower pressure in the range on the high side because that is when your compressor cycles off and the pressure starts to drop from the stable peak pressure while the compressor is transitions from engaged to disengaged. 

The most probable cause of pressure under specification on the low side is that your refrigerant filter / dryer may be near end of life.  Here is a picture of an R134a Filter dryer for your reference:

- https://leisurervparts.com/acme-air-receiver-dryer-for-dash-air/

AC filter / Dryers often have a sight glass window that you can use to determine their condition.

Keep in mind that it is normal and customary for the low pressure side to peak below specification due to the exceptional length of refrigerant lines in coaches.  All R134a Pressure-Temperature charts are ideally suited for automotive dash AC systems and don't account for the effects of longer refrigerant lines associated with coaches.  What this means to you is that low side pressures are typically lower than spec when high side pressures are normal.  As an example on my 38' coach, I replaced my dash AC filter/dryer, venturi, and all schrader valves (six) and  my low side pressure is consistently ~10-12 PSI lower than the PT chart specification.  As you are ~17 PSI below spec given that your high side is definitely maximized, your filter / dryer should be replaced. 

Since you are experiencing an excellent temperature drop with your now fully charged dash AC, I recommend that you wait for ~3 days then measure your AC charge pressures again,  posting your results here in the forum.  Don't replace your AC filter / Dryer yet as there may be a leak issue that will be revealed in the coming days. 

 

Edited August 29 by trailmug

[dandick66]

Here are my pressure results since Thursday.

I started the coach and ran the AC for 10 minutes at fast idle before I took the readings

Friday - Ambient 71F.  Dash vents 45F.  Low side 24 PSI.  High side 250 PSI.  I  disregarded the high side dropping periodically.  The high side did get to 260 for a very short time.  It is fairly steady at 250 PSI

Saturday - Ambient 73.  Dash vents 44.  Low side 24 PSI.  High side 250 PSI.  Like Friday, the gauge moved as high as 260 for a very short time.  
 

Sunday - Ambient 77. Dash vents 45.  Low side 24 PSI.  High side 250 PSI.  The high side gauge acted the same way it did on Friday and Saturday.  
 

As a side note, the heater is working now.  I rotated the control knob and the temperature increased.  I tried it several times each day, so I guess it fixed itself, or somehow it was related to the AC compressor not coming on.  
 

 

[dandick66]

On 9/1/2024 at 12:33 PM, dandick66 said:

Here are my pressure results since Thursday.

I started the coach and ran the AC for 10 minutes at fast idle before I took the readings

Friday - Ambient 71F.  Dash vents 45F.  Low side 24 PSI.  High side 250 PSI.  I  disregarded the high side dropping periodically.  The high side did get to 260 for a very short time.  It is fairly steady at 250 PSI

Saturday - Ambient 73.  Dash vents 44.  Low side 24 PSI.  High side 250 PSI.  Like Friday, the gauge moved as high as 260 for a very short time.  
 

Sunday - Ambient 77. Dash vents 45.  Low side 24 PSI.  High side 250 PSI.  The high side gauge acted the same way it did on Friday and Saturday.  
 

As a side note, the heater is working now.  I rotated the control knob and the temperature increased.  I tried it several times each day, so I guess it fixed itself, or somehow it was related to the AC compressor not coming on.  
 

 

@CAT Stephen, @trailmug

Here are more readings from Monday.

Ambient 77, dash vents 44, Low side 24 PSI, High side 255 PSI.  Looks like the pressures are holding and the temps are good.  Is the high side “too high”?  If so, how do I lower it?  

[CAT Stephen]

@dandick66,

 

The large differential between your high and low side is attributed to a  refrigerant filter / dryer may be near end of life.  In addition, you may also have a venturi that is partially obstructed by contamination.

As your cooling performance is currently excellent, I recommend that you defer:

- The replacement of the refrigerant filter / dryer

- The full AC system evacuation, flush, and refrigerant refill to remove any potential contamination from the venturi

Otherwise, enjoy your icy cold dash AC!

[dandick66]

2 hours ago, CAT Stephen said:

@dandick66,

 

The large differential between your high and low side is attributed to a  refrigerant filter / dryer may be near end of life.  In addition, you may also have a venturi that is partially obstructed by contamination.

As your cooling performance is currently excellent, I recommend that you defer:

- The replacement of the refrigerant filter / dryer

- The full AC system evacuation, flush, and refrigerant refill to remove any potential contamination from the venturi

Otherwise, enjoy your icy cold dash AC!

Thanks!  That sounds good to me.  I’ll probably research the dryer part number and get it so I have it on hand when the time comes.  Thanks again for the help.