Front rooftop hvac issues -2007 diplomat

[Bill R]

26 minutes ago, 96 EVO said:

That's what I would expect to see with the remote sensor mounted there, but the OP was having the opposite problem, with his AC shutting down early 🤔.

Yes, his vent was blowing on the sensor causing the issue.   It is a bad location for a temp sensor and can easily be relocated.  

[Joe Lee]

Hello All!

I have been using this topic to help me diagnose my A/C problem. Thanks to all for documenting this so well!

My issue is with my rear Dometic Penguin (2002). The unit is ‘short cycling’. I have been using the attached Troubleshooting Guide and discovered what I believe is a missing Remote Temperature Sensor. It is WHITE as shown in the Guide. When I traced the wire from the control board to the sensor, I discovered that the sensor was missing. See Picture. 

 

It would appear someone in the past removed this sensor on purpose. The 5 button thermostat control is located in the bedroom.  

Would anyone know if this sensor is required?  Seems like it!
Could this missing sensor cause the ‘short  cycling’ problem?

My front A/C unit has this sensor and it is working properly.  

Thanks for your thoughts!

[Coach J]

5 minutes ago, Joe Lee said:

Hello All!

I have been using this topic to help me diagnose my A/C problem. Thanks to all for documenting this so well!

My issue is with my rear Dometic Penguin (2002). The unit is ‘short cycling’. I have been using the attached Troubleshooting Guide and discovered what I believe is a missing Remote Temperature Sensor. It is WHITE as shown in the Guide. When I traced the wire from the control board to the sensor, I discovered that the sensor was missing. See Picture. 

 

It would appear someone in the past removed this sensor on purpose. The 5 button thermostat control is located in the bedroom.  

Would anyone know if this sensor is required?  Seems like it!
Could this missing sensor cause the ‘short  cycling’ problem?

My front A/C unit has this sensor and it is working properly.  

Thanks for your thoughts!

My issue was the remote sensor in my front AC and the tech removed it and mine has had in issues since. So I don’t know. Seems like my fox was opposite of what you are saying. Unplugging mine sent the control the the main thermostat and now it works. 

[Joe Lee]

Hi Coach J - wow. Hoped I had found a problem. It does sound like the opposite of what you had. Hoping I had found a simple fix.

My continued thanks for this group!

I will continue the hunt for the short cycle problem. 

[Joe Lee]

Hi!  I’m still struggling to figure out my Dometic penguin rear AC that is short cycling. Today I tested the capacitors. My run capacitor is a 20+10. (If I’m reading it correctly!). The 20 side is reading at 18.6 2,10 side is reading at 10.29.

Could someone help me determine if this capacitor is good with these readings?

And, could this capacitor have any impact on the short cycling?

Thanks everyone and happy Friday!

Edited September 15, 2023 by Joe Lee

[Ivan K]

I am used to see no more than 6% tolerance on run capacitors. Yours is just a bit more, not by much so it is questionable or unlikely but I would change it just in case it causes the internal temp switch to activate in the compressor. Either way, it should make it easier on the motor and they are not too expensive if you don't buy from Dometic.

[Gary Cole]

Joe what is the time period of the short cycle? Ivan do these units have a low pressure switch?

[Ivan K]

10 hours ago, Gary Cole said:

Joe what is the time period of the short cycle? Ivan do these units have a low pressure switch?

No Gary, they do not have low pressure switch, at least mine don't.

If they did, you would have an instant test port and maybe they don't want that.

Edited September 16, 2023 by Ivan K

[Joe Lee]

10 hours ago, Gary Cole said:

Joe what is the time period of the short cycle? Ivan do these units have a low pressure switch?

Hi Gary - the short cycle lasts for about one minute. I have tried the fan in auto, high and low to see if there was a difference. No change. The compressor constantly short cycles at about 1 min. 

The only time I found the short cycle to change was after I ran the heat pump for about 10 mins. After that heat pump cycle, the A/C did stay on for about 8 mins. Then, it was back to the 1 min short cycle. 
 

[Joe Lee]

Question for someone what knows freeze sensors. I measured the ohms for my rear freeze sensor and I got a reading of 22k. The local RV shop thought it should be 32k. Both my front and rear freeze sensors measured about 22k. So, I’m thinking these are good.   I’m needing an expert to weigh in. 
 

could this cause the short cycling issue?  If so, I’m just going to buy 2 new ones!

