Accessing A/C Return Air Vent?

AFMagnum · Feb 22, 2018

I have a 2018 BC 4010RD and the bedroom A/C is (what I believe) short cycling. It’ll run normally for a bit, shut off, then kick right back on within 15 seconds. I’ve checked all the vents, reset the system, cleaned the filters, set the fan to “high” instead of “Auto” but I think it’s time to get into the air ducks to see if everything is routing correctly. Specifically, I want to check to see if the partition between the return air vent and the air exhaust may be leaking (or missing/fallen over, etc) as I have read could happen. From what I understand, this could cause cold air to go straight to the condenser causing the short cycle.

Here’s my question: anyone know how to actually do this? I tried pulling the vents inside and looking into the ducks but I have no clue what I’m looking at or what I’m looking for. Where’s the partiontion for the return air vent and the air exhaust? Should I be pulling the A/C unit off to access the air ducks that way? Anyone have pics by chance?

wdk450 · Feb 22, 2018

Here is an old thread that had a LOT on the AC airflow problems. There are also other threads, some of them listed at the bottom of the old thread page under "Similar Threads" : https://heartlandowners.org/showthread.php/1069-AC-air-flow-problem-SOLVED

AFMagnum · Feb 22, 2018

Thanks. I did a search for “short cycling” and came up with different threads.

SHerrick · Feb 22, 2018

AFMagnum said:
I have a 2018 BC 4010RD and the bedroom A/C is (what I believe) short cycling. It’ll run normally for a bit, shut off, then kick right back on within 15 seconds. I’ve checked all the vents, reset the system, cleaned the filters, set the fan to “high” instead of “Auto” but I think it’s time to get into the air ducks to see if everything is routing correctly. Specifically, I want to check to see if the partition between the return air vent and the air exhaust may be leaking (or missing/fallen over, etc) as I have read could happen. From what I understand, this could cause cold air to go straight to the condenser causing the short cycle.

Here’s my question: anyone know how to actually do this? I tried pulling the vents inside and looking into the ducks but I have no clue what I’m looking at or what I’m looking for. Where’s the partiontion for the return air vent and the air exhaust? Should I be pulling the A/C unit off to access the air ducks that way? Anyone have pics by chance?

If you have a ducted system (there is no through roof unit) and you have a wall-mounted thermostat, the divider is accessible through the rooftop unit. Remove the top cowling and look straight down through the fan. You will see a divider there. Before doing that, though, use a non contact pyrometer and check temperature at both the intake and return vents. You should have a difference of more than 15 degrees. If the unit runs and does not develop that much, there is something wrong with the charge. If it gets to that temperature, it MIGHT be in the thermostat. If you aren’t reaching temp or you swap out your thermostats and the problem persists, there is a problem with the freeze sensor probe imbedded in your cooling coil. It plugs into your logic board mounted in the AC unit on the roof. Thin white wire. Test the temp first thing, though.

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AFMagnum · Feb 22, 2018

SHerrick said:
If you have a ducted system (there is no through roof unit) and you have a wall-mounted thermostat, the divider is accessible through the rooftop unit. Remove the top cowling and look straight down through the fan. You will see a divider there. Before doing that, though, use a non contact pyrometer and check temperature at both the intake and return vents. You should have a difference of more than 15 degrees. If the unit runs and does not develop that much, there is something wrong with the charge. If it gets to that temperature, it MIGHT be in the thermostat. If you aren’t reaching temp or you swap out your thermostats and the problem persists, there is a problem with the freeze sensor probe imbedded in your cooling coil. It plugs into your logic board mounted in the AC unit on the roof. Thin white wire. Test the temp first thing, though.

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Great info, thank you! Yes, I have a ducted system so this is exactly the troubleshooting I was looking for. Between this and the link wdk450 posted, I have enough to keep me busy this weekend.

SHerrick · Feb 22, 2018

AFMagnum said:
Great info, thank you! Yes, I have a ducted system so this is exactly the troubleshooting I was looking for. Between this and the link wdk450 posted, I have enough to keep me busy this weekend.

Contact me if you get stuck.

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NWILSON · Feb 23, 2018

We have 3 ACs in our Cyclone and all of them will "short cycle" sometimes (not all at the same time). The ducts seem to be flowing well. I can't nail down a reason or duplicate the situation at will. It just does it when it does it regardless of whether one two are all three are on. I'm wondering if it has something to do with the thermostats rather than the AC units themselves.

carl.swoyer · Feb 27, 2018

AFMagnum said:
I have a 2018 BC 4010RD and the bedroom A/C is (what I believe) short cycling. It’ll run normally for a bit, shut off, then kick right back on within 15 seconds. I’ve checked all the vents, reset the system, cleaned the filters, set the fan to “high” instead of “Auto” but I think it’s time to get into the air ducks to see if everything is routing correctly. Specifically, I want to check to see if the partition between the return air vent and the air exhaust may be leaking (or missing/fallen over, etc) as I have read could happen. From what I understand, this could cause cold air to go straight to the condenser causing the short cycle.

Here’s my question: anyone know how to actually do this? I tried pulling the vents inside and looking into the ducks but I have no clue what I’m looking at or what I’m looking for. Where’s the partiontion for the return air vent and the air exhaust? Should I be pulling the A/C unit off to access the air ducks that way? Anyone have pics by chance?

Check you communications cord on the back of the thermostat for green corrosion
Then check out the other end up on the AC unit on the roof.
Dielectric grease should be present in the comm cord connection, if it's not put some in.

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wdk450 · Mar 9, 2018

I have had my Bighorn since 2009, and got into the intake and exhaust ductwork to do the recommended sealing and air diversion baffle. The last few years in the summer, I have had short cycling of the compressor, and even high current tripping of the branch circuit breaker, along with inadequate cooling. I was resigning myself to buying a new AC this summer. I did the intake duct sealing job with regular duct tape before, and thought it might now be leaking air some. I went over the old job with ductwork METAL tape. This made a BIG difference. Compressor short cycling (the AC blowing air, but the compressor cut off probably due to the freeze sensor activating) seems to be a thing of the past. I bought a new start/run capacitor through E-Bay and will get up on the roof and install that soon, then monitor the running current with my clamp on ammeter at the AC hot wire out of the breaker.

Accessing A/C Return Air Vent?

AFMagnum

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wdk450

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AFMagnum

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SHerrick

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AFMagnum

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SHerrick

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NWILSON

Kentucky Chapter Leaders - retired

carl.swoyer

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wdk450

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