manholt Report post Posted February 25, 2017 The dash heater won't blow hot air, only cold. 2006 Tiffin Phaethon 40 DP. Thoughts? Carl Share this post Link to post Share on other sites
hermanmullins Report post Posted February 25, 2017 Carl, Check the water level in the radiator. Sometime when it is low it may not be able to push the heat all the way to the front. Also the flapper valve may not be functioning properly. We are here in Deming and it is 36 degrees. Herman Share this post Link to post Share on other sites
manholt Report post Posted February 25, 2017 We are at 29 and feels like 25 ! Ugh! Where is the flapper valve on a CAT 350? Share this post Link to post Share on other sites
desertdeals69 Report post Posted February 25, 2017 We had that happen once and we had to run an 1500 watt electric heater on the inverter while driving in freezing weather. Share this post Link to post Share on other sites
manholt Report post Posted February 25, 2017 Why not furnace ? Share this post Link to post Share on other sites
wolfe10 Report post Posted February 25, 2017 Carl, With engine warmed up, I would access the heater core (open the nose). Feel the hoses that go into the heater core. Some manufacturers add a ball valve in the line from engine to dash heater core (actually a good idea in case of a hose or heater core failure). Could have been done by chassis maker or Tiffin. Could also be a heater control issue. If you get that far into it, you will need to know the brand of the HVAC control. Share this post Link to post Share on other sites
manholt Report post Posted February 25, 2017 Brett, you know CAT engines, I don't and Linda has not had the coach long enough...her first DP. She had 3 other Class A's over a 30 year period. Carl Share this post Link to post Share on other sites
wolfe10 Report post Posted February 25, 2017 Carl, Doubt the dash heater issue has anything to do with the engine. Whether Caterpillar or Cummins they just supply water to the lines to the dash heater core. Share this post Link to post Share on other sites
desertdeals69 Report post Posted February 25, 2017 2 hours ago, manholt said: Why not furnace ? Because the heat vents are a ways back in the coach and your up in the front driving and its cold. Share this post Link to post Share on other sites
manholt Report post Posted February 25, 2017 DD69...good point. Thankfully my Aqua Heat vents are front to back and heated tile helps! Had tile heat on yesterday for 3 hours...kept it comfortable for driving... Share this post Link to post Share on other sites
wayne77590 Report post Posted February 26, 2017 Isn't there a vacuum hose that opens and closes the heater/AC vent? Mine is under the hood and there are reports of the vacuum line can split at the control. Easy fix if it is configured that way. Share this post Link to post Share on other sites
hermanmullins Report post Posted February 26, 2017 I seem to remember that a diesel does not produce a vacuum. I'm I right or wrong? Herman Share this post Link to post Share on other sites
kaypsmith Report post Posted February 26, 2017 Herman, you are correct, diesel motor does not produce vacuum. Although I had a Ford dump truck with a 3206 Cat that used vacuum over hydraulic brakes. It was equipped with a vacuum pump instead of an air compressor. My bus uses an electrically activated water valve to control heat for the heating system, and there is no flapper on this system, and not all systems are alike. Share this post Link to post Share on other sites
wolfe10 Report post Posted February 26, 2017 All correct. The dash HVAC systems in diesels do NOT get vacuum from the engine (since there is none). They have a small 12 VDC electric pump up in the dash area. If the vacuum pump, plumbing or control fails, the air will come out the DEFROST. Defrost is the "default" position. Share this post Link to post Share on other sites
manholt Report post Posted February 26, 2017 That's probably why Linda is getting cold air from fan...it's in default mode ?! Have had no chance to look at it and it probably would do no good until we get to chandler and parts are more readily available, than on this mountain! I also hate to work with frozen fingers.. Share this post Link to post Share on other sites
wolfe10 Report post Posted February 26, 2017 Carl, Is the air just coming out the defrost vents, OR is it coming out the selected vents but cold only? Very different issues. Share this post Link to post Share on other sites
manholt Report post Posted February 26, 2017 Brett. Selected vents. Share this post Link to post Share on other sites
wildebill308 Report post Posted February 26, 2017 Have you checked to see if you are getting hot water to the front of the coach yet? It could be as simple as the shut off valve in the hose from the engine. When I drive with the furnace on it keeps the coach nice and warm. Definitely beats no heat. Bill Share this post Link to post Share on other sites
manholt Report post Posted February 26, 2017 Bill, not my coach. No I have not as we are in a holding area and will leave for a 30 min. drive to RV Park and Rally...currently warm outside! Share this post Link to post Share on other sites
wayne77590 Report post Posted February 27, 2017 I stand my ground. Doesn't matter if the vacuum is from an engine or a 12 volt pump. If there is a split in the line, crack where it attaches to the thing-a-ma-jig that controls the damper - no warm air. As Brett has posted in another thread, check the electrical wires going to the pump to make sure they are connected. Also check the fuse panel for that same pump. Share this post Link to post Share on other sites
wolfe10 Report post Posted February 27, 2017 But, a bad vacuum pump or cracked vacuum line means the air will only come out the defrost vents since that is the default position. Carl says it is coming out the selected vents. That means the vacuum system is operational. Again, the water valve could be electrically controlled (as it is on or coach), it could me mechanical (i.e. cable) or it could be vacuum operated. So, yes it is possible there is still a problem in a part of the vacuum system, but not the pump or main plumbing. Share this post Link to post Share on other sites
wildebill308 Report post Posted February 27, 2017 I agree, the first thing I would do is see if the hose coming from the engine is hot. Bill Share this post Link to post Share on other sites
manholt Report post Posted February 27, 2017 Linda verified that when she turns on fan for heat = cold air thru vents. She switched over to defrost, hoping to get some warm air there, no, frozen. She understands the system, but not quite sure on a DP. She is as I mentioned earlier, totally proficient on Class A, gassers. Linda is a member of the Forum, I just can't for some reason get her back on it. Sure would make this easier! Share this post Link to post Share on other sites
jleamont Report post Posted February 27, 2017 Carl, DP or Gas coach, the dash heat works the same way other than how it gets vacuum. Get your infrared thermometer and see if the heater hoses are warm, make sure both are, that will tell you water/coolant is circulating through the heater core and back to the engine. If both are warm/hot (obviously make sure the engine is up to operating temperature) she most likely has a blend door problem. If one is hot and the other is cold or both are cold there could be a blockage, the blockage could be either a clogged heater core or a valve somewhere shut off as Brett Mentioned. Look closely for valves up front or in my case they are on the engine where the heater hoses connect. Has she had heat before? You mentioned she hasn't had this coach long.. If it worked before look around the engine, I have bumped mine partially closed while servicing it just from reaching around in the engine bay. If memory serves me.....the heater hoses on a CAT C7 come out just behind the starter, which would be on the passenger side of the coach, maybe warmed up crawl under and see if they are hot first. You know the drill, make sure the coach is in a safe position blocked...... Share this post Link to post Share on other sites
f442485 Report post Posted February 27, 2017 Most late model vehicles use an unabridged motor assemble to control the hvac mode doors. There should be three motors, one for temp blend, one for the mode doors and one that controls the fresh air door. My past experience has been either the fresh air motor or the temp blend door motor has stopped working. If the motors are receiving a ground signal from the control head and the motor doesn't move. the motor is defective. If there is no ground at the motor, the control head may be defective. Ford, GM and Monaco use the same motor assemble. , made by Delphi (a subsidiary of GM). The hot water control valve is also controlled electrically. Just my two cents worth. Share this post Link to post Share on other sites