[Gary Cole]

Joe the regular period does suggest a thermal overload resetting  as Ivan suggested. You can bypass all control functions, control board, and thermostat  by jumpering the contactor. Make sure both fans are running. The condenser fan probably runs off the contactor. You can start the evaporator fan with the thermostat.  Leave the thermal overload in the contactor circuit. If the compressor stops check to see if the thermal overload opened. If it did then you have nothing to lose by bypassing the overload since you have a brick as is. The purpose of the thermal overload is to  protect the compressor if it starts before system pressure equalizes. Your control board has a timer function which prevents this from happening. I don't know a lot about these particular units so this is just a general suggestion.

[Ivan K]

1 hour ago, Joe Lee said:

Question for someone what knows freeze sensors. I measured the ohms for my rear freeze sensor and I got a reading of 22k. The local RV shop thought it should be 32k. Both my front and rear freeze sensors measured about 22k. So, I’m thinking these are good.   I’m needing an expert to weigh in. 
 

could this cause the short cycling issue?  If so, I’m just going to buy 2 new ones!

The sensor resistance will change with temperature so you both can be right until you can measure them side by side but I doubt yours are bad if you can confirm resistance change with temp.

[Joe Lee]

21 minutes ago, Gary Cole said:

Joe the regular period does suggest a thermal overload resetting  as Ivan suggested. You can bypass all control functions, control board, and thermostat  by jumpering the contactor. Make sure both fans are running. The condenser fan probably runs off the contactor. You can start the evaporator fan with the thermostat.  Leave the thermal overload in the contactor circuit. If the compressor stops check to see if the thermal overload opened. If it did then you have nothing to lose by bypassing the overload since you have a brick as is. The purpose of the thermal overload is to  protect the compressor if it starts before system pressure equalizes. Your control board has a timer function which prevents this from happening. I don't know a lot about these particular units so this is just a general suggestion.

Thanks for the idea!  I have attached what I believe is the Thermal Overload. If this is the correct part, I did test it for continuity and it did have continuity. So, could it still be bad?

[Gary Cole]

Could just be opening prematurely. That's why you need to check it under load and at operating temperature.

[Joe Lee]

1 hour ago, Gary Cole said:

Could just be opening prematurely. That's why you need to check it under load and at operating temperature.

Hey Gary!  Thanks for sharing your time with me. I did test the thermal overload with and without the compressor running. Both situations test positive for continuity. 
 

I also swapped out the thermal overload between my front and rear a/c’s. No change in my short cycle problem. 
 

I’m done fighting today. Thanks for all the support!

Joe

[Dr4Film]

If a remote temp sensor is missing, then the master control thermostat becomes the temp sensor for the AC.. As an example, in my previous 02 Windsor the main 5 button CCC was in the bedroom. The remote temp sensor for the front AC was located on the bottom of an OH cabinet above the passenger's seat. If that sensor were not plugged in then the front AC would use whatever the temperature was in the bedroom to control when the front AC would come on and turn off.

I had a short cycling problem with a front Penguin in the Windsor years ago. I tired a whole bunch of stuff to fix it and could never correct the short cycling. I finally gave up trying then the rear AC failed. So I purchased and installed two new Penguin II's with a new CCC-2 thermostat back in October 2018.

[Joe Lee]

Well Folks - I can’t believe the solution for my A/C short cycling. I removed the filter material I was using and the short cycling stopped. Kinda embarrassed to share my solution, but perhaps it’ll help somebody else one day.  This filter material was about 1 inch thick. I just order some that is only 1/4 inch thick.  Seems to have helped. My A/C unit is now cycling about 3 times an hour. The temperature has not cooled down to the temperature that I have set on the thermostat, but this may be normal. Bottom line: the compressor will stay on for about 20-25 mins, then cycle off for about 4 mins, the turn back on.  It’s not freezing up, so I can’t determine why it’s cycling. But I’m much better off!

[Tom Cherry]

Some unknowing individuals lead by the myths posted on the internet will mess with the filter media.  The correct way to see if the air conditioner is cooling properly is to run it with CLEAN filter material.  Now, mine has filter material in the overhead shroud.  NOT familiar with yours...so you can try this.  Get an accurate thermometer.  Amazon sell the probe type that work...like an HVAC Tech carries in his shirt pocket.

Supco ST02 Stainless Steel Pocket Dial Thermometer, 5" Stem, 1" Dial, 0 to 220 Degrees F

pThe one above is really TOO high for a good HVAC Tech....maybe 150 DegF tops.  You CAN buy the fancy digitals.  Use HVAC Tech Thermometer in Amazon.  If you have an antique lab thermometer...like some of us...that works.

You want to let the system run for about an hour.  Pull out the filter...so you get good air flow.  A restricted air flow will fake people out.  Measure the intake air at the unit or where the filter used to be.  Then find the closest outlet and measure there.  The spec varies as to who read it and where they read it and if they understood it...if you get my drift.  

TYPCIALLY, if you are in the 20 Def F or Subtract the cooled (outlet) temp from the Intake (inlet) air intake and get 20....good to go.  The accepted range is 18 - 22...but folks will argue that it has to be tighter....19 - 21.  BUT, the misconception is that is is measuring 24 DegF.  OMG, I have a super unit.  OMG....the air filter is blocking the intake air...and you WILL get a higher Delta T, but it is not properly dehumidifying....as in NOT cooling and you have inadequate cooling.  So many of the home made "Air Intake" filters actually restrict the air flow...  and then folks take the "HIGHER Delta T and say...IT MAY BE OLD...but its a COOLIN' better than new"

Please pardon my sarcasm as it is often hard to convince folks that the above is the correct way and that a high Delta T is a sign of problems and will also shorten the life of their units.

If you have a OUTSIDE temp sensor like many do, then use that.  The accuracy is in the Delta T...so if the unit is not calibrated to a US Government standard...as long as it is close and consistent....then you focus on the Delta T.

That's it...you did make a great discovery.....and I would hope that some Windsor owners will chime in and provide a picture of what the original units had for a filter and such.  The 2009 units that I have don't have the fancy "TRAY" ceiling trim...just a white shroud and a charcoal black filter.  You can look on Amazon....the filter is really very porous...and you have to, in the hot summer with a lot of dust and in and out traffic, have to clean them every few weeks.  When we are on the road, I often clean them at least  monthly. Put the above in Amazon.  It is really OPEN CELL foam...for good air flow.  It is NOT a HEPA filter...so dust builds up.  Wash in soapy water and then rinse.  Roll up in a towel and twist...get the water out.  Then a little cool air from a hair dryer will get out the moisture.  Takes maybe 10 minutes.  

The above was what the techs said in the Lazy Days "How to get the MOST from your RV HVAC" seminars that I attended....

Replacement Return Foam Filter Compatible with Dometic Part # D3108015.003 - 15-7/8 x 12 x 1/4

[Gary Cole]

Glad you found the problem Joe. I'm going to pay more attention to my air filters. I replaced mine with  slightly more restrictive filters. I did increase the filter square in. Think I'll check my compressor run time just to make sure they didn't have an impact. You can buy a really nice toy with the money you didn't waste on new.  🙂

[Tom Cherry]

11 hours ago, Gary Cole said:

Glad you found the problem Joe. I'm going to pay more attention to my air filters. I replaced mine with  slightly more restrictive filters. I did increase the filter square in. Think I'll check my compressor run time just to make sure they didn't have an impact. You can buy a really nice toy with the money you didn't waste on new.  🙂

Checking Delta T is how HVAC techs evaluate performance.  This method is the gold standard for RV, homes, autos, etc. Do it with and without the filters in place.  As long as you are in the 18 - 22 DegF range or see no real difference in WITH & WITHOUT… then all is working well…

[Frank McElroy]

On 9/17/2023 at 4:21 PM, Joe Lee said:

Well Folks - I can’t believe the solution for my A/C short cycling. I removed the filter material I was using and the short cycling stopped. Kinda embarrassed to share my solution, but perhaps it’ll help somebody else one day.  This filter material was about 1 inch thick. I just order some that is only 1/4 inch thick.  Seems to have helped. My A/C unit is now cycling about 3 times an hour. The temperature has not cooled down to the temperature that I have set on the thermostat, but this may be normal. Bottom line: the compressor will stay on for about 20-25 mins, then cycle off for about 4 mins, the turn back on.  It’s not freezing up, so I can’t determine why it’s cycling. But I’m much better off!

Thanks for the update and sharing the solution.  I'm sure this will help others.  Air flow volume is critical and your post highlighted that important fact.

