loren6210@yahoo.com Report post Posted March 5, 2019 Should the HAVC vacuum pump run continuiosly or is there something that stops it when a certain vac. is reached? My system went in to default (defrost) and my pump does not have power to it. I thought it was the pump and ordered a new one but the pump works fine. Share this post Link to post Share on other sites
wolfe10 Report post Posted March 5, 2019 loren6210@yahoo.com, Welcome to the FMCA Forum. Some vacuum pumps have built in switches to turn them on/off. Other applications use a remote pressure switch to control power to the vacuum pump. No, the vacuum pump should not run continuously. That could indicate a leak for example, a loose or cracked hose or vacuum diaphragm. It could also indicate a bad pressure switch. Share this post Link to post Share on other sites
moonwink Report post Posted March 6, 2019 My specialty is residential and commercial HVAC/R. What is the purpose of this vacuum pump talked about here? Is it used to provide vacuum for the dampers on the dash heating and air conditioning dampers on a diesel MH? Just curious. If that's its purpose, then there should be reservoir that once the pump took it down to 25 inches or so of mercury, would cycle off until it the vacuum rose to 15 inches. That should be plenty to make the dampers operate. If that's not the purpose, enlighten me please. Share this post Link to post Share on other sites
jleamont Report post Posted March 6, 2019 Moonwink, vacuum is for the blend doors behind the dash. They all operate off of vacuum. Defrost is the default when not enough or no vacuum is present. Most will have an electric pump and some sort of storage, usually a small plastic tank within close proximity to the pump. The pump will usually overcome small leaks, I have had pumps that run but do not create vacuum. Leaks do not usually occur on their own, often created by someone bumping a hose loose. The majority of the time it’s the pump. Share this post Link to post Share on other sites