[Joe Lee]

My thanks to everyone for sharing their time and expertise. Well, within a day, my Dometic Penguin started short cycling again. The compressor will only stay on in ‘Cool’ mode for about 50 seconds. 
 

However, the ‘heat pump’ mode works very well. 
 

I’m going to retest all the components and use the advice already given. 

Here’s a few details on running the unit in Heat Pump mode:

I ran my Penguin for over 60 mins and, using my Pocket Thermometer (thanks Tom!), I’m showing a temperature Delta T of 35 degrees F. Intake temp = 92. Return temp = 127. Man - it’s hot in my bedroom!  The compressor remained on for the entire test for over 60 mins.   The unit didn’t Short Cycle a single time.  

Does the Heat Pump working well suggest anything else I should test/replace?  And, don’t all the components work the same way, just reversed to create heat or cold?  
 

Is there a way to test to Control Board?

Thanks for all the help!

[Tom Cherry]

2 hours ago, Joe Lee said:

My thanks to everyone for sharing their time and expertise. Well, within a day, my Dometic Penguin started short cycling again. The compressor will only stay on in ‘Cool’ mode for about 50 seconds. 
 

However, the ‘heat pump’ mode works very well. 
 

I’m going to retest all the components and use the advice already given. 

Here’s a few details on running the unit in Heat Pump mode:

I ran my Penguin for over 60 mins and, using my Pocket Thermometer (thanks Tom!), I’m showing a temperature Delta T of 35 degrees F. Intake temp = 92. Return temp = 127. Man - it’s hot in my bedroom!  The compressor remained on for the entire test for over 60 mins.   The unit didn’t Short Cycle a single time.  

Does the Heat Pump working well suggest anything else I should test/replace?  And, don’t all the components work the same way, just reversed to create heat or cold?  
 

Is there a way to test to Control Board?

Thanks for all the help!

You are now in the “Lippert, help me mode”.  A Delta 5 of 35 means….serious issues.  

First…..did you take out the improper or wrong filter.  A clogged filter or one that some unknowing individual put in without a clue will give you a high Delta T.   Take that to the bank.

Second….have you pulled the cover off and inspected the unit.  Look for torn gaskets or any sign that the air flow is being inhibited?  Pull the other unit.  Look at where the foam and such are located.

Third….how dirty or crappy is the condenser coils.  Amazon or HVAC distributors sell coil cleaning products.  Ever cleaned them?

Fourth….start googling..  get the installation manual.  There is a complete troubleshooting guide in the back or near the end.

Fifth….get all your “data” and “tried this and whatever” and then call Lippert….

[Joe Lee]

Thanks Tom!  Here’s where I’m at:

1) I did replace the filter with a new appropriate filter material. 
2) I have inspected both units.  I didn’t see anything that looked out of place and both units looks alike. 
3) My first step was to clean both units with a coil cleaner recommended for RV A/C units.  No change and they didn’t see too dirty. My Rig spent the first 18 years of its life inside. 
4) I have the install manual and I believe I have completed those steps. 
5) Your next idea is to call Lippert. I did call Dometic. Would Lipper be a better source?  As I’m not a pro so, Dometic wasn’t very helpful.  
 

Today, I replaced the PTCR (Postive coefficient thermal resistor). My short cycle times changed from the compressor being on for 50 seconds to about 5 mins.  Progress but must not be the solution. 
 

Thanks for the heads-up on the front unit being in trouble as well since the Delta T is too great.  Seems it may be time to give up on the repairs unless a call to Lippert or a professional will help. What do y’all think?

Thinking of adding a Remote Thermostat to the Rear Unit that is short cycling.  This would eliminate the thermostat at the main thermostat unit on the wall.  Also, thinking of replacing the thermostat and control board next.  Thoughts if this is a waste of time and money?

At least isn’t getting cooler in Amarillo TX! Hoping to be out of here in the next month. 

[Guest Ray Davis]

8 minutes ago, Joe Lee said:

Today, I replaced the PTCR (Postive coefficient thermal resistor). My short cycle times changed from the compressor being on for 50 seconds to about 5 mins

That's interesting,  I don't know but it seems to point toward the compressor.

There is a 40 plus yr tech in the Dallas area and he hangs out on this forum & goes by dougrainer  Doug has seen lots of things    https://forums.goodsamclub.com/index.cfm/fuseaction/thread/tid/30409153.cfm